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| author | Eduardo Chappa <chappa@washington.edu> | 2013-11-02 02:51:18 -0600 |
|---|---|---|
| committer | Eduardo Chappa <chappa@washington.edu> | 2013-11-02 02:51:18 -0600 |
| commit | 7fe712882b909931088a318c08041b0e7974a000 (patch) | |
| tree | 2770f9b084e2efc7fc55e96e9bf4352cf2ff33a3 /imap/docs/rfc | |
| parent | bdfc834badee92ceeb2befe02f1d065ced5b9ddf (diff) | |
| download | alpine-7fe712882b909931088a318c08041b0e7974a000.tar.xz | |
* Update to version 2.19.1
* Upgrade UW-IMAP to Panda IMAP from https://github.com/jonabbey/panda-imap.
* Replace tabs by spaces in From and Subject fields to control for size in
screen of these fields. Change only in index screen display.
Diffstat (limited to 'imap/docs/rfc')
59 files changed, 49932 insertions, 0 deletions
diff --git a/imap/docs/rfc/README b/imap/docs/rfc/README new file mode 100644 index 00000000..b808150e --- /dev/null +++ b/imap/docs/rfc/README @@ -0,0 +1,87 @@ +The following documents are necessary to understand the syntax rules +most of the remaining documents. Note that some documents refer to +RFC 2234 which has been replaced by RFC 5234: + rfc5234.txt Augmented BNF for Syntax Specifications - ABNF + rfc4466.txt Collected Extensions to IMAP4 ABNF + + +The following documents specify the IMAP protocol: + rfc3501.txt Internet Message Access Protocol - Version 4rev1 + + +The following documents provide additional information which is useful +in understanding the IMAP protocol: + rfc1733.txt Distributed Electronic Mail Models in IMAP4 + rfc2180.txt IMAP4 Multi-Accessed Mailbox Practice + rfc2683.txt IMAP4 Implementation Recommendations + rfc4549.txt Synchronization Operations for Disconnected IMAP4 Clients + rfc5530.txt IMAP Response Codes + rfc5788.txt IMAP4 Keyword Registry + +The following documents describe extensions to the IMAP protocol. +Items marked with "*" are supported in this distribution: + rfc4314.txt ACL + rfc5257.txt ANNOTATE-EXPERIMENT-1 + * rfc3516.txt BINARY + rfc4469.txt CATENATE + * rfc3348.txt CHILDREN + rfc4978.txt COMPRESS + rfc4551.txt CONDSTORE + rfc5259.txt CONVERT + rfc5267.txt CONTEXT + rfc5161.txt ENABLE + * rfc4731.txt ESEARCH + rfc5267.txt ESORT + rfc5466.txt FILTERS + * rfc5255.txt I18NLEVEL=1 + rfc2971.txt ID + * rfc2177.txt IDLE + rfc5255.txt LANGUAGE + rfc5258.txt LIST-EXTENDED + rfc5819.txt LIST-STATUS + * rfc2088.txt LITERAL+ + * rfc2221.txt LOGIN-REFERRALS + * rfc2193.txt MAILBOX-REFERRALS + rfc5464.txt METADATA + * rfc3502.txt MULTIAPPEND + * rfc2342.txt NAMESPACE + rfc5465.txt NOTIFY + rfc5162.txt QRESYNC + rfc2087.txt QUOTA + * rfc4959.txt SASL-IR + * rfc5256.txt SORT + * rfc5256.txt THREAD + * rfc4315.txt UIDPLUS + * rfc3691.txt UNSELECT + rfc4467.txt URLAUTH + rfc5524.txt URLAUTH=BINARY + rfc5738.txt UTF8 (EXPERIMENTAL) + * rfc5032.txt WITHIN + + +The following documents describe SASL: + rfc4422.txt Simple Authentication and Security Layer (SASL) +and the SASL mechanisms supported in this distribution: + rfc4505.txt ANONYMOUS + rfc2195.txt CRAM-MD5 + rfc4752.txt GSSAPI + rfc4616.txt PLAIN + + +The following documents relate to internationalization issues: + rfc4790.txt Internet Application Protocol Collation Registry + rfc5051.txt i;unicode-casemap - Simple Unicode Collation Algorithm + rfc5738.txt IMAP Support for UTF-8 (EXPERIMENTAL) + +The following documents are primarily of historic interest: + rfc1732.txt IMAP4 Compatibility with IMAP2 and IMAP2bis + rfc2061.txt IMAP4 Compatibility with IMAP2bis + rfc2062.txt Internet Message Access Protocol - Obsolete Syntax + + +The following documents discuss matters which are related to IMAP: + rfc3503.txt MDN Profile for IMAP + rfc3656.txt MUPDATE Distributed Mailbox Database Protocol + rfc4468.txt Message Submission BURL Extension + rfc5092.txt IMAP URL Scheme + rfc5593.txt IMAP URL Access Identifier Extension diff --git a/imap/docs/rfc/rfc1732.txt b/imap/docs/rfc/rfc1732.txt new file mode 100644 index 00000000..cfae89c0 --- /dev/null +++ b/imap/docs/rfc/rfc1732.txt @@ -0,0 +1,283 @@ + + + + + + +Network Working Group M. Crispin +Request for Comments: 1732 University of Washington +Category: Informational December 1994 + + + IMAP4 COMPATIBILITY WITH IMAP2 AND IMAP2BIS + + +Status of this Memo + + This memo provides information for the Internet community. This memo + does not specify an Internet standard of any kind. Distribution of + this memo is unlimited. + +Introduction + + This is a summary of hints and recommendations to enable an IMAP4 + implementation to interoperate with implementations that conform to + earlier specifications. None of these hints and recommendations are + required by the IMAP4 specification; implementors must decide for + themselves whether they want their implementation to fail if it + encounters old software. + + IMAP4 has been designed to be upwards compatible with earlier + specifications. For the most part, IMAP4 facilities that were not in + earlier specifications should be invisible to clients unless the + client asks for the facility. + + In some cases, older servers may support some of the capabilities + listed as being "new in IMAP4" as experimental extensions to the + IMAP2 protocol described in RFC 1176. + + This information may not be complete; it reflects current knowledge + of server and client implementations as well as "folklore" acquired + in the evolution of the protocol. + + + + + + + + + + + + + + + + +Crispin [Page 1] + +RFC 1732 IMAP4 - Compatibility December 1994 + + +IMAP4 client interoperability with old servers + + In general, a client should be able to discover whether an IMAP2 + server supports a facility by trial-and-error; if an attempt to use a + facility generates a BAD response, the client can assume that the + server does not support the facility. + + A quick way to check whether a server implementation supports the + IMAP4 specification is to try the CAPABILITY command. An OK response + that includes the IMAP4 capability value indicates a server that + supports IMAP4; a BAD response or one without the IMAP4 capability + value indicates an older server. + + The following is a list of facilities that are only in IMAP4, and + suggestions for how new clients might interoperate with old servers: + + CAPABILITY command + A BAD response to this command indicates that the server + implements IMAP2 (or IMAP2bis) and not IMAP4. + + AUTHENTICATE command. + Use the LOGIN command. + + LSUB and LIST commands + Try the RFC 1176 FIND command. + + * in a sequence + Use the number of messages in the mailbox from the EXISTS + unsolicited response. + + SEARCH extensions (character set, additional criteria) + Reformulate the search request using only the searching + options listed in search_old in the IMAP4 grammar. This may + entail doing multiple searches to achieve the desired + results. + + BODYSTRUCTURE fetch data item + Try to fetch the non-extensible BODY data item. + + body section number 0 + Fetch the entire message and extract the header. + + RFC822.HEADER.LINES and RFC822.HEADER.LINES.NOT fetch data items + Use RFC822.HEADER and remove the unwanted information. + + BODY.PEEK[section], RFC822.PEEK, and RFC822.TEXT.PEEK fetch data + items Use the corresponding non-PEEK versions and manually + clear the \Seen flag as necessary. + + + +Crispin [Page 2] + +RFC 1732 IMAP4 - Compatibility December 1994 + + + UID fetch data item and the UID commands + No equivalent capabilitity exists in older servers. + + FLAGS.SILENT, +FLAGS.SILENT, and -FLAGS.SILENT store data items + Use the corresponding non-SILENT versions and ignore the + untagged FETCH responses which com eback. + + + The following IMAP4 facilities were introduced in the experimental + IMAP2bis revisions to RFC-1176, and may be present in a server that + does not support the CAPABILITY command: + + CREATE, DELETE, and RENAME commands + To test whether these commands are present, try a CREATE + INBOX command. If the response is NO, these commands are + supported by the server. If the response is BAD, they are + not. Older servers without the CREATE capability may sup- + port implicit creation of a mailbox by a COPY command with a + non-existant name as the destination. + + APPEND command + To test whether this command is present, try to append a + zero-length stream to a mailbox name that is known not to + exist (or at least, highly unlikely to exist) on the remote + system. + + SUBSCRIBE and UNSUBSCRIBE commands + Try the form of these commands with the optional MAILBOX + keyword. + + EXAMINE command + Use the SELECT command instead. + + flags and internal date argument to APPEND command + Try the APPEND without any flag list and internal date argu- + ments. + + BODY, BODY[section], and FULL fetch data items + Use RFC822.TEXT and ALL instead. Server does not support + MIME. + + PARTIAL command + Use the appropriate FETCH command and ignore the unwanted + data. + + + IMAP4 client implementations must accept all responses and data for- + mats documented in the IMAP4 specification, including those labeled + + + +Crispin [Page 3] + +RFC 1732 IMAP4 - Compatibility December 1994 + + + as obsolete. This includes the COPY and STORE unsolicited responses + and the old format of dates and times. In particular, client imple- + mentations must not treat a date/time as a fixed format string; nor + may they assume that the time begins at a particular octet. + + IMAP4 client implementations must not depend upon the presence of any + server extensions that are not in the base IMAP4 specification. + + The experimental IMAP2bis version specified that the TRYCREATE spe- + cial information token is sent as a separate unsolicited OK response + instead of inside the NO response. + + The FIND BBOARDS, FIND ALL.BBOARDS, and BBOARD commands of RFC 1176 + are removed from IMAP4. There is no equivalent to the bboard com- + mands, which provided a separate namespace with implicit restrictions + on what may be done in that namespace. + + Older server implementations may automatically create the destination + mailbox on COPY if that mailbox does not already exist. This was how + a new mailbox was created in older specifications. If the server + does not support the CREATE command (see above for how to test for + this), it will probably create a mailbox on COPY. + + Older server implementations may not preserve flags or internal dates + on COPY. Some server implementations may not permit the preservation + of certain flags on COPY or their setting with APPEND as site policy. + + + + + + + + + + + + + + + + + + + + + + + + + +Crispin [Page 4] + +RFC 1732 IMAP4 - Compatibility December 1994 + + +IMAP4 server interoperability with old clients + + In general, there should be no interoperation problem between a + server conforming to the IMAP4 specification and a well-written + client that conforms to an earlier specification. Known problems are + noted below: + + Poor wording in the description of the CHECK command in earlier + specifications implied that a CHECK command is the way to get the + current number of messages in the mailbox. This is incorrect. A + CHECK command does not necessarily result in an EXISTS response. + Clients must remember the most recent EXISTS value sent from the + server, and should not generate unnecessary CHECK commands. + + An incompatibility exists with COPY in IMAP4. COPY in IMAP4 + servers does not automatically create the destination mailbox if + that mailbox does not already exist. This may cause problems with + old clients that expect automatic mailbox creation in COPY. + + The PREAUTH unsolicited response is new in IMAP4. It is highly + unlikely that an old client would ever see this response. + + The format of dates and times has changed due to the impending end + of the century. Clients that fail to accept a four-digit year or + a signed four-digit timezone value will not work properly with + IMAP4. + + An incompatibility exists with the use of "\" in quoted strings. + This is best avoided by using literals instead of quoted strings + if "\" or <"> is embedded in the string. + +Security Considerations + + Security issues are not discussed in this memo. + +Author's Address: + + Mark R. Crispin + Networks and Distributed Computing, JE-30 + University of Washington + Seattle, WA 98195 + + Phone: (206) 543-5762 + + EMail: MRC@CAC.Washington.EDU + + + + + + +Crispin [Page 5] + diff --git a/imap/docs/rfc/rfc1733.txt b/imap/docs/rfc/rfc1733.txt new file mode 100644 index 00000000..2ec385f0 --- /dev/null +++ b/imap/docs/rfc/rfc1733.txt @@ -0,0 +1,171 @@ + + + + + + +Network Working Group M. Crispin +Request for Comments: 1733 University of Washington +Category: Informational December 1994 + + + DISTRIBUTED ELECTRONIC MAIL MODELS IN IMAP4 + + +Status of this Memo + + This memo provides information for the Internet community. This memo + does not specify an Internet standard of any kind. Distribution of + this memo is unlimited. + + +Distributed Electronic Mail Models + + There are three fundamental models of client/server email: offline, + online, and disconnected use. IMAP4 can be used in any one of these + three models. + + The offline model is the most familiar form of client/server email + today, and is used by protocols such as POP-3 (RFC 1225) and UUCP. + In this model, a client application periodically connects to a + server. It downloads all the pending messages to the client machine + and deletes these from the server. Thereafter, all mail processing + is local to the client. This model is store-and-forward; it moves + mail on demand from an intermediate server (maildrop) to a single + destination machine. + + The online model is most commonly used with remote filesystem + protocols such as NFS. In this model, a client application + manipulates mailbox data on a server machine. A connection to the + server is maintained throughout the session. No mailbox data are + kept on the client; the client retrieves data from the server as is + needed. IMAP4 introduces a form of the online model that requires + considerably less network bandwidth than a remote filesystem + protocol, and provides the opportunity for using the server for CPU + or I/O intensive functions such as parsing and searching. + + The disconnected use model is a hybrid of the offline and online + models, and is used by protocols such as PCMAIL (RFC 1056). In this + model, a client user downloads some set of messages from the server, + manipulates them offline, then at some later time uploads the + changes. The server remains the authoritative repository of the + messages. The problems of synchronization (particularly when + multiple clients are involved) are handled through the means of + unique identifiers for each message. + + + +Crispin [Page 1] + +RFC 1733 IMAP4 - Model December 1994 + + + Each of these models have their own strengths and weaknesses: + + Feature Offline Online Disc + ------- ------- ------ ---- + Can use multiple clients NO YES YES + Minimum use of server connect time YES NO YES + Minimum use of server resources YES NO NO + Minimum use of client disk resources NO YES NO + Multiple remote mailboxes NO YES YES + Fast startup NO YES NO + Mail processing when not online YES NO YES + + Although IMAP4 has its origins as a protocol designed to accommodate + the online model, it can support the other two models as well. This + makes possible the creation of clients that can be used in any of the + three models. For example, a user may wish to switch between the + online and disconnected models on a regular basis (e.g. owing to + travel). + + IMAP4 is designed to transmit message data on demand, and to provide + the facilities necessary for a client to decide what data it needs at + any particular time. There is generally no need to do a wholesale + transfer of an entire mailbox or even of the complete text of a + message. This makes a difference in situations where the mailbox is + large, or when the link to the server is slow. + + More specifically, IMAP4 supports server-based RFC 822 and MIME + processing. With this information, it is possible for a client to + determine in advance whether it wishes to retrieve a particular + message or part of a message. For example, a user connected to an + IMAP4 server via a dialup link can determine that a message has a + 2000 byte text segment and a 40 megabyte video segment, and elect to + fetch only the text segment. + + In IMAP4, the client/server relationship lasts only for the duration + of the TCP connection. There is no registration of clients. Except + for any unique identifiers used in disconnected use operation, the + client initially has no knowledge of mailbox state and learns it from + the IMAP4 server when a mailbox is selected. This initial transfer + is minimal; the client requests additional state data as it needs. + + As noted above, the choice for the location of mailbox data depends + upon the model chosen. The location of message state (e.g. whether + or not a message has been read or answered) is also determined by the + model, and is not necessarily the same as the location of the mailbox + data. For example, in the online model message state can be co- + located with mailbox data; it can also be located elsewhere (on the + client or on a third agent) using unique identifiers to achieve + + + +Crispin [Page 2] + +RFC 1733 IMAP4 - Model December 1994 + + + common reference across sessions. The latter is particularly useful + with a server that exports public data such as netnews and does not + maintain per-user state. + + The IMAP4 protocol provides the generality to implement these + different models. This is done by means of server and (especially) + client configuration, and not by requiring changes to the protocol or + the implementation of the protocol. + + +Security Considerations + + Security issues are not discussed in this memo. + + +Author's Address: + + Mark R. Crispin + Networks and Distributed Computing, JE-30 + University of Washington + Seattle, WA 98195 + + Phone: (206) 543-5762 + + EMail: MRC@CAC.Washington.EDU + + + + + + + + + + + + + + + + + + + + + + + + + + +Crispin [Page 3] + diff --git a/imap/docs/rfc/rfc2061.txt b/imap/docs/rfc/rfc2061.txt new file mode 100644 index 00000000..7cb02bb2 --- /dev/null +++ b/imap/docs/rfc/rfc2061.txt @@ -0,0 +1,171 @@ + + + + + + +Network Working Group M. Crispin +Request for Comments: 2061 University of Washington +Category: Informational December 1996 + + + IMAP4 COMPATIBILITY WITH IMAP2BIS + +Status of this Memo + + This memo provides information for the Internet community. This memo + does not specify an Internet standard of any kind. Distribution of + this memo is unlimited. + +Introduction + + The Internet Message Access Protocol (IMAP) has been through several + revisions and variants in its 10-year history. Many of these are + either extinct or extremely rare; in particular, several undocumented + variants and the variants described in RFC 1064, RFC 1176, and RFC + 1203 fall into this category. + + One variant, IMAP2bis, is at the time of this writing very common and + has been widely distributed with the Pine mailer. Unfortunately, + there is no definite document describing IMAP2bis. This document is + intended to be read along with RFC 1176 and the most recent IMAP4 + specification (RFC 2060) to assist implementors in creating an IMAP4 + implementation to interoperate with implementations that conform to + earlier specifications. Nothing in this document is required by the + IMAP4 specification; implementors must decide for themselves whether + they want their implementation to fail if it encounters old software. + + At the time of this writing, IMAP4 has been updated from the version + described in RFC 1730. An implementor who wishes to interoperate + with both RFC 1730 and RFC 2060 should refer to both documents. + + This information is not complete; it reflects current knowledge of + server and client implementations as well as "folklore" acquired in + the evolution of the protocol. It is NOT a description of how to + interoperate with all variants of IMAP, but rather with the old + variant that is most likely to be encountered. For detailed + information on interoperating with other old variants, refer to RFC + 1732. + +IMAP4 client interoperability with IMAP2bis servers + + A quick way to check whether a server implementation supports the + IMAP4 specification is to try the CAPABILITY command. An OK response + will indicate which variant(s) of IMAP4 are supported by the server. + + + +Crispin Informational [Page 1] + +RFC 2061 IMAP4 Compatibility December 1996 + + + If the client does not find any of its known variant in the response, + it should treat the server as IMAP2bis. A BAD response indicates an + IMAP2bis or older server. + + Most IMAP4 facilities are in IMAP2bis. The following exceptions + exist: + + CAPABILITY command + The absense of this command indicates IMAP2bis (or older). + + AUTHENTICATE command. + Use the LOGIN command. + + LSUB, SUBSCRIBE, and UNSUBSCRIBE commands + No direct functional equivalent. IMAP2bis had a concept + called "bboards" which is not in IMAP4. RFC 1176 supported + these with the BBOARD and FIND BBOARDS commands. IMAP2bis + augmented these with the FIND ALL.BBOARDS, SUBSCRIBE BBOARD, + and UNSUBSCRIBE BBOARD commands. It is recommended that + none of these commands be implemented in new software, + including servers that support old clients. + + LIST command + Use the command FIND ALL.MAILBOXES, which has a similar syn- + tax and response to the FIND MAILBOXES command described in + RFC 1176. The FIND MAILBOXES command is unlikely to produce + useful information. + + * in a sequence + Use the number of messages in the mailbox from the EXISTS + unsolicited response. + + SEARCH extensions (character set, additional criteria) + Reformulate the search request using only the RFC 1176 syn- + tax. This may entail doing multiple searches to achieve the + desired results. + + BODYSTRUCTURE fetch data item + Use the non-extensible BODY data item. + + body sections HEADER, TEXT, MIME, HEADER.FIELDS, HEADER.FIELDS.NOT + Use body section numbers only. + + BODY.PEEK[section] + Use BODY[section] and manually clear the \Seen flag as + necessary. + + + + + +Crispin Informational [Page 2] + +RFC 2061 IMAP4 Compatibility December 1996 + + + FLAGS.SILENT, +FLAGS.SILENT, and -FLAGS.SILENT store data items + Use the corresponding non-SILENT versions and ignore the + untagged FETCH responses which come back. + + UID fetch data item and the UID commands + No functional equivalent. + + CLOSE command + No functional equivalent. + + + In IMAP2bis, the TRYCREATE special information token is sent as a + separate unsolicited OK response instead of inside the NO response. + + IMAP2bis is ambiguous about whether or not flags or internal dates + are preserved on COPY. It is impossible to know what behavior is + supported by the server. + +IMAP4 server interoperability with IMAP2bis clients + + The only interoperability problem between an IMAP4 server and a + well-written IMAP2bis client is an incompatibility with the use of + "\" in quoted strings. This is best avoided by using literals + instead of quoted strings if "\" or <"> is embedded in the string. + +Security Considerations + + Security issues are not discussed in this memo. + +Author's Address + + Mark R. Crispin + Networks and Distributed Computing + University of Washington + 4545 15th Aveneue NE + Seattle, WA 98105-4527 + + Phone: (206) 543-5762 + EMail: MRC@CAC.Washington.EDU + + + + + + + + + + + + +Crispin Informational [Page 3] + diff --git a/imap/docs/rfc/rfc2062.txt b/imap/docs/rfc/rfc2062.txt new file mode 100644 index 00000000..865d1dad --- /dev/null +++ b/imap/docs/rfc/rfc2062.txt @@ -0,0 +1,451 @@ + + + + + + +Network Working Group M. Crispin +Request for Comments: 2062 University of Washington +Category: Informational December 1996 + + + Internet Message Access Protocol - Obsolete Syntax + +Status of this Memo + + This memo provides information for the Internet community. This memo + does not specify an Internet standard of any kind. Distribution of + this memo is unlimited. + +Abstract + + This document describes obsolete syntax which may be encountered by + IMAP4 implementations which deal with older versions of the Internet + Mail Access Protocol. IMAP4 implementations MAY implement this + syntax in order to maximize interoperability with older + implementations. + + This document repeats information from earlier documents, most + notably RFC 1176 and RFC 1730. + +Obsolete Commands and Fetch Data Items + + The following commands are OBSOLETE. It is NOT required to support + any of these commands or fetch data items in new server + implementations. These commands are documented here for the benefit + of implementors who may wish to support them for compatibility with + old client implementations. + + The section headings of these commands are intended to correspond + with where they would be located in the main document if they were + not obsoleted. + +6.3.OBS.1. FIND ALL.MAILBOXES Command + + Arguments: mailbox name with possible wildcards + + Data: untagged responses: MAILBOX + + Result: OK - find completed + NO - find failure: can't list that name + BAD - command unknown or arguments invalid + + + + + + +Crispin Informational [Page 1] + +RFC 2062 IMAP4 Obsolete December 1996 + + + The FIND ALL.MAILBOXES command returns a subset of names from the + complete set of all names available to the user. It returns zero + or more untagged MAILBOX replies. The mailbox argument to FIND + ALL.MAILBOXES is similar to that for LIST with an empty reference, + except that the characters "%" and "?" match a single character. + + Example: C: A002 FIND ALL.MAILBOXES * + S: * MAILBOX blurdybloop + S: * MAILBOX INBOX + S: A002 OK FIND ALL.MAILBOXES completed + +6.3.OBS.2. FIND MAILBOXES Command + + Arguments: mailbox name with possible wildcards + + Data: untagged responses: MAILBOX + + Result: OK - find completed + NO - find failure: can't list that name + BAD - command unknown or arguments invalid + + The FIND MAILBOXES command returns a subset of names from the set + of names that the user has declared as being "active" or + "subscribed". It returns zero or more untagged MAILBOX replies. + The mailbox argument to FIND MAILBOXES is similar to that for LSUB + with an empty reference, except that the characters "%" and "?" + match a single character. + + Example: C: A002 FIND MAILBOXES * + S: * MAILBOX blurdybloop + S: * MAILBOX INBOX + S: A002 OK FIND MAILBOXES completed + +6.3.OBS.3. SUBSCRIBE MAILBOX Command + + Arguments: mailbox name + + Data: no specific data for this command + + Result: OK - subscribe completed + NO - subscribe failure: can't subscribe to that name + BAD - command unknown or arguments invalid + + The SUBSCRIBE MAILBOX command is identical in effect to the + SUBSCRIBE command. A server which implements this command must be + able to distinguish between a SUBSCRIBE MAILBOX command and a + SUBSCRIBE command with a mailbox name argument of "MAILBOX". + + + + +Crispin Informational [Page 2] + +RFC 2062 IMAP4 Obsolete December 1996 + + + Example: C: A002 SUBSCRIBE MAILBOX #news.comp.mail.mime + S: A002 OK SUBSCRIBE MAILBOX to #news.comp.mail.mime + completed + C: A003 SUBSCRIBE MAILBOX + S: A003 OK SUBSCRIBE to MAILBOX completed + + +6.3.OBS.4. UNSUBSCRIBE MAILBOX Command + + Arguments: mailbox name + + Data: no specific data for this command + + Result: OK - unsubscribe completed + NO - unsubscribe failure: can't unsubscribe that name + BAD - command unknown or arguments invalid + + The UNSUBSCRIBE MAILBOX command is identical in effect to the + UNSUBSCRIBE command. A server which implements this command must + be able to distinguish between a UNSUBSCRIBE MAILBOX command and + an UNSUBSCRIBE command with a mailbox name argument of "MAILBOX". + + Example: C: A002 UNSUBSCRIBE MAILBOX #news.comp.mail.mime + S: A002 OK UNSUBSCRIBE MAILBOX from #news.comp.mail.mime + completed + C: A003 UNSUBSCRIBE MAILBOX + S: A003 OK UNSUBSCRIBE from MAILBOX completed + +6.4.OBS.1 PARTIAL Command + + Arguments: message sequence number + message data item name + position of first octet + number of octets + + Data: untagged responses: FETCH + + Result: OK - partial completed + NO - partial error: can't fetch that data + BAD - command unknown or arguments invalid + + The PARTIAL command is equivalent to the associated FETCH command, + with the added functionality that only the specified number of + octets, beginning at the specified starting octet, are returned. + Only a single message can be fetched at a time. The first octet + of a message, and hence the minimum for the starting octet, is + octet 1. + + + + +Crispin Informational [Page 3] + +RFC 2062 IMAP4 Obsolete December 1996 + + + The following FETCH items are valid data for PARTIAL: RFC822, + RFC822.HEADER, RFC822.TEXT, BODY[<section>], as well as any .PEEK + forms of these. + + Any partial fetch that attempts to read beyond the end of the text + is truncated as appropriate. If the starting octet is beyond the + end of the text, an empty string is returned. + + The data are returned with the FETCH response. There is no + indication of the range of the partial data in this response. It + is not possible to stream multiple PARTIAL commands of the same + data item without processing and synchronizing at each step, since + streamed commands may be executed out of order. + + There is no requirement that partial fetches follow any sequence. + For example, if a partial fetch of octets 1 through 10000 breaks + in an awkward place for BASE64 decoding, it is permitted to + continue with a partial fetch of 9987 through 19987, etc. + + The handling of the \Seen flag is the same as in the associated + FETCH command. + + Example: C: A005 PARTIAL 4 RFC822 1 1024 + S: * 1 FETCH (RFC822 {1024} + S: Return-Path: <gray@cac.washington.edu> + S: ... + S: ......... FLAGS (\Seen)) + S: A005 OK PARTIAL completed + +6.4.5.OBS.1 Obsolete FETCH Data Items + + The following FETCH data items are obsolete: + + BODY[<...>0] A body part number of 0 is the [RFC-822] header of + the message. BODY[0] is functionally equivalent to + BODY[HEADER], differing in the syntax of the + resulting untagged FETCH data (BODY[0] is + returned). + + RFC822.HEADER.LINES <header_list> + Functionally equivalent to BODY.PEEK[HEADER.LINES + <header_list>], differing in the syntax of the + resulting untagged FETCH data (RFC822.HEADER is + returned). + + + + + + + +Crispin Informational [Page 4] + +RFC 2062 IMAP4 Obsolete December 1996 + + + RFC822.HEADER.LINES.NOT <header_list> + Functionally equivalent to + BODY.PEEK[HEADER.LINES.NOT <header_list>], + differing in the syntax of the resulting untagged + FETCH data (RFC822.HEADER is returned). + + RFC822.PEEK Functionally equivalent to BODY.PEEK[], except for + the syntax of the resulting untagged FETCH data + (RFC822 is returned). + + RFC822.TEXT.PEEK + Functionally equivalent to BODY.PEEK[TEXT], except + for the syntax of the resulting untagged FETCH data + (RFC822.TEXT is returned). + +Obsolete Responses + + The following responses are OBSOLETE. Except as noted below, these + responses MUST NOT be transmitted by new server implementations. + Client implementations SHOULD accept these responses. + + The section headings of these responses are intended to correspond + with where they would be located in the main document if they were + not obsoleted. + +7.2.OBS.1. MAILBOX Response + + Data: name + + The MAILBOX response MUST NOT be transmitted by server + implementations except in response to the obsolete FIND MAILBOXES + and FIND ALL.MAILBOXES commands. Client implementations that do + not use these commands MAY ignore this response. It is documented + here for the benefit of implementors who may wish to support it + for compatibility with old client implementations. + + This response occurs as a result of the FIND MAILBOXES and FIND + ALL.MAILBOXES commands. It returns a single name that matches the + FIND specification. There are no attributes or hierarchy + delimiter. + + Example: S: * MAILBOX blurdybloop + + + + + + + + + +Crispin Informational [Page 5] + +RFC 2062 IMAP4 Obsolete December 1996 + + +7.3.OBS.1. COPY Response + + Data: none + + The COPY response MUST NOT be transmitted by new server + implementations. Client implementations MUST ignore the COPY + response. It is documented here for the benefit of client + implementors who may encounter this response from old server + implementations. + + In some experimental versions of this protocol, this response was + returned in response to a COPY command to indicate on a + per-message basis that the message was copied successfully. + + Example: S: * 44 COPY + +7.3.OBS.2. STORE Response + + Data: message data + + The STORE response MUST NOT be transmitted by new server + implementations. Client implementations MUST treat the STORE + response as equivalent to the FETCH response. It is documented + here for the benefit of client implementors who may encounter this + response from old server implementations. + + In some experimental versions of this protocol, this response was + returned instead of FETCH in response to a STORE command to report + the new value of the flags. + + Example: S: * 69 STORE (FLAGS (\Deleted)) + +Formal Syntax of Obsolete Commands and Responses + + Each obsolete syntax rule that is suffixed with "_old" is added to + the corresponding name in the formal syntax. For example, + command_auth_old adds the FIND command to command_auth. + + command_auth_old ::= find + + command_select_old + ::= partial + + date_year_old ::= 2digit + ;; (year - 1900) + + date_time_old ::= <"> date_day_fixed "-" date_month "-" date_year + SPACE time "-" zone_name <"> + + + +Crispin Informational [Page 6] + +RFC 2062 IMAP4 Obsolete December 1996 + + + find ::= "FIND" SPACE ["ALL."] "MAILBOXES" SPACE + list_mailbox + + fetch_att_old ::= "RFC822.HEADER.LINES" [".NOT"] SPACE header_list / + fetch_text_old + + fetch_text_old ::= "BODY" [".PEEK"] section_old / + "RFC822" [".HEADER" / ".TEXT" [".PEEK"]] + + msg_data_old ::= "COPY" / ("STORE" SPACE msg_att) + + partial ::= "PARTIAL" SPACE nz_number SPACE fetch_text_old SPACE + number SPACE number + + section_old ::= "[" (number ["." number]) "]" + + subscribe_old ::= "SUBSCRIBE" SPACE "MAILBOX" SPACE mailbox + + unsubscribe_old ::= "UNSUBSCRIBE" SPACE "MAILBOX" SPACE mailbox + + zone_name ::= "UT" / "GMT" / "Z" / ;; +0000 + "AST" / "EDT" / ;; -0400 + "EST" / "CDT" / ;; -0500 + "CST" / "MDT" / ;; -0600 + "MST" / "PDT" / ;; -0700 + "PST" / "YDT" / ;; -0800 + "YST" / "HDT" / ;; -0900 + "HST" / "BDT" / ;; -1000 + "BST" / ;; -1100 + "A" / "B" / "C" / "D" / "E" / "F" / ;; +1 to +6 + "G" / "H" / "I" / "K" / "L" / "M" / ;; +7 to +12 + "N" / "O" / "P" / "Q" / "R" / "S" / ;; -1 to -6 + "T" / "U" / "V" / "W" / "X" / "Y" ;; -7 to -12 + +Security Considerations + + Security issues are not discussed in this memo. + + + + + + + + + + + + + + +Crispin Informational [Page 7] + +RFC 2062 IMAP4 Obsolete December 1996 + + +Author's Address + + Mark R. Crispin + Networks and Distributed Computing + University of Washington + 4545 15th Aveneue NE + Seattle, WA 98105-4527 + + Phone: (206) 543-5762 + EMail: MRC@CAC.Washington.EDU + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Crispin Informational [Page 8] + diff --git a/imap/docs/rfc/rfc2087.txt b/imap/docs/rfc/rfc2087.txt new file mode 100644 index 00000000..1db5b57b --- /dev/null +++ b/imap/docs/rfc/rfc2087.txt @@ -0,0 +1,283 @@ + + + + + + +Network Working Group J. Myers +Request for Comments: 2087 Carnegie Mellon +Category: Standards Track January 1997 + + + IMAP4 QUOTA extension + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +1. Abstract + + The QUOTA extension of the Internet Message Access Protocol [IMAP4] + permits administrative limits on resource usage (quotas) to be + manipulated through the IMAP protocol. + +Table of Contents + + 1. Abstract........................................... 1 + 2. Conventions Used in this Document.................. 1 + 3. Introduction and Overview.......................... 2 + 4. Commands........................................... 2 + 4.1. SETQUOTA Command................................... 2 + 4.2. GETQUOTA Command................................... 2 + 4.3. GETQUOTAROOT Command............................... 3 + 5. Responses.......................................... 3 + 5.1. QUOTA Response..................................... 3 + 5.2. QUOTAROOT Response................................. 4 + 6. Formal syntax...................................... 4 + 7. References......................................... 5 + 8. Security Considerations............................ 5 + 9. Author's Address................................... 5 + + +2. Conventions Used in this Document + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. + + + + + + + + +Myers Standards Track [Page 1] + +RFC 2087 QUOTA January 1997 + + +3. Introduction and Overview + + The QUOTA extension is present in any IMAP4 implementation which + returns "QUOTA" as one of the supported capabilities to the + CAPABILITY command. + + An IMAP4 server which supports the QUOTA capability may support + limits on any number of resources. Each resource has an atom name + and an implementation-defined interpretation which evaluates to an + integer. Examples of such resources are: + + Name Interpretation + + STORAGE Sum of messages' RFC822.SIZE, in units of 1024 octets + MESSAGE Number of messages + + + Each mailbox has zero or more implementation-defined named "quota + roots". Each quota root has zero or more resource limits. All + mailboxes that share the same named quota root share the resource + limits of the quota root. + + Quota root names do not necessarily have to match the names of + existing mailboxes. + +4. Commands + +4.1. SETQUOTA Command + + Arguments: quota root + list of resource limits + + Data: untagged responses: QUOTA + + Result: OK - setquota completed + NO - setquota error: can't set that data + BAD - command unknown or arguments invalid + + The SETQUOTA command takes the name of a mailbox quota root and a + list of resource limits. The resource limits for the named quota root + are changed to be the specified limits. Any previous resource limits + for the named quota root are discarded. + + If the named quota root did not previously exist, an implementation + may optionally create it and change the quota roots for any number of + existing mailboxes in an implementation-defined manner. + + + + + +Myers Standards Track [Page 2] + +RFC 2087 QUOTA January 1997 + + + Example: C: A001 SETQUOTA "" (STORAGE 512) + S: * QUOTA "" (STORAGE 10 512) + S: A001 OK Setquota completed + +4.2. GETQUOTA Command + + Arguments: quota root + + Data: untagged responses: QUOTA + + Result: OK - getquota completed + NO - getquota error: no such quota root, permission + denied + BAD - command unknown or arguments invalid + + The GETQUOTA command takes the name of a quota root and returns the + quota root's resource usage and limits in an untagged QUOTA response. + + Example: C: A003 GETQUOTA "" + S: * QUOTA "" (STORAGE 10 512) + S: A003 OK Getquota completed + +4.3. GETQUOTAROOT Command + + Arguments: mailbox name + + Data: untagged responses: QUOTAROOT, QUOTA + + Result: OK - getquota completed + NO - getquota error: no such mailbox, permission denied + BAD - command unknown or arguments invalid + + The GETQUOTAROOT command takes the name of a mailbox and returns the + list of quota roots for the mailbox in an untagged QUOTAROOT + response. For each listed quota root, it also returns the quota + root's resource usage and limits in an untagged QUOTA response. + + Example: C: A003 GETQUOTAROOT INBOX + S: * QUOTAROOT INBOX "" + S: * QUOTA "" (STORAGE 10 512) + S: A003 OK Getquota completed + + + + + + + + + + +Myers Standards Track [Page 3] + +RFC 2087 QUOTA January 1997 + + +5. Responses + +5.1. QUOTA Response + + Data: quota root name + list of resource names, usages, and limits + + This response occurs as a result of a GETQUOTA or GETQUOTAROOT + command. The first string is the name of the quota root for which + this quota applies. + + The name is followed by a S-expression format list of the resource + usage and limits of the quota root. The list contains zero or + more triplets. Each triplet conatins a resource name, the current + usage of the resource, and the resource limit. + + Resources not named in the list are not limited in the quota root. + Thus, an empty list means there are no administrative resource + limits in the quota root. + + Example: S: * QUOTA "" (STORAGE 10 512) + +5.2. QUOTAROOT Response + + Data: mailbox name + zero or more quota root names + + This response occurs as a result of a GETQUOTAROOT command. The + first string is the mailbox and the remaining strings are the + names of the quota roots for the mailbox. + + Example: S: * QUOTAROOT INBOX "" + S: * QUOTAROOT comp.mail.mime + +6. Formal syntax + + The following syntax specification uses the augmented Backus-Naur + Form (BNF) notation as specified in RFC 822 with one exception; the + delimiter used with the "#" construct is a single space (SP) and not + one or more commas. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper or lower case characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + + + + + +Myers Standards Track [Page 4] + +RFC 2087 QUOTA January 1997 + + + getquota ::= "GETQUOTA" SP astring + + getquotaroot ::= "GETQUOTAROOT" SP astring + + quota_list ::= "(" #quota_resource ")" + + quota_resource ::= atom SP number SP number + + quota_response ::= "QUOTA" SP astring SP quota_list + + quotaroot_response + ::= "QUOTAROOT" SP astring *(SP astring) + + setquota ::= "SETQUOTA" SP astring SP setquota_list + + setquota_list ::= "(" 0#setquota_resource ")" + + setquota_resource ::= atom SP number + +7. References + + [IMAP4] Crispin, M., "Internet Message Access Protocol - Version 4", + RFC 1730, University of Washington, December 1994. + + [RFC-822] Crocker, D., "Standard for the Format of ARPA Internet + Text Messages", STD 11, RFC 822. + +8. Security Considerations + + Implementors should be careful to make sure the implementation of + these commands does not violate the site's security policy. The + resource usage of other users is likely to be considered confidential + information and should not be divulged to unauthorized persons. + +9. Author's Address + + John G. Myers + Carnegie-Mellon University + 5000 Forbes Ave. + Pittsburgh PA, 15213-3890 + + EMail: jgm+@cmu.edu + + + + + + + + + +Myers Standards Track [Page 5] + diff --git a/imap/docs/rfc/rfc2088.txt b/imap/docs/rfc/rfc2088.txt new file mode 100644 index 00000000..f36cc764 --- /dev/null +++ b/imap/docs/rfc/rfc2088.txt @@ -0,0 +1,115 @@ + + + + + + +Network Working Group J. Myers +Request for Comments: 2088 Carnegie Mellon +Cateogry: Standards Track January 1997 + + + IMAP4 non-synchronizing literals + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +1. Abstract + + The Internet Message Access Protocol [IMAP4] contains the "literal" + syntactic construct for communicating strings. When sending a + literal from client to server, IMAP4 requires the client to wait for + the server to send a command continuation request between sending the + octet count and the string data. This document specifies an + alternate form of literal which does not require this network round + trip. + +2. Conventions Used in this Document + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. + +3. Specification + + The non-synchronizing literal is added an alternate form of literal, + and may appear in communication from client to server instead of the + IMAP4 form of literal. The IMAP4 form of literal, used in + communication from client to server, is referred to as a + synchronizing literal. + + Non-synchronizing literals may be used with any IMAP4 server + implementation which returns "LITERAL+" as one of the supported + capabilities to the CAPABILITY command. If the server does not + advertise the LITERAL+ capability, the client must use synchronizing + literals instead. + + The non-synchronizing literal is distinguished from the original + synchronizing literal by having a plus ('+') between the octet count + and the closing brace ('}'). The server does not generate a command + continuation request in response to a non-synchronizing literal, and + + + +Myers Standards Track [Page 1] + +RFC 2088 LITERAL January 1997 + + + clients are not required to wait before sending the octets of a non- + synchronizing literal. + + The protocol receiver of an IMAP4 server must check the end of every + received line for an open brace ('{') followed by an octet count, a + plus ('+'), and a close brace ('}') immediately preceeding the CRLF. + If it finds this sequence, it is the octet count of a non- + synchronizing literal and the server MUST treat the specified number + of following octets and the following line as part of the same + command. A server MAY still process commands and reject errors on a + line-by-line basis, as long as it checks for non-synchronizing + literals at the end of each line. + + Example: C: A001 LOGIN {11+} + C: FRED FOOBAR {7+} + C: fat man + S: A001 OK LOGIN completed + +4. Formal Syntax + + The following syntax specification uses the augmented Backus-Naur + Form (BNF) notation as specified in [RFC-822] as modified by [IMAP4]. + Non-terminals referenced but not defined below are as defined by + [IMAP4]. + + literal ::= "{" number ["+"] "}" CRLF *CHAR8 + ;; Number represents the number of CHAR8 octets + +6. References + + [IMAP4] Crispin, M., "Internet Message Access Protocol - Version 4", + draft-crispin-imap-base-XX.txt, University of Washington, April 1996. + + [RFC-822] Crocker, D., "Standard for the Format of ARPA Internet Text + Messages", STD 11, RFC 822. + +7. Security Considerations + + There are no known security issues with this extension. + +8. Author's Address + + John G. Myers + Carnegie-Mellon University + 5000 Forbes Ave. + Pittsburgh PA, 15213-3890 + + Email: jgm+@cmu.edu + + + +Myers Standards Track [Page 2] + diff --git a/imap/docs/rfc/rfc2177.txt b/imap/docs/rfc/rfc2177.txt new file mode 100644 index 00000000..c11c7654 --- /dev/null +++ b/imap/docs/rfc/rfc2177.txt @@ -0,0 +1,227 @@ + + + + + + +Network Working Group B. Leiba +Request for Comments: 2177 IBM T.J. Watson Research Center +Category: Standards Track June 1997 + + + IMAP4 IDLE command + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +1. Abstract + + The Internet Message Access Protocol [IMAP4] requires a client to + poll the server for changes to the selected mailbox (new mail, + deletions). It's often more desirable to have the server transmit + updates to the client in real time. This allows a user to see new + mail immediately. It also helps some real-time applications based on + IMAP, which might otherwise need to poll extremely often (such as + every few seconds). (While the spec actually does allow a server to + push EXISTS responses aysynchronously, a client can't expect this + behaviour and must poll.) + + This document specifies the syntax of an IDLE command, which will + allow a client to tell the server that it's ready to accept such + real-time updates. + +2. Conventions Used in this Document + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. + + The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" + in this document are to be interpreted as described in RFC 2060 + [IMAP4]. + +3. Specification + + IDLE Command + + Arguments: none + + Responses: continuation data will be requested; the client sends + the continuation data "DONE" to end the command + + + +Leiba Standards Track [Page 1] + +RFC 2177 IMAP4 IDLE command June 1997 + + + + Result: OK - IDLE completed after client sent "DONE" + NO - failure: the server will not allow the IDLE + command at this time + BAD - command unknown or arguments invalid + + The IDLE command may be used with any IMAP4 server implementation + that returns "IDLE" as one of the supported capabilities to the + CAPABILITY command. If the server does not advertise the IDLE + capability, the client MUST NOT use the IDLE command and must poll + for mailbox updates. In particular, the client MUST continue to be + able to accept unsolicited untagged responses to ANY command, as + specified in the base IMAP specification. + + The IDLE command is sent from the client to the server when the + client is ready to accept unsolicited mailbox update messages. The + server requests a response to the IDLE command using the continuation + ("+") response. The IDLE command remains active until the client + responds to the continuation, and as long as an IDLE command is + active, the server is now free to send untagged EXISTS, EXPUNGE, and + other messages at any time. + + The IDLE command is terminated by the receipt of a "DONE" + continuation from the client; such response satisfies the server's + continuation request. At that point, the server MAY send any + remaining queued untagged responses and then MUST immediately send + the tagged response to the IDLE command and prepare to process other + commands. As in the base specification, the processing of any new + command may cause the sending of unsolicited untagged responses, + subject to the ambiguity limitations. The client MUST NOT send a + command while the server is waiting for the DONE, since the server + will not be able to distinguish a command from a continuation. + + The server MAY consider a client inactive if it has an IDLE command + running, and if such a server has an inactivity timeout it MAY log + the client off implicitly at the end of its timeout period. Because + of that, clients using IDLE are advised to terminate the IDLE and + re-issue it at least every 29 minutes to avoid being logged off. + This still allows a client to receive immediate mailbox updates even + though it need only "poll" at half hour intervals. + + + + + + + + + + + +Leiba Standards Track [Page 2] + +RFC 2177 IMAP4 IDLE command June 1997 + + + Example: C: A001 SELECT INBOX + S: * FLAGS (Deleted Seen) + S: * 3 EXISTS + S: * 0 RECENT + S: * OK [UIDVALIDITY 1] + S: A001 OK SELECT completed + C: A002 IDLE + S: + idling + ...time passes; new mail arrives... + S: * 4 EXISTS + C: DONE + S: A002 OK IDLE terminated + ...another client expunges message 2 now... + C: A003 FETCH 4 ALL + S: * 4 FETCH (...) + S: A003 OK FETCH completed + C: A004 IDLE + S: * 2 EXPUNGE + S: * 3 EXISTS + S: + idling + ...time passes; another client expunges message 3... + S: * 3 EXPUNGE + S: * 2 EXISTS + ...time passes; new mail arrives... + S: * 3 EXISTS + C: DONE + S: A004 OK IDLE terminated + C: A005 FETCH 3 ALL + S: * 3 FETCH (...) + S: A005 OK FETCH completed + C: A006 IDLE + +4. Formal Syntax + + The following syntax specification uses the augmented Backus-Naur + Form (BNF) notation as specified in [RFC-822] as modified by [IMAP4]. + Non-terminals referenced but not defined below are as defined by + [IMAP4]. + + command_auth ::= append / create / delete / examine / list / lsub / + rename / select / status / subscribe / unsubscribe + / idle + ;; Valid only in Authenticated or Selected state + + idle ::= "IDLE" CRLF "DONE" + + + + + + +Leiba Standards Track [Page 3] + +RFC 2177 IMAP4 IDLE command June 1997 + + +5. References + + [IMAP4] Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 2060, December 1996. + +6. Security Considerations + + There are no known security issues with this extension. + +7. Author's Address + + Barry Leiba + IBM T.J. Watson Research Center + 30 Saw Mill River Road + Hawthorne, NY 10532 + + Email: leiba@watson.ibm.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Leiba Standards Track [Page 4] + diff --git a/imap/docs/rfc/rfc2180.txt b/imap/docs/rfc/rfc2180.txt new file mode 100644 index 00000000..57607002 --- /dev/null +++ b/imap/docs/rfc/rfc2180.txt @@ -0,0 +1,787 @@ + + + + + + +Network Working Group M. Gahrns +Request for Comments: 2180 Microsoft +Category: Informational July 1997 + + + IMAP4 Multi-Accessed Mailbox Practice + +Status of this Memo + + This memo provides information for the Internet community. This memo + does not specify an Internet standard of any kind. Distribution of + this memo is unlimited. + +1. Abstract + + IMAP4[RFC-2060] is rich client/server protocol that allows a client + to access and manipulate electronic mail messages on a server. + Within the protocol framework, it is possible to have differing + results for particular client/server interactions. If a protocol does + not allow for this, it is often unduly restrictive. + + For example, when multiple clients are accessing a mailbox and one + attempts to delete the mailbox, an IMAP4 server may choose to + implement a solution based upon server architectural constraints or + individual preference. + + With this flexibility comes greater client responsibility. It is not + sufficient for a client to be written based upon the behavior of a + particular IMAP server. Rather the client must be based upon the + behavior allowed by the protocol. + + By documenting common IMAP4 server practice for the case of + simultaneous client access to a mailbox, we hope to ensure the widest + amount of inter-operation between IMAP4 clients and servers. + + The behavior described in this document reflects the practice of some + existing servers or behavior that the consensus of the IMAP mailing + list has deemed to be reasonable. The behavior described within this + document is believed to be [RFC-2060] compliant. However, this + document is not meant to define IMAP4 compliance, nor is it an + exhaustive list of valid IMAP4 behavior. [RFC-2060] must always be + consulted to determine IMAP4 compliance, especially for server + behavior not described within this document. + + + + + + + + +Gahrns Informational [Page 1] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + +2. Conventions used in this document + + In examples,"C1:", "C2:" and "C3:" indicate lines sent by 3 different + clients (client #1, client #2 and client #3) that are connected to a + server. "S1:", "S2:" and "S3:" indicated lines sent by the server to + client #1, client #2 and client #3 respectively. + + A shared mailbox, is a mailbox that can be used by multiple users. + + A multi-accessed mailbox, is a mailbox that has multiple clients + simultaneously accessing it. + + A client is said to have accessed a mailbox after a successful SELECT + or EXAMINE command. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC-2119]. + + +3. Deletion/Renaming of a multi-accessed mailbox + + If an external agent or multiple clients are accessing a mailbox, + care must be taken when handling the deletion or renaming of the + mailbox. Following are some strategies an IMAP server may choose to + use when dealing with this situation. + + +3.1. The server MAY fail the DELETE/RENAME command of a multi-accessed + mailbox + + In some cases, this behavior may not be practical. For example, if a + large number of clients are accessing a shared mailbox, the window in + which no clients have the mailbox accessed may be small or non- + existent, effectively rendering the mailbox undeletable or + unrenamable. + + Example: + + <Client #1 and Client #2 have mailbox FOO accessed. Client #1 tries + to DELETE the mailbox and is refused> + + C1: A001 DELETE FOO + S1: A001 NO Mailbox FOO is in use by another user. + + + + + + + +Gahrns Informational [Page 2] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + +3.2. The server MAY allow the DELETE command of a multi-accessed + mailbox, but keep the information in the mailbox available for + those clients that currently have access to the mailbox. + + When all clients have finished accessing the mailbox, it is + permanently removed. For clients that do not already have access to + the mailbox, the 'ghosted' mailbox would not be available. For + example, it would not be returned to these clients in a subsequent + LIST or LSUB command and would not be a valid mailbox argument to any + other IMAP command until the reference count of clients accessing the + mailbox reached 0. + + In some cases, this behavior may not be desirable. For example if + someone created a mailbox with offensive or sensitive information, + one might prefer to have the mailbox deleted and all access to the + information contained within removed immediately, rather than + continuing to allow access until the client closes the mailbox. + + Furthermore, this behavior, may prevent 'recycling' of the same + mailbox name until all clients have finished accessing the original + mailbox. + + Example: + + <Client #1 and Client #2 have mailbox FOO selected. Client #1 DELETEs + mailbox FOO> + + C1: A001 DELETE FOO + S1: A001 OK Mailbox FOO is deleted. + + <Client #2 is still able to operate on the deleted mailbox> + + C2: B001 STORE 1 +FLAGS (\Seen) + S2: * 1 FETCH FLAGS (\Seen) + S2: B001 OK STORE completed + + <Client #3 which did not have access to the mailbox prior to the + deletion by client #1 does not have access to the mailbox> + + C3: C001 STATUS FOO (MESSAGES) + S3: C001 NO Mailbox does not exist + + <Nor is client #3 able to create a mailbox with the name FOO, while + the reference count is non zero> + + C3: C002 CREATE FOO + S3: C002 NO Mailbox FOO is still in use. Try again later. + + + + +Gahrns Informational [Page 3] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + + <Client #2 closes its access to the mailbox, no other clients have + access to the mailbox FOO and reference count becomes 0> + + C2: B002 CLOSE + S2: B002 OK CLOSE Completed + + <Now that the reference count on FOO has reached 0, the mailbox name + can be recycled> + + C3: C003 CREATE FOO + S3: C003 OK CREATE Completed + + +3.3. The server MAY allow the DELETE/RENAME of a multi-accessed + mailbox, but disconnect all other clients who have the mailbox + accessed by sending a untagged BYE response. + + A server may often choose to disconnect clients in the DELETE case, + but may choose to implement a "friendlier" method for the RENAME + case. + + Example: + + <Client #1 and Client #2 have mailbox FOO accessed. Client #1 DELETEs + the mailbox FOO> + + C1: A002 DELETE FOO + S1: A002 OK DELETE completed. + + <Server disconnects all other users of the mailbox> + S2: * BYE Mailbox FOO has been deleted. + + +3.4. The server MAY allow the RENAME of a multi-accessed mailbox by + simply changing the name attribute on the mailbox. + + Other clients that have access to the mailbox can continue issuing + commands such as FETCH that do not reference the mailbox name. + Clients would discover the renaming the next time they referred to + the old mailbox name. Some servers MAY choose to include the + [NEWNAME] response code in their tagged NO response to a command that + contained the old mailbox name, as a hint to the client that the + operation can succeed if the command is issued with the new mailbox + name. + + + + + + + +Gahrns Informational [Page 4] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + + Example: + + <Client #1 and Client #2 have mailbox FOO accessed. Client #1 RENAMEs + the mailbox.> + + C1: A001 RENAME FOO BAR + S1: A001 OK RENAME completed. + + <Client #2 is still able to do operations that do not reference the + mailbox name> + + C2: B001 FETCH 2:4 (FLAGS) + S2: * 2 FETCH . . . + S2: * 3 FETCH . . . + S2: * 4 FETCH . . . + S2: B001 OK FETCH completed + + <Client #2 is not able to do operations that reference the mailbox + name> + + C2: B002 APPEND FOO {300} C2: Date: Mon, 7 Feb 1994 + 21:52:25 0800 (PST) C2: . . . S2: B002 NO [NEWNAME FOO + BAR] Mailbox has been renamed + + +4. Expunging of messages on a multi-accessed mailbox + + If an external agent or multiple clients are accessing a mailbox, + care must be taken when handling the EXPUNGE of messages. Other + clients accessing the mailbox may be in the midst of issuing a + command that depends upon message sequence numbers. Because an + EXPUNGE response can not be sent while responding to a FETCH, STORE + or SEARCH command, it is not possible to immediately notify the + client of the EXPUNGE. This can result in ambiguity if the client + issues a FETCH, STORE or SEARCH operation on a message that has been + EXPUNGED. + + +4.1. Fetching of expunged messages + + Following are some strategies an IMAP server may choose to use when + dealing with a FETCH command on expunged messages. + + + + + + + + + +Gahrns Informational [Page 5] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + + Consider the following scenario: + + - Client #1 and Client #2 have mailbox FOO selected. + - There are 7 messages in the mailbox. + - Messages 4:7 are marked for deletion. + - Client #1 issues an EXPUNGE, to expunge messages 4:7 + + +4.1.1. The server MAY allow the EXPUNGE of a multi-accessed mailbox but + keep the messages available to satisfy subsequent FETCH commands + until it is able to send an EXPUNGE response to each client. + + In some cases, the behavior of keeping "ghosted" messages may not be + desirable. For example if a message contained offensive or sensitive + information, one might prefer to instantaneously remove all access to + the information, regardless of whether another client is in the midst + of accessing it. + + Example: (Building upon the scenario outlined in 4.1.) + + <Client #2 is still able to access the expunged messages because the + server has kept a 'ghosted' copy of the messages until it is able to + notify client #2 of the EXPUNGE> + + C2: B001 FETCH 4:7 RFC822 + S2: * 4 FETCH RFC822 . . . (RFC822 info returned) + S2: * 5 FETCH RFC822 . . . (RFC822 info returned) + S2: * 6 FETCH RFC822 . . . (RFC822 info returned) + S2: * 7 FETCH RFC822 . . . (RFC822 info returned) + S2: B001 OK FETCH Completed + + <Client #2 issues a command where it can get notified of the EXPUNGE> + + C2: B002 NOOP + S2: * 4 EXPUNGE + S2: * 4 EXPUNGE + S2: * 4 EXPUNGE + S2: * 4 EXPUNGE + S2: * 3 EXISTS + S2: B002 OK NOOP Complete + + <Client #2 no longer has access to the expunged messages> + + C2: B003 FETCH 4:7 RFC822 + S2: B003 NO Messages 4:7 are no longer available. + + + + + + +Gahrns Informational [Page 6] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + +4.1.2 The server MAY allow the EXPUNGE of a multi-accessed mailbox, + and on subsequent FETCH commands return FETCH responses only for + non-expunged messages and a tagged NO. + + After receiving a tagged NO FETCH response, the client SHOULD issue a + NOOP command so that it will be informed of any pending EXPUNGE + responses. The client may then either reissue the failed FETCH + command, or by examining the EXPUNGE response from the NOOP and the + FETCH response from the FETCH, determine that the FETCH failed + because of pending expunges. + + Example: (Building upon the scenario outlined in 4.1.) + + <Client #2 attempts to FETCH a mix of expunged and non-expunged + messages. A FETCH response is returned only for then non-expunged + messages along with a tagged NO> + + C2: B001 FETCH 3:5 ENVELOPE + S2: * 3 FETCH ENVELOPE . . . (ENVELOPE info returned) + S2: B001 NO Some of the requested messages no longer exist + + <Upon receiving a tagged NO FETCH response, Client #2 issues a NOOP + to be informed of any pending EXPUNGE responses> + + C2: B002 NOOP + S2: * 4 EXPUNGE + S2: * 4 EXPUNGE + S2: * 4 EXPUNGE + S2: * 4 EXPUNGE + S2: * 3 EXISTS + S2: B002 OK NOOP Completed. + + <By receiving a FETCH response for message 3, and an EXPUNGE response + that indicates messages 4:7 have been expunged, the client does not + need to re-issue the FETCH> + + + + + + + + + + + + + + + + +Gahrns Informational [Page 7] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + +4.1.3 The server MAY allow the EXPUNGE of a multi-accessed mailbox, and + on subsequent FETCH commands return the usual FETCH responses for + non-expunged messages, "NIL FETCH Responses" for expunged + messages, and a tagged OK response. + + If all of the messages in the subsequent FETCH command have been + expunged, the server SHOULD return only a tagged NO. In this case, + the client SHOULD issue a NOOP command so that it will be informed of + any pending EXPUNGE responses. The client may then either reissue + the failed FETCH command, or by examining the EXPUNGE response from + the NOOP, determine that the FETCH failed because of pending + expunges. + + "NIL FETCH responses" are a representation of empty data as + appropriate for the FETCH argument specified. + + Example: + + * 1 FETCH (ENVELOPE (NIL NIL NIL NIL NIL NIL NIL NIL NIL NIL)) + * 1 FETCH (FLAGS ()) + * 1 FETCH (INTERNALDATE "00-Jan-0000 00:00:00 +0000") + * 1 FETCH (RFC822 "") + * 1 FETCH (RFC822.HEADER "") + * 1 FETCH (RFC822.TEXT "") + * 1 FETCH (RFC822.SIZE 0) + * 1 FETCH (BODY ("TEXT" "PLAIN" NIL NIL NIL "7BIT" 0 0) + * 1 FETCH (BODYSTRUCTURE ("TEXT" "PLAIN" NIL NIL NIL "7BIT" 0 0) + * 1 FETCH (BODY[<section>] "") + * 1 FETCH (BODY[<section>]<partial> "") + + In some cases, a client may not be able to distinguish between "NIL + FETCH responses" received because a message was expunged and those + received because the data actually was NIL. For example, a * 5 + FETCH (FLAGS ()) response could be received if no flags were set on + message 5, or because message 5 was expunged. In a case of potential + ambiguity, the client SHOULD issue a command such as NOOP to force + the sending of the EXPUNGE responses to resolve any ambiguity. + + Example: (Building upon the scenario outlined in 4.1.) + + <Client #2 attempts to access a mix of expunged and non-expunged + messages. Normal data is returned for non-expunged message, "NIL + FETCH responses" are returned for expunged messages> + + + + + + + + +Gahrns Informational [Page 8] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + + C2: B002 FETCH 3:5 ENVELOPE + S2: * 3 FETCH ENVELOPE . . . (ENVELOPE info returned) + S2: * 4 FETCH ENVELOPE (NIL NIL NIL NIL NIL NIL NIL NIL + NIL NIL) + S2: * 5 FETCH ENVELOPE (NIL NIL NIL NIL NIL NIL NIL NIL + NIL NIL) + S2: B002 OK FETCH Completed + + <Client #2 attempts to FETCH only expunged messages and receives a + tagged NO response> + + C2: B002 FETCH 4:7 ENVELOPE + S2: B002 NO Messages 4:7 have been expunged. + + +4.1.4 To avoid the situation altogether, the server MAY fail the + EXPUNGE of a multi-accessed mailbox + + In some cases, this behavior may not be practical. For example, if a + large number of clients are accessing a shared mailbox, the window in + which no clients have the mailbox accessed may be small or non- + existent, effectively rendering the message unexpungeable. + + +4.2. Storing of expunged messages + + Following are some strategies an IMAP server may choose to use when + dealing with a STORE command on expunged messages. + + +4.2.1 If the ".SILENT" suffix is used, and the STORE completed + successfully for all the non-expunged messages, the server SHOULD + return a tagged OK. + + Example: (Building upon the scenario outlined in 4.1.) + + <Client #2 tries to silently STORE flags on expunged and non- + expunged messages. The server sets the flags on the non-expunged + messages and returns OK> + + C2: B001 STORE 1:7 +FLAGS.SILENT (\SEEN) + S2: B001 OK + + + + + + + + + +Gahrns Informational [Page 9] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + +4.2.2. If the ".SILENT" suffix is not used, and only expunged messages + are referenced, the server SHOULD return only a tagged NO. + + Example: (Building upon the scenario outlined in 4.1.) + + <Client #2 tries to STORE flags only on expunged messages> + + C2: B001 STORE 5:7 +FLAGS (\SEEN) + S2: B001 NO Messages have been expunged + + +4.2.3. If the ".SILENT" suffix is not used, and a mixture of expunged + and non-expunged messages are referenced, the server MAY set the + flags and return a FETCH response for the non-expunged messages + along with a tagged NO. + + After receiving a tagged NO STORE response, the client SHOULD issue a + NOOP command so that it will be informed of any pending EXPUNGE + responses. The client may then either reissue the failed STORE + command, or by examining the EXPUNGE responses from the NOOP and + FETCH responses from the STORE, determine that the STORE failed + because of pending expunges. + + Example: (Building upon the scenario outlined in 4.1.) + + <Client #2 tries to STORE flags on a mixture of expunged and non- + expunged messages> + + C2: B001 STORE 1:7 +FLAGS (\SEEN) + S2: * FETCH 1 FLAGS (\SEEN) + S2: * FETCH 2 FLAGS (\SEEN) + S2: * FETCH 3 FLAGS (\SEEN) + S2: B001 NO Some of the messages no longer exist. + + C2: B002 NOOP + S2: * 4 EXPUNGE + S2: * 4 EXPUNGE + S2: * 4 EXPUNGE + S2: * 4 EXPUNGE + S2: * 3 EXISTS + S2: B002 OK NOOP Completed. + + <By receiving FETCH responses for messages 1:3, and an EXPUNGE + response that indicates messages 4:7 have been expunged, the client + does not need to re-issue the STORE> + + + + + + +Gahrns Informational [Page 10] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + +4.2.4. If the ".SILENT" suffix is not used, and a mixture of expunged + and non-expunged messages are referenced, the server MAY return + an untagged NO and not set any flags. + + After receiving a tagged NO STORE response, the client SHOULD issue a + NOOP command so that it will be informed of any pending EXPUNGE + responses. The client would then re-issue the STORE command after + updating its message list per any EXPUNGE response. + + If a large number of clients are accessing a shared mailbox, the + window in which there are no pending expunges may be small or non- + existent, effectively disallowing a client from setting the flags on + all messages at once. + + Example: (Building upon the scenario outlined in 4.1.) + + <Client #2 tries to STORE flags on a mixture of expunged and non- + expunged messages> + + C2: B001 STORE 1:7 +FLAGS (\SEEN) + S2: B001 NO Some of the messages no longer exist. + + <Client #2 issues a NOOP to be informed of the EXPUNGED messages> + + C2: B002 NOOP + S2: * 4 EXPUNGE + S2: * 4 EXPUNGE + S2: * 4 EXPUNGE + S2: * 4 EXPUNGE + S2: * 3 EXISTS + S2: B002 OK NOOP Completed. + + <Client #2 updates its message list and re-issues the STORE on only + those messages that have not been expunged> + + C2: B003 STORE 1:3 +FLAGS (\SEEN) S2: * FETCH 1 FLAGS + (\SEEN) S2: * FETCH 2 FLAGS (\SEEN) S2: * FETCH 3 FLAGS + (\SEEN) S2: B003 OK STORE Completed + + +4.3. Searching of expunged messages + + A server MAY simply not return a search response for messages that + have been expunged and it has not been able to inform the client + about. If a client was expecting a particular message to be returned + in a search result, and it was not, the client SHOULD issue a NOOP + command to see if the message was expunged by another client. + + + + +Gahrns Informational [Page 11] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + +4.4 Copying of expunged messages + + COPY is the only IMAP4 sequence number command that is safe to allow + an EXPUNGE response on. This is because a client is not permitted to + cascade several COPY commands together. A client is required to wait + and confirm that the copy worked before issuing another one. + +4.4.1 The server MAY disallow the COPY of messages in a multi-access + mailbox that contains expunged messages. + + Pending EXPUNGE response(s) MUST be returned to the COPY command. + + Example: + + C: A001 COPY 2,4,6,8 FRED + S: * 4 EXPUNGE + S: A001 NO COPY rejected, because some of the requested + messages were expunged + + Note: Non of the above messages are copied because if a COPY command + is unsuccessful, the server MUST restore the destination mailbox to + its state before the COPY attempt. + + +4.4.2 The server MAY allow the COPY of messages in a multi-access + mailbox that contains expunged messages. + + Pending EXPUNGE response(s) MUST be returned to the COPY command. + Messages that are copied are messages corresponding to sequence + numbers before any EXPUNGE response. + + Example: + + C: A001 COPY 2,4,6,8 FRED + S: * 3 EXPUNGE + S: A001 OK COPY completed + + In the above example, the messages that are copied to FRED are + messages 2,4,6,8 at the start of the COPY command. These are + equivalent to messages 2,3,5,7 at the end of the COPY command. The + EXPUNGE response can't take place until after the messages from the + COPY command are identified (because of the "no expunge while no + commands in progress" rule). + + + + + + + + +Gahrns Informational [Page 12] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + + Example: + + C: A001 COPY 2,4,6,8 FRED + S: * 4 EXPUNGE + S: A001 OK COPY completed + + In the above example, message 4 was copied before it was expunged, + and MUST appear in the destination mailbox FRED. + + +5. Security Considerations + + This document describes behavior of servers that use the IMAP4 + protocol, and as such, has the same security considerations as + described in [RFC-2060]. + + In particular, some described server behavior does not allow for the + immediate deletion of information when a mailbox is accessed by + multiple clients. This may be a consideration when dealing with + sensitive information where immediate deletion would be preferred. + + +6. References + + [RFC-2060], Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 2060, University of Washington, December 1996. + + [RFC-2119], Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", RFC 2119, Harvard University, March 1997. + + +7. Acknowledgments + + This document is the result of discussions on the IMAP4 mailing list + and is meant to reflect consensus of this group. In particular, + Raymond Cheng, Mark Crispin, Jim Evans, Erik Forsberg, Steve Hole, + Mark Keasling, Barry Leiba, Syd Logan, John Mani, Pat Moran, Larry + Osterman, Chris Newman, Bart Schaefer, Vladimir Vulovic, and Jack De + Winter were active participants in this discussion or made + suggestions to this document. + + + + + + + + + + + +Gahrns Informational [Page 13] + +RFC 2180 IMAP4 Multi-Accessed Mailbox Practice July 1997 + + +8. Author's Address + + Mike Gahrns + Microsoft + One Microsoft Way + Redmond, WA, 98072 + + Phone: (206) 936-9833 + EMail: mikega@microsoft.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Gahrns Informational [Page 14] + diff --git a/imap/docs/rfc/rfc2193.txt b/imap/docs/rfc/rfc2193.txt new file mode 100644 index 00000000..2fec58d7 --- /dev/null +++ b/imap/docs/rfc/rfc2193.txt @@ -0,0 +1,507 @@ + + + + + + +Network Working Group M. Gahrns +Request for Comments: 2193 Microsoft +Category: Standards Track September 1997 + + + IMAP4 Mailbox Referrals + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +1. Abstract + + When dealing with large amounts of users, messages and geographically + dispersed IMAP4 [RFC-2060] servers, it is often desirable to + distribute messages amongst different servers within an organization. + For example an administrator may choose to store user's personal + mailboxes on a local IMAP4 server, while storing shared mailboxes + remotely on another server. This type of configuration is common + when it is uneconomical to store all data centrally due to limited + bandwidth or disk resources. + + Mailbox referrals allow clients to seamlessly access mailboxes that + are distributed across several IMAP4 servers. + + A referral mechanism can provide efficiencies over the alternative + "proxy method", in which the local IMAP4 server contacts the remote + server on behalf of the client, and then transfers the data from the + remote server to itself, and then on to the client. The referral + mechanism's direct client connection to the remote server is often a + more efficient use of bandwidth, and does not require the local + server to impersonate the client when authenticating to the remote + server. + +2. Conventions used in this document + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. + + A home server, is an IMAP4 server that contains the user's inbox. + + A remote mailbox is a mailbox that is not hosted on the user's home + server. + + + + +Gahrns Standards Track [Page 1] + +RFC 2193 IMAP4 Mailbox Referrals September 1997 + + + A remote server is a server that contains remote mailboxes. + + A shared mailbox, is a mailbox that multiple users have access to. + + An IMAP mailbox referral is when the server directs the client to + another IMAP mailbox. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC-2119]. + +3. Introduction and Overview + + IMAP4 servers that support this extension MUST list the keyword + MAILBOX-REFERRALS in their CAPABILITY response. No client action is + needed to invoke the MAILBOX-REFERRALS capability in a server. + + A MAILBOX-REFERRALS capable IMAP4 server MUST NOT return referrals + that result in a referrals loop. + + A referral response consists of a tagged NO response and a REFERRAL + response code. The REFERRAL response code MUST contain as an + argument a one or more valid URLs separated by a space as defined in + [RFC-1738]. If a server replies with multiple URLs for a particular + object, they MUST all be of the same type. In this case, the URL MUST + be an IMAP URL as defined in [RFC-2192]. A client that supports the + REFERRALS extension MUST be prepared for a URL of any type, but it + need only be able to process IMAP URLs. + + A server MAY respond with multiple IMAP mailbox referrals if there is + more than one replica of the mailbox. This allows the implementation + of a load balancing or failover scheme. How a server keeps multiple + replicas of a mailbox in sync is not addressed by this document. + + If the server has a preferred order in which the client should + attempt to access the URLs, the preferred URL SHOULD be listed in the + first, with the remaining URLs presented in descending order of + preference. If multiple referrals are given for a mailbox, a server + should be aware that there are synchronization issues for a client if + the UIDVALIDITY of the referred mailboxes are different. + + An IMAP mailbox referral may be given in response to an IMAP command + that specifies a mailbox as an argument. + + + + + + + + +Gahrns Standards Track [Page 2] + +RFC 2193 IMAP4 Mailbox Referrals September 1997 + + + Example: + + A001 NO [REFERRAL IMAP://user;AUTH=*@SERVER2/REMOTE]Remote Mailbox + + NOTE: user;AUTH=* is specified as required by [RFC-2192] to avoid a + client falling back to anonymous login. + + Remote mailboxes and their inferiors, that are accessible only via + referrals SHOULD NOT appear in LIST and LSUB responses issued against + the user's home server. They MUST appear in RLIST and RLSUB + responses issued against the user's home server. Hierarchy referrals, + in which a client would be required to connect to the remote server + to issue a LIST to discover the inferiors of a mailbox are not + addressed in this document. + + For example, if shared mailboxes were only accessible via referrals + on a remote server, a RLIST "" "#SHARED/%" command would return the + same response if issued against the user's home server or the remote + server. + + Note: Mailboxes that are available on the user's home server do not + need to be available on the remote server. In addition, there may be + additional mailboxes available on the remote server, but they will + not accessible to the client via referrals unless they appear in the + LIST response to the RLIST command against the user's home server. + + A MAILBOX-REFERRALS capable client will issue the RLIST and RLSUB + commands in lieu of LIST and LSUB. The RLIST and RLSUB commands + behave identically to their LIST and LSUB counterparts, except remote + mailboxes are returned in addition to local mailboxes in the LIST and + LSUB responses. This avoids displaying to a non MAILBOX-REFERRALS + enabled client inaccessible remote mailboxes. + +4.1. SELECT, EXAMINE, DELETE, SUBSCRIBE, UNSUBSCRIBE, STATUS and APPEND + Referrals + + An IMAP4 server MAY respond to the SELECT, EXAMINE, DELETE, + SUBSCRIBE, UNSUBSCRIBE, STATUS or APPEND command with one or more + IMAP mailbox referrals to indicate to the client that the mailbox is + hosted on a remote server. + + When a client processes an IMAP mailbox referral, it will open a new + connection or use an existing connection to the remote server so that + it is able to issue the commands necessary to process the remote + mailbox. + + + + + + +Gahrns Standards Track [Page 3] + +RFC 2193 IMAP4 Mailbox Referrals September 1997 + + + Example: <IMAP4 connection to home server> + + C: A001 DELETE "SHARED/FOO" + S: A001 NO [REFERRAL IMAP://user;AUTH=*@SERVER2/SHARED/FOO] + Remote mailbox. Try SERVER2. + + <Client established a second connection to SERVER2 and + issues the DELETE command on the referred mailbox> + + S: * OK IMAP4rev1 server ready + C: B001 AUTHENTICATE KERBEROS_V4 + <authentication exchange> + S: B001 OK user is authenticated + + C: B002 DELETE "SHARED/FOO" + S: B002 OK DELETE completed + + Example: <IMAP4 connection to home server> + + C: A001 SELECT REMOTE + S: A001 NO [REFERRAL IMAP://user;AUTH=*@SERVER2/REMOTE + IMAP://user;AUTH=*@SERVER3/REMOTE] Remote mailbox. + Try SERVER2 or SERVER3. + + <Client opens second connection to remote server, and + issues the commands needed to process the items in the + remote mailbox> + + S: * OK IMAP4rev1 server ready + C: B001 AUTHENTICATE KERBEROS_V4 + <authentication exchange> + S: B001 OK user is authenticated + + C: B002 SELECT REMOTE + S: * 12 EXISTS + S: * 1 RECENT + S: * OK [UNSEEN 10] Message 10 is first unseen + S: * OK [UIDVALIDITY 123456789] + S: * FLAGS (Answered Flagged Deleted Seen Draft) + S: * OK [PERMANENTFLAGS (Answered Deleted Seen ] + S: B002 OK [READ-WRITE] Selected completed + + C: B003 FETCH 10:12 RFC822 + S: * 10 FETCH . . . + S: * 11 FETCH . . . + S: * 12 FETCH . . . + S: B003 OK FETCH Completed + + + + +Gahrns Standards Track [Page 4] + +RFC 2193 IMAP4 Mailbox Referrals September 1997 + + + <Client is finished processing the REMOTE mailbox and + wants to process a mailbox on its home server> + + C: B004 LOGOUT + S: * BYE IMAP4rev1 server logging out + S: B004 OK LOGOUT Completed + + <Client continues with first connection> + + C: A002 SELECT INBOX + S: * 16 EXISTS + S: * 2 RECENT + S: * OK [UNSEEN 10] Message 10 is first unseen + S: * OK [UIDVALIDITY 123456789] + S: * FLAGS (Answered Flagged Deleted Seen Draft) + S: * OK [PERMANENTFLAGS (Answered Deleted Seen ] + S: A002 OK [READ-WRITE] Selected completed + +4.2. CREATE Referrals + + An IMAP4 server MAY respond to the CREATE command with one or more + IMAP mailbox referrals, if it wishes to direct the client to issue + the CREATE against another server. The server can employ any means, + such as examining the hierarchy of the specified mailbox name, in + determining which server the mailbox should be created on. + + Example: + + C: A001 CREATE "SHARED/FOO" + S: A001 NO [REFERRAL IMAP://user;AUTH=*@SERVER2/SHARED/FOO] + Mailbox should be created on remote server + + Alternatively, because a home server is required to maintain a + listing of referred remote mailboxes, a server MAY allow the creation + of a mailbox that will ultimately reside on a remote server against + the home server, and provide referrals on subsequent commands that + manipulate the mailbox. + + Example: + + C: A001 CREATE "SHARED/FOO" + S: A001 OK CREATE succeeded + + C: A002 SELECT "SHARED/FOO" + S: A002 NO [REFERRAL IMAP://user;AUTH=*@SERVER2/SHARED/FOO] + Remote mailbox. Try SERVER2 + + + + + +Gahrns Standards Track [Page 5] + +RFC 2193 IMAP4 Mailbox Referrals September 1997 + + +4.3. RENAME Referrals + + An IMAP4 server MAY respond to the RENAME command with one or more + pairs of IMAP mailbox referrals. In each pair of IMAP mailbox + referrals, the first one is an URL to the existing mailbox name and + the second is an URL to the requested new mailbox name. + + If within an IMAP mailbox referral pair, the existing and new mailbox + URLs are on different servers, the remote servers are unable to + perform the RENAME operation. To achieve the same behavior of + server RENAME, the client MAY issue the constituent CREATE, FETCH, + APPEND, and DELETE commands against both servers. + + If within an IMAP mailbox referral pair, the existing and new mailbox + URLs are on the same server it is an indication that the currently + connected server is unable to perform the operation. The client can + simply re-issue the RENAME command on the remote server. + + Example: + + C: A001 RENAME FOO BAR + S: A001 NO [REFERRAL IMAP://user;AUTH=*@SERVER1/FOO + IMAP://user;AUTH=*@SERVER2/BAR] Unable to rename mailbox + across servers + + Since the existing and new mailbox names are on different servers, + the client would be required to make a connection to both servers and + issue the constituent commands require to achieve the RENAME. + + Example: + + C: A001 RENAME FOO BAR + S: A001 NO [REFERRAL IMAP://user;AUTH=*@SERVER2/FOO + IMAP://user;AUTH=*@SERVER2/BAR] Unable to rename mailbox + located on SERVER2 + + Since both the existing and new mailbox are on the same remote + server, the client can simply make a connection to the remote server + and re-issue the RENAME command. + +4.4. COPY Referrals + + An IMAP4 server MAY respond to the COPY command with one or more IMAP + mailbox referrals. This indicates that the destination mailbox is on + a remote server. To achieve the same behavior of a server COPY, the + client MAY issue the constituent FETCH and APPEND commands against + both servers. + + + + +Gahrns Standards Track [Page 6] + +RFC 2193 IMAP4 Mailbox Referrals September 1997 + + + Example: + + C: A001 COPY 1 "SHARED/STUFF" + S: A001 NO [REFERRAL IMAP://user;AUTH=*@SERVER2/SHARED/STUFF] + Unable to copy message(s) to SERVER2. + +5.1 RLIST command + + Arguments: reference name + mailbox name with possible wildcards + + Responses: untagged responses: LIST + + Result: OK - RLIST Completed + NO - RLIST Failure + BAD - command unknown or arguments invalid + + The RLIST command behaves identically to its LIST counterpart, except + remote mailboxes are returned in addition to local mailboxes in the + LIST responses. + +5.2 RLSUB Command + + Arguments: reference name + mailbox name with possible wildcards + + Responses: untagged responses: LSUB + + Result: OK - RLSUB Completed + NO - RLSUB Failure + BAD - command unknown or arguments invalid + + The RLSUB command behaves identically to its LSUB counterpart, except + remote mailboxes are returned in addition to local mailboxes in the + LSUB responses. + +6. Formal Syntax + + The following syntax specification uses the augmented Backus-Naur + Form (BNF) as described in [ABNF]. + + list_mailbox = <list_mailbox> as defined in [RFC-2060] + + mailbox = <mailbox> as defined in [RFC-2060] + + mailbox_referral = <tag> SPACE "NO" SPACE + <referral_response_code> (text / text_mime2) + ; See [RFC-2060] for <tag>, text and text_mime2 definition + + + +Gahrns Standards Track [Page 7] + +RFC 2193 IMAP4 Mailbox Referrals September 1997 + + + referral_response_code = "[" "REFERRAL" 1*(SPACE <url>) "]" + ; See [RFC-1738] for <url> definition + + rlist = "RLIST" SPACE mailbox SPACE list_mailbox + + rlsub = "RLSUB" SPACE mailbox SPACE list_mailbox + +6. Security Considerations + + The IMAP4 referral mechanism makes use of IMAP URLs, and as such, + have the same security considerations as general internet URLs [RFC- + 1738], and in particular IMAP URLs [RFC-2192]. + + With the MAILBOX-REFERRALS capability, it is potentially easier to + write a rogue server that injects a bogus referral response that + directs a user to an incorrect mailbox. Although referrals reduce + the effort to write such a server, the referral response makes + detection of the intrusion easier. + +7. References + + [RFC-2060], Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 2060, University of Washington, December 1996. + + [RFC-2192], Newman, C., "IMAP URL Scheme", RFC 2192, Innosoft, + September 1997. + + [RFC-1738], Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform + Resource Locators (URL)", RFC 1738, CERN, Xerox Corporation, + University of Minnesota, December 1994. + + [RFC-2119], Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", RFC 2119, Harvard University, March 1997. + + [ABNF], DRUMS working group, Dave Crocker Editor, "Augmented BNF for + Syntax Specifications: ABNF", Work in Progress, Internet Mail + Consortium, April 1997. + +8. Acknowledgments + + Many valuable suggestions were received from private discussions and + the IMAP4 mailing list. In particular, Raymond Cheng, Mark Crispin, + Mark Keasling, Chris Newman and Larry Osterman made significant + contributions to this document. + + + + + + + +Gahrns Standards Track [Page 8] + +RFC 2193 IMAP4 Mailbox Referrals September 1997 + + +9. Author's Address + + Mike Gahrns + Microsoft + One Microsoft Way + Redmond, WA, 98072 + + Phone: (206) 936-9833 + EMail: mikega@microsoft.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Gahrns Standards Track [Page 9] + diff --git a/imap/docs/rfc/rfc2195.txt b/imap/docs/rfc/rfc2195.txt new file mode 100644 index 00000000..4a2725bf --- /dev/null +++ b/imap/docs/rfc/rfc2195.txt @@ -0,0 +1,283 @@ + + + + + + +Network Working Group J. Klensin +Request for Comments: 2195 R. Catoe +Category: Standards Track P. Krumviede +Obsoletes: 2095 MCI + September 1997 + + + IMAP/POP AUTHorize Extension for Simple Challenge/Response + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + While IMAP4 supports a number of strong authentication mechanisms as + described in RFC 1731, it lacks any mechanism that neither passes + cleartext, reusable passwords across the network nor requires either + a significant security infrastructure or that the mail server update + a mail-system-wide user authentication file on each mail access. + This specification provides a simple challenge-response + authentication protocol that is suitable for use with IMAP4. Since + it utilizes Keyed-MD5 digests and does not require that the secret be + stored in the clear on the server, it may also constitute an + improvement on APOP for POP3 use as specified in RFC 1734. + +1. Introduction + + Existing Proposed Standards specify an AUTHENTICATE mechanism for the + IMAP4 protocol [IMAP, IMAP-AUTH] and a parallel AUTH mechanism for + the POP3 protocol [POP3-AUTH]. The AUTHENTICATE mechanism is + intended to be extensible; the four methods specified in [IMAP-AUTH] + are all fairly powerful and require some security infrastructure to + support. The base POP3 specification [POP3] also contains a + lightweight challenge-response mechanism called APOP. APOP is + associated with most of the risks associated with such protocols: in + particular, it requires that both the client and server machines have + access to the shared secret in cleartext form. CRAM offers a method + for avoiding such cleartext storage while retaining the algorithmic + simplicity of APOP in using only MD5, though in a "keyed" method. + + + + + + + +Klensin, Catoe & Krumviede Standards Track [Page 1] + +RFC 2195 IMAP/POP AUTHorize Extension September 1997 + + + At present, IMAP [IMAP] lacks any facility corresponding to APOP. + The only alternative to the strong mechanisms identified in [IMAP- + AUTH] is a presumably cleartext username and password, supported + through the LOGIN command in [IMAP]. This document describes a + simple challenge-response mechanism, similar to APOP and PPP CHAP + [PPP], that can be used with IMAP (and, in principle, with POP3). + + This mechanism also has the advantage over some possible alternatives + of not requiring that the server maintain information about email + "logins" on a per-login basis. While mechanisms that do require such + per-login history records may offer enhanced security, protocols such + as IMAP, which may have several connections between a given client + and server open more or less simultaneous, may make their + implementation particularly challenging. + +2. Challenge-Response Authentication Mechanism (CRAM) + + The authentication type associated with CRAM is "CRAM-MD5". + + The data encoded in the first ready response contains an + presumptively arbitrary string of random digits, a timestamp, and the + fully-qualified primary host name of the server. The syntax of the + unencoded form must correspond to that of an RFC 822 'msg-id' + [RFC822] as described in [POP3]. + + The client makes note of the data and then responds with a string + consisting of the user name, a space, and a 'digest'. The latter is + computed by applying the keyed MD5 algorithm from [KEYED-MD5] where + the key is a shared secret and the digested text is the timestamp + (including angle-brackets). + + This shared secret is a string known only to the client and server. + The `digest' parameter itself is a 16-octet value which is sent in + hexadecimal format, using lower-case ASCII characters. + + When the server receives this client response, it verifies the digest + provided. If the digest is correct, the server should consider the + client authenticated and respond appropriately. + + Keyed MD5 is chosen for this application because of the greater + security imparted to authentication of short messages. In addition, + the use of the techniques described in [KEYED-MD5] for precomputation + of intermediate results make it possible to avoid explicit cleartext + storage of the shared secret on the server system by instead storing + the intermediate results which are known as "contexts". + + + + + + +Klensin, Catoe & Krumviede Standards Track [Page 2] + +RFC 2195 IMAP/POP AUTHorize Extension September 1997 + + + CRAM does not support a protection mechanism. + + Example: + + The examples in this document show the use of the CRAM mechanism with + the IMAP4 AUTHENTICATE command [IMAP-AUTH]. The base64 encoding of + the challenges and responses is part of the IMAP4 AUTHENTICATE + command, not part of the CRAM specification itself. + + S: * OK IMAP4 Server + C: A0001 AUTHENTICATE CRAM-MD5 + S: + PDE4OTYuNjk3MTcwOTUyQHBvc3RvZmZpY2UucmVzdG9uLm1jaS5uZXQ+ + C: dGltIGI5MTNhNjAyYzdlZGE3YTQ5NWI0ZTZlNzMzNGQzODkw + S: A0001 OK CRAM authentication successful + + In this example, the shared secret is the string + 'tanstaaftanstaaf'. Hence, the Keyed MD5 digest is produced by + calculating + + MD5((tanstaaftanstaaf XOR opad), + MD5((tanstaaftanstaaf XOR ipad), + <1896.697170952@postoffice.reston.mci.net>)) + + where ipad and opad are as defined in the keyed-MD5 Work in + Progress [KEYED-MD5] and the string shown in the challenge is the + base64 encoding of <1896.697170952@postoffice.reston.mci.net>. The + shared secret is null-padded to a length of 64 bytes. If the + shared secret is longer than 64 bytes, the MD5 digest of the + shared secret is used as a 16 byte input to the keyed MD5 + calculation. + + This produces a digest value (in hexadecimal) of + + b913a602c7eda7a495b4e6e7334d3890 + + The user name is then prepended to it, forming + + tim b913a602c7eda7a495b4e6e7334d3890 + + Which is then base64 encoded to meet the requirements of the IMAP4 + AUTHENTICATE command (or the similar POP3 AUTH command), yielding + + dGltIGI5MTNhNjAyYzdlZGE3YTQ5NWI0ZTZlNzMzNGQzODkw + + + + + + + + +Klensin, Catoe & Krumviede Standards Track [Page 3] + +RFC 2195 IMAP/POP AUTHorize Extension September 1997 + + +3. References + + [CHAP] Lloyd, B., and W. Simpson, "PPP Authentication Protocols", + RFC 1334, October 1992. + + [IMAP] Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 2060, University of Washington, December 1996. + + [IMAP-AUTH] Myers, J., "IMAP4 Authentication Mechanisms", + RFC 1731, Carnegie Mellon, December 1994. + + [KEYED-MD5] Krawczyk, Bellare, Canetti, "HMAC: Keyed-Hashing for + Message Authentication", RFC 2104, February 1997. + + [MD5] Rivest, R., "The MD5 Message Digest Algorithm", + RFC 1321, MIT Laboratory for Computer Science, April 1992. + + [POP3] Myers, J., and M. Rose, "Post Office Protocol - Version 3", + STD 53, RFC 1939, Carnegie Mellon, May 1996. + + [POP3-AUTH] Myers, J., "POP3 AUTHentication command", RFC 1734, + Carnegie Mellon, December, 1994. + +4. Security Considerations + + It is conjectured that use of the CRAM authentication mechanism + provides origin identification and replay protection for a session. + Accordingly, a server that implements both a cleartext password + command and this authentication type should not allow both methods of + access for a given user. + + While the saving, on the server, of "contexts" (see section 2) is + marginally better than saving the shared secrets in cleartext as is + required by CHAP [CHAP] and APOP [POP3], it is not sufficient to + protect the secrets if the server itself is compromised. + Consequently, servers that store the secrets or contexts must both be + protected to a level appropriate to the potential information value + in user mailboxes and identities. + + As the length of the shared secret increases, so does the difficulty + of deriving it. + + While there are now suggestions in the literature that the use of MD5 + and keyed MD5 in authentication procedures probably has a limited + effective lifetime, the technique is now widely deployed and widely + understood. It is believed that this general understanding may + assist with the rapid replacement, by CRAM-MD5, of the current uses + of permanent cleartext passwords in IMAP. This document has been + + + +Klensin, Catoe & Krumviede Standards Track [Page 4] + +RFC 2195 IMAP/POP AUTHorize Extension September 1997 + + + deliberately written to permit easy upgrading to use SHA (or whatever + alternatives emerge) when they are considered to be widely available + and adequately safe. + + Even with the use of CRAM, users are still vulnerable to active + attacks. An example of an increasingly common active attack is 'TCP + Session Hijacking' as described in CERT Advisory CA-95:01 [CERT95]. + + See section 1 above for additional discussion. + +5. Acknowledgements + + This memo borrows ideas and some text liberally from [POP3] and + [RFC-1731] and thanks are due the authors of those documents. Ran + Atkinson made a number of valuable technical and editorial + contributions to the document. + +6. Authors' Addresses + + John C. Klensin + MCI Telecommunications + 800 Boylston St, 7th floor + Boston, MA 02199 + USA + + EMail: klensin@mci.net + Phone: +1 617 960 1011 + + Randy Catoe + MCI Telecommunications + 2100 Reston Parkway + Reston, VA 22091 + USA + + EMail: randy@mci.net + Phone: +1 703 715 7366 + + Paul Krumviede + MCI Telecommunications + 2100 Reston Parkway + Reston, VA 22091 + USA + + EMail: paul@mci.net + Phone: +1 703 715 7251 + + + + + + +Klensin, Catoe & Krumviede Standards Track [Page 5] + diff --git a/imap/docs/rfc/rfc2221.txt b/imap/docs/rfc/rfc2221.txt new file mode 100644 index 00000000..81d00620 --- /dev/null +++ b/imap/docs/rfc/rfc2221.txt @@ -0,0 +1,283 @@ + + + + + + +Network Working Group M. Gahrns +Request for Comments: 2221 Microsoft +Category: Standards Track October 1997 + + + IMAP4 Login Referrals + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (1997). All Rights Reserved. + +1. Abstract + + When dealing with large amounts of users and many IMAP4 [RFC-2060] + servers, it is often necessary to move users from one IMAP4 server to + another. For example, hardware failures or organizational changes + may dictate such a move. + + Login referrals allow clients to transparently connect to an + alternate IMAP4 server, if their home IMAP4 server has changed. + + A referral mechanism can provide efficiencies over the alternative + 'proxy method', in which the local IMAP4 server contacts the remote + server on behalf of the client, and then transfers the data from the + remote server to itself, and then on to the client. The referral + mechanism's direct client connection to the remote server is often a + more efficient use of bandwidth, and does not require the local + server to impersonate the client when authenticating to the remote + server. + +2. Conventions used in this document + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. + + A home server, is an IMAP4 server that contains the user's inbox. + + A remote server is a server that contains remote mailboxes. + + + + + +Gahrns Standards Track [Page 1] + +RFC 2221 IMAP4 Login Referrals October 1997 + + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC-2119]. + +3. Introduction and Overview + + IMAP4 servers that support this extension MUST list the keyword + LOGIN-REFERRALS in their CAPABILITY response. No client action is + needed to invoke the LOGIN-REFERRALS capability in a server. + + A LOGIN-REFERRALS capable IMAP4 server SHOULD NOT return a referral + to a server that will return a referral. A client MUST NOT follow + more than 10 levels of referral without consulting the user. + + A LOGIN-REFERRALS response code MUST contain as an argument a valid + IMAP server URL as defined in [IMAP-URL]. + + A home server referral consists of either a tagged NO or OK, or an + untagged BYE response that contains a LOGIN-REFERRALS response code. + + Example: A001 NO [REFERRAL IMAP://user;AUTH=*@SERVER2/] Remote Server + + NOTE: user;AUTH=* is specified as required by [IMAP-URL] to avoid a + client falling back to anonymous login. + +4. Home Server Referrals + + A home server referral may be returned in response to an AUTHENTICATE + or LOGIN command, or it may appear in the connection startup banner. + If a server returns a home server referral in a tagged NO response, + that server does not contain any mailboxes that are accessible to the + user. If a server returns a home server referral in a tagged OK + response, it indicates that the user's personal mailboxes are + elsewhere, but the server contains public mailboxes which are + readable by the user. After receiving a home server referral, the + client can not make any assumptions as to whether this was a + permanent or temporary move of the user. + +4.1. LOGIN and AUTHENTICATE Referrals + + An IMAP4 server MAY respond to a LOGIN or AUTHENTICATE command with a + home server referral if it wishes to direct the user to another IMAP4 + server. + + Example: C: A001 LOGIN MIKE PASSWORD + S: A001 NO [REFERRAL IMAP://MIKE@SERVER2/] Specified user + is invalid on this server. Try SERVER2. + + + + +Gahrns Standards Track [Page 2] + +RFC 2221 IMAP4 Login Referrals October 1997 + + + Example: C: A001 LOGIN MATTHEW PASSWORD + S: A001 OK [REFERRAL IMAP://MATTHEW@SERVER2/] Specified + user's personal mailboxes located on Server2, but + public mailboxes are available. + + Example: C: A001 AUTHENTICATE GSSAPI + <authentication exchange> + S: A001 NO [REFERRAL IMAP://user;AUTH=GSSAPI@SERVER2/] + Specified user is invalid on this server. Try + SERVER2. + +4.2. BYE at connection startup referral + + An IMAP4 server MAY respond with an untagged BYE and a REFERRAL + response code that contains an IMAP URL to a home server if it is not + willing to accept connections and wishes to direct the client to + another IMAP4 server. + + Example: S: * BYE [REFERRAL IMAP://user;AUTH=*@SERVER2/] Server not + accepting connections. Try SERVER2 + +5. Formal Syntax + + The following syntax specification uses the augmented Backus-Naur + Form (BNF) as described in [ABNF]. + + This amends the "resp_text_code" element of the IMAP4 grammar + described in [RFC-2060] + + resp_text_code =/ "REFERRAL" SPACE <imapurl> + ; See [IMAP-URL] for definition of <imapurl> + ; See [RFC-2060] for base definition of resp_text_code + +6. Security Considerations + + The IMAP4 login referral mechanism makes use of IMAP URLs, and as + such, have the same security considerations as general internet URLs + [RFC-1738], and in particular IMAP URLs [IMAP-URL]. + + A server MUST NOT give a login referral if authentication for that + user fails. This is to avoid revealing information about the user's + account to an unauthorized user. + + With the LOGIN-REFERRALS capability, it is potentially easier to + write a rogue 'password catching' server that collects login data and + then refers the client to their actual IMAP4 server. Although + referrals reduce the effort to write such a server, the referral + response makes detection of the intrusion easier. + + + +Gahrns Standards Track [Page 3] + +RFC 2221 IMAP4 Login Referrals October 1997 + + +7. References + + [RFC-2060], Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 2060, December 1996. + + [IMAP-URL], Newman, C., "IMAP URL Scheme", RFC 2192, Innosoft, + September 1997. + + [RFC-1738], Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform + Resource Locators (URL)", RFC 1738, December 1994. + + [RFC-2119], Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", RFC 2119, March 1997. + + [ABNF], DRUMS working group, Dave Crocker Editor, "Augmented BNF for + Syntax Specifications: ABNF", Work in Progress. + +8. Acknowledgments + + Many valuable suggestions were received from private discussions and + the IMAP4 mailing list. In particular, Raymond Cheng, Mark Crispin, + Mark Keasling Chris Newman and Larry Osterman made significant + contributions to this document. + +9. Author's Address + + Mike Gahrns + Microsoft + One Microsoft Way + Redmond, WA, 98072 + + Phone: (206) 936-9833 + EMail: mikega@microsoft.com + + + + + + + + + + + + + + + + + + +Gahrns Standards Track [Page 4] + +RFC 2221 IMAP4 Login Referrals October 1997 + + +10. Full Copyright Statement + + Copyright (C) The Internet Society (1997). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implmentation may be prepared, copied, published + andand distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. + + This document and the information contained herein is provided on an + "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING + TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING + BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION + HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF + MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." + + + + + + + + + + + + + + + + + + + + + + + + +Gahrns Standards Track [Page 5] + diff --git a/imap/docs/rfc/rfc2342.txt b/imap/docs/rfc/rfc2342.txt new file mode 100644 index 00000000..0926646d --- /dev/null +++ b/imap/docs/rfc/rfc2342.txt @@ -0,0 +1,563 @@ + + + + + + +Network Working Group M. Gahrns +Request for Comments: 2342 Microsoft +Category: Standards Track C. Newman + Innosoft + May 1998 + + + IMAP4 Namespace + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (1998). All Rights Reserved. + +1. Abstract + + IMAP4 [RFC-2060] does not define a default server namespace. As a + result, two common namespace models have evolved: + + The "Personal Mailbox" model, in which the default namespace that is + presented consists of only the user's personal mailboxes. To access + shared mailboxes, the user must use an escape mechanism to reach + another namespace. + + The "Complete Hierarchy" model, in which the default namespace that + is presented includes the user's personal mailboxes along with any + other mailboxes they have access to. + + These two models, create difficulties for certain client operations. + This document defines a NAMESPACE command that allows a client to + discover the prefixes of namespaces used by a server for personal + mailboxes, other users' mailboxes, and shared mailboxes. This allows + a client to avoid much of the manual user configuration that is now + necessary when mixing and matching IMAP4 clients and servers. + +2. Conventions used in this document + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. If such lines are wrapped without a new "C:" or + "S:" label, then the wrapping is for editorial clarity and is not + part of the command. + + + +Gahrns & Newman Standards Track [Page 1] + +RFC 2342 IMAP4 Namespace May 1998 + + + Personal Namespace: A namespace that the server considers within the + personal scope of the authenticated user on a particular connection. + Typically, only the authenticated user has access to mailboxes in + their Personal Namespace. It is the part of the namespace that + belongs to the user that is allocated for mailboxes. If an INBOX + exists for a user, it MUST appear within the user's personal + namespace. In the typical case, there SHOULD be only one Personal + Namespace on a server. + + Other Users' Namespace: A namespace that consists of mailboxes from + the Personal Namespaces of other users. To access mailboxes in the + Other Users' Namespace, the currently authenticated user MUST be + explicitly granted access rights. For example, it is common for a + manager to grant to their secretary access rights to their mailbox. + In the typical case, there SHOULD be only one Other Users' Namespace + on a server. + + Shared Namespace: A namespace that consists of mailboxes that are + intended to be shared amongst users and do not exist within a user's + Personal Namespace. + + The namespaces a server uses MAY differ on a per-user basis. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC-2119]. + +3. Introduction and Overview + + Clients often attempt to create mailboxes for such purposes as + maintaining a record of sent messages (e.g. "Sent Mail") or + temporarily saving messages being composed (e.g. "Drafts"). For + these clients to inter-operate correctly with the variety of IMAP4 + servers available, the user must enter the prefix of the Personal + Namespace used by the server. Using the NAMESPACE command, a client + is able to automatically discover this prefix without manual user + configuration. + + In addition, users are often required to manually enter the prefixes + of various namespaces in order to view the mailboxes located there. + For example, they might be required to enter the prefix of #shared to + view the shared mailboxes namespace. The NAMESPACE command allows a + client to automatically discover the namespaces that are available on + a server. This allows a client to present the available namespaces to + the user in what ever manner it deems appropriate. For example, a + + + + + + +Gahrns & Newman Standards Track [Page 2] + +RFC 2342 IMAP4 Namespace May 1998 + + + client could choose to initially display only personal mailboxes, or + it may choose to display the complete list of mailboxes available, + and initially position the user at the root of their Personal + Namespace. + + A server MAY choose to make available to the NAMESPACE command only a + subset of the complete set of namespaces the server supports. To + provide the ability to access these namespaces, a client SHOULD allow + the user the ability to manually enter a namespace prefix. + +4. Requirements + + IMAP4 servers that support this extension MUST list the keyword + NAMESPACE in their CAPABILITY response. + + The NAMESPACE command is valid in the Authenticated and Selected + state. + +5. NAMESPACE Command + + Arguments: none + + Response: an untagged NAMESPACE response that contains the prefix + and hierarchy delimiter to the server's Personal + Namespace(s), Other Users' Namespace(s), and Shared + Namespace(s) that the server wishes to expose. The + response will contain a NIL for any namespace class + that is not available. Namespace_Response_Extensions + MAY be included in the response. + Namespace_Response_Extensions which are not on the IETF + standards track, MUST be prefixed with an "X-". + + Result: OK - Command completed + NO - Error: Can't complete command + BAD - argument invalid + + Example 5.1: + =========== + + < A server that supports a single personal namespace. No leading + prefix is used on personal mailboxes and "/" is the hierarchy + delimiter.> + + C: A001 NAMESPACE + S: * NAMESPACE (("" "/")) NIL NIL + S: A001 OK NAMESPACE command completed + + + + + +Gahrns & Newman Standards Track [Page 3] + +RFC 2342 IMAP4 Namespace May 1998 + + + Example 5.2: + =========== + + < A user logged on anonymously to a server. No personal mailboxes + are associated with the anonymous user and the user does not have + access to the Other Users' Namespace. No prefix is required to + access shared mailboxes and the hierarchy delimiter is "." > + + C: A001 NAMESPACE + S: * NAMESPACE NIL NIL (("" ".")) + S: A001 OK NAMESPACE command completed + + Example 5.3: + =========== + + < A server that contains a Personal Namespace and a single Shared + Namespace. > + + C: A001 NAMESPACE + S: * NAMESPACE (("" "/")) NIL (("Public Folders/" "/")) + S: A001 OK NAMESPACE command completed + + Example 5.4: + =========== + + < A server that contains a Personal Namespace, Other Users' + Namespace and multiple Shared Namespaces. Note that the hierarchy + delimiter used within each namespace can be different. > + + C: A001 NAMESPACE + S: * NAMESPACE (("" "/")) (("~" "/")) (("#shared/" "/") + ("#public/" "/")("#ftp/" "/")("#news." ".")) + S: A001 OK NAMESPACE command completed + + The prefix string allows a client to do things such as automatically + creating personal mailboxes or LISTing all available mailboxes within + a namespace. + + Example 5.5: + =========== + + < A server that supports only the Personal Namespace, with a + leading prefix of INBOX to personal mailboxes and a hierarchy + delimiter of "."> + + C: A001 NAMESPACE + S: * NAMESPACE (("INBOX." ".")) NIL NIL + S: A001 OK NAMESPACE command completed + + + +Gahrns & Newman Standards Track [Page 4] + +RFC 2342 IMAP4 Namespace May 1998 + + + < Automatically create a mailbox to store sent items.> + + C: A002 CREATE "INBOX.Sent Mail" + S: A002 OK CREATE command completed + + Although typically a server will support only a single Personal + Namespace, and a single Other User's Namespace, circumstances exist + where there MAY be multiples of these, and a client MUST be prepared + for them. If a client is configured such that it is required to + create a certain mailbox, there can be circumstances where it is + unclear which Personal Namespaces it should create the mailbox in. + In these situations a client SHOULD let the user select which + namespaces to create the mailbox in. + + Example 5.6: + =========== + + < In this example, a server supports 2 Personal Namespaces. In + addition to the regular Personal Namespace, the user has an + additional personal namespace to allow access to mailboxes in an + MH format mailstore. > + + < The client is configured to save a copy of all mail sent by the + user into a mailbox called 'Sent Mail'. Furthermore, after a + message is deleted from a mailbox, the client is configured to + move that message to a mailbox called 'Deleted Items'.> + + < Note that this example demonstrates how some extension flags can + be passed to further describe the #mh namespace. > + + C: A001 NAMESPACE + S: * NAMESPACE (("" "/")("#mh/" "/" "X-PARAM" ("FLAG1" "FLAG2"))) + NIL NIL + S: A001 OK NAMESPACE command completed + + < It is desired to keep only one copy of sent mail. It is unclear + which Personal Namespace the client should use to create the 'Sent + Mail' mailbox. The user is prompted to select a namespace and + only one 'Sent Mail' mailbox is created. > + + C: A002 CREATE "Sent Mail" + S: A002 OK CREATE command completed + + < The client is designed so that it keeps two 'Deleted Items' + mailboxes, one for each namespace. > + + C: A003 CREATE "Delete Items" + S: A003 OK CREATE command completed + + + +Gahrns & Newman Standards Track [Page 5] + +RFC 2342 IMAP4 Namespace May 1998 + + + C: A004 CREATE "#mh/Deleted Items" + S: A004 OK CREATE command completed + + The next level of hierarchy following the Other Users' Namespace + prefix SHOULD consist of <username>, where <username> is a user name + as per the IMAP4 LOGIN or AUTHENTICATE command. + + A client can construct a LIST command by appending a "%" to the Other + Users' Namespace prefix to discover the Personal Namespaces of other + users that are available to the currently authenticated user. + + In response to such a LIST command, a server SHOULD NOT return user + names that have not granted access to their personal mailboxes to the + user in question. + + A server MAY return a LIST response containing only the names of + users that have explicitly granted access to the user in question. + + Alternatively, a server MAY return NO to such a LIST command, + requiring that a user name be included with the Other Users' + Namespace prefix before listing any other user's mailboxes. + + Example 5.7: + =========== + + < A server that supports providing a list of other user's + mailboxes that are accessible to the currently logged on user. > + + C: A001 NAMESPACE + S: * NAMESPACE (("" "/")) (("Other Users/" "/")) NIL + S: A001 OK NAMESPACE command completed + + C: A002 LIST "" "Other Users/%" + S: * LIST () "/" "Other Users/Mike" + S: * LIST () "/" "Other Users/Karen" + S: * LIST () "/" "Other Users/Matthew" + S: * LIST () "/" "Other Users/Tesa" + S: A002 OK LIST command completed + + Example 5.8: + =========== + + < A server that does not support providing a list of other user's + mailboxes that are accessible to the currently logged on user. + The mailboxes are listable if the client includes the name of the + other user with the Other Users' Namespace prefix. > + + + + + +Gahrns & Newman Standards Track [Page 6] + +RFC 2342 IMAP4 Namespace May 1998 + + + C: A001 NAMESPACE + S: * NAMESPACE (("" "/")) (("#Users/" "/")) NIL + S: A001 OK NAMESPACE command completed + + < In this example, the currently logged on user has access to the + Personal Namespace of user Mike, but the server chose to suppress + this information in the LIST response. However, by appending the + user name Mike (received through user input) to the Other Users' + Namespace prefix, the client is able to get a listing of the + personal mailboxes of user Mike. > + + C: A002 LIST "" "#Users/%" + S: A002 NO The requested item could not be found. + + C: A003 LIST "" "#Users/Mike/%" + S: * LIST () "/" "#Users/Mike/INBOX" + S: * LIST () "/" "#Users/Mike/Foo" + S: A003 OK LIST command completed. + + A prefix string might not contain a hierarchy delimiter, because + in some cases it is not needed as part of the prefix. + + Example 5.9: + =========== + + < A server that allows access to the Other Users' Namespace by + prefixing the others' mailboxes with a '~' followed by <username>, + where <username> is a user name as per the IMAP4 LOGIN or + AUTHENTICATE command.> + + C: A001 NAMESPACE + S: * NAMESPACE (("" "/")) (("~" "/")) NIL + S: A001 OK NAMESPACE command completed + + < List the mailboxes for user mark > + + C: A002 LIST "" "~mark/%" + S: * LIST () "/" "~mark/INBOX" + S: * LIST () "/" "~mark/foo" + S: A002 OK LIST command completed + + Historical convention has been to start all namespaces with the "#" + character. Namespaces that include the "#" character are not IMAP + URL [IMAP-URL] friendly requiring the "#" character to be represented + as %23 when within URLs. As such, server implementers MAY instead + consider using namespace prefixes that do not contain the "#" + character. + + + + +Gahrns & Newman Standards Track [Page 7] + +RFC 2342 IMAP4 Namespace May 1998 + + +6. Formal Syntax + + The following syntax specification uses the augmented Backus-Naur + Form (BNF) as described in [ABNF]. + + atom = <atom> + ; <atom> as defined in [RFC-2060] + + Namespace = nil / "(" 1*( "(" string SP (<"> QUOTED_CHAR <"> / + nil) *(Namespace_Response_Extension) ")" ) ")" + + Namespace_Command = "NAMESPACE" + + Namespace_Response_Extension = SP string SP "(" string *(SP string) + ")" + + Namespace_Response = "*" SP "NAMESPACE" SP Namespace SP Namespace SP + Namespace + + ; The first Namespace is the Personal Namespace(s) + ; The second Namespace is the Other Users' Namespace(s) + ; The third Namespace is the Shared Namespace(s) + + nil = <nil> + ; <nil> as defined in [RFC-2060] + + QUOTED_CHAR = <QUOTED_CHAR> + ; <QUOTED_CHAR> as defined in [RFC-2060] + + string = <string> + ; <string> as defined in [RFC-2060] + ; Note that the namespace prefix is to a mailbox and following + ; IMAP4 convention, any international string in the NAMESPACE + ; response MUST be of modified UTF-7 format as described in + ; [RFC-2060]. + +7. Security Considerations + + In response to a LIST command containing an argument of the Other + Users' Namespace prefix, a server SHOULD NOT list users that have not + granted list access to their personal mailboxes to the currently + authenticated user. Providing such a list, could compromise security + by potentially disclosing confidential information of who is located + on the server, or providing a starting point of a list of user + accounts to attack. + + + + + + +Gahrns & Newman Standards Track [Page 8] + +RFC 2342 IMAP4 Namespace May 1998 + + +8. References + + [RFC-2060], Crispin, M., "Internet Message Access Protocol Version + 4rev1", RFC 2060, December 1996. + + [RFC-2119], Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [ABNF] Crocker, D., Editor, and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 2234, November 1997. + + [IMAP-URL], Newman, C., "IMAP URL Scheme", RFC 2192, September 1997. + +9. Acknowledgments + + Many people have participated in the discussion of IMAP namespaces on + the IMAP mailing list. In particular, the authors would like to + thank Mark Crispin for many of the concepts relating to the Personal + Namespace and accessing the Personal Namespace of other users, Steve + Hole for summarizing the two namespace models, John Myers and Jack De + Winter for their work in a preceding effort trying to define a + standardized personal namespace, and Larry Osterman for his review + and collaboration on this document. + +11. Authors' Addresses + + Mike Gahrns + Microsoft + One Microsoft Way + Redmond, WA, 98072, USA + + Phone: (425) 936-9833 + EMail: mikega@microsoft.com + + + Chris Newman + Innosoft International, Inc. + 1050 East Garvey Ave. South + West Covina, CA, 91790, USA + + EMail: chris.newman@innosoft.com + + + + + + + + + + +Gahrns & Newman Standards Track [Page 9] + +RFC 2342 IMAP4 Namespace May 1998 + + +12. Full Copyright Statement + + Copyright (C) The Internet Society (1998). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. + + This document and the information contained herein is provided on an + "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING + TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING + BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION + HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF + MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + + + + + + + + + + + + + + + + + + + + + + + + +Gahrns & Newman Standards Track [Page 10] + diff --git a/imap/docs/rfc/rfc2683.txt b/imap/docs/rfc/rfc2683.txt new file mode 100644 index 00000000..d92e3405 --- /dev/null +++ b/imap/docs/rfc/rfc2683.txt @@ -0,0 +1,1291 @@ + + + + + + +Network Working Group B. Leiba +Request for Comments: 2683 IBM T.J. Watson Research Center +Category: Informational September 1999 + + + IMAP4 Implementation Recommendations + +Status of this Memo + + This memo provides information for the Internet community. It does + not specify an Internet standard of any kind. Distribution of this + memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (1999). All Rights Reserved. + +1. Abstract + + The IMAP4 specification [RFC-2060] describes a rich protocol for use + in building clients and servers for storage, retrieval, and + manipulation of electronic mail. Because the protocol is so rich and + has so many implementation choices, there are often trade-offs that + must be made and issues that must be considered when designing such + clients and servers. This document attempts to outline these issues + and to make recommendations in order to make the end products as + interoperable as possible. + +2. Conventions used in this document + + In examples, "C:" indicates lines sent by a client that is connected + to a server. "S:" indicates lines sent by the server to the client. + + The words "must", "must not", "should", "should not", and "may" are + used with specific meaning in this document; since their meaning is + somewhat different from that specified in RFC 2119, we do not put + them in all caps here. Their meaning is as follows: + + must -- This word means that the action described is necessary + to ensure interoperability. The recommendation should + not be ignored. + must not -- This phrase means that the action described will be + almost certain to hurt interoperability. The + recommendation should not be ignored. + + + + + + + +Leiba Informational [Page 1] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + should -- This word means that the action described is strongly + recommended and will enhance interoperability or + usability. The recommendation should not be ignored + without careful consideration. + should not -- This phrase means that the action described is strongly + recommended against, and might hurt interoperability or + usability. The recommendation should not be ignored + without careful consideration. + may -- This word means that the action described is an + acceptable implementation choice. No specific + recommendation is implied; this word is used to point + out a choice that might not be obvious, or to let + implementors know what choices have been made by + existing implementations. + +3. Interoperability Issues and Recommendations + +3.1. Accessibility + + This section describes the issues related to access to servers and + server resources. Concerns here include data sharing and maintenance + of client/server connections. + +3.1.1. Multiple Accesses of the Same Mailbox + + One strong point of IMAP4 is that, unlike POP3, it allows for + multiple simultaneous access to a single mailbox. A user can, thus, + read mail from a client at home while the client in the office is + still connected; or the help desk staff can all work out of the same + inbox, all seeing the same pool of questions. An important point + about this capability, though is that NO SERVER IS GUARANTEED TO + SUPPORT THIS. If you are selecting an IMAP server and this facility + is important to you, be sure that the server you choose to install, + in the configuration you choose to use, supports it. + + If you are designing a client, you must not assume that you can + access the same mailbox more than once at a time. That means + + 1. you must handle gracefully the failure of a SELECT command if the + server refuses the second SELECT, + 2. you must handle reasonably the severing of your connection (see + "Severed Connections", below) if the server chooses to allow the + second SELECT by forcing the first off, + 3. you must avoid making multiple connections to the same mailbox in + your own client (for load balancing or other such reasons), and + 4. you must avoid using the STATUS command on a mailbox that you have + selected (with some server implementations the STATUS command has + the same problems with multiple access as do the SELECT and + + + +Leiba Informational [Page 2] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + EXAMINE commands). + + A further note about STATUS: The STATUS command is sometimes used to + check a non-selected mailbox for new mail. This mechanism must not + be used to check for new mail in the selected mailbox; section 5.2 of + [RFC-2060] specifically forbids this in its last paragraph. Further, + since STATUS takes a mailbox name it is an independent operation, not + operating on the selected mailbox. Because of this, the information + it returns is not necessarily in synchronization with the selected + mailbox state. + +3.1.2. Severed Connections + + The client/server connection may be severed for one of three reasons: + the client severs the connection, the server severs the connection, + or the connection is severed by outside forces beyond the control of + the client and the server (a telephone line drops, for example). + Clients and servers must both deal with these situations. + + When the client wants to sever a connection, it's usually because it + has finished the work it needed to do on that connection. The client + should send a LOGOUT command, wait for the tagged response, and then + close the socket. But note that, while this is what's intended in + the protocol design, there isn't universal agreement here. Some + contend that sending the LOGOUT and waiting for the two responses + (untagged BYE and tagged OK) is wasteful and unnecessary, and that + the client can simply close the socket. The server should interpret + the closed socket as a log out by the client. The counterargument is + that it's useful from the standpoint of cleanup, problem + determination, and the like, to have an explicit client log out, + because otherwise there is no way for the server to tell the + difference between "closed socket because of log out" and "closed + socket because communication was disrupted". If there is a + client/server interaction problem, a client which routinely + terminates a session by breaking the connection without a LOGOUT will + make it much more difficult to determine the problem. + + Because of this disagreement, server designers must be aware that + some clients might close the socket without sending a LOGOUT. In any + case, whether or not a LOGOUT was sent, the server should not + implicitly expunge any messages from the selected mailbox. If a + client wants the server to do so, it must send a CLOSE or EXPUNGE + command explicitly. + + When the server wants to sever a connection it's usually due to an + inactivity timeout or is because a situation has arisen that has + changed the state of the mail store in a way that the server can not + communicate to the client. The server should send an untagged BYE + + + +Leiba Informational [Page 3] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + response to the client and then close the socket. Sending an + untagged BYE response before severing allows the server to send a + human-readable explanation of the problem to the client, which the + client may then log, display to the user, or both (see section 7.1.5 + of [RFC-2060]). + + Regarding inactivity timeouts, there is some controversy. Unlike + POP, for which the design is for a client to connect, retrieve mail, + and log out, IMAP's design encourages long-lived (and mostly + inactive) client/server sessions. As the number of users grows, this + can use up a lot of server resources, especially with clients that + are designed to maintain sessions for mailboxes that the user has + finished accessing. To alleviate this, a server may implement an + inactivity timeout, unilaterally closing a session (after first + sending an untagged BYE, as noted above). Some server operators have + reported dramatic improvements in server performance after doing + this. As specified in [RFC-2060], if such a timeout is done it must + not be until at least 30 minutes of inactivity. The reason for this + specification is to prevent clients from sending commands (such as + NOOP) to the server at frequent intervals simply to avert a too-early + timeout. If the client knows that the server may not time out the + session for at least 30 minutes, then the client need not poll at + intervals more frequent than, say, 25 minutes. + +3.2. Scaling + + IMAP4 has many features that allow for scalability, as mail stores + become larger and more numerous. Large numbers of users, mailboxes, + and messages, and very large messages require thought to handle + efficiently. This document will not address the administrative + issues involved in large numbers of users, but we will look at the + other items. + +3.2.1. Flood Control + + There are three situations when a client can make a request that will + result in a very large response - too large for the client reasonably + to deal with: there are a great many mailboxes available, there are a + great many messages in the selected mailbox, or there is a very large + message part. The danger here is that the end user will be stuck + waiting while the server sends (and the client processes) an enormous + response. In all of these cases there are things a client can do to + reduce that danger. + + There is also the case where a client can flood a server, by sending + an arbitratily long command. We'll discuss that issue, too, in this + section. + + + + +Leiba Informational [Page 4] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + +3.2.1.1. Listing Mailboxes + + Some servers present Usenet newsgroups to IMAP users. Newsgroups, + and other such hierarchical mailbox structures, can be very numerous + but may have only a few entries at the top level of hierarchy. Also, + some servers are built against mail stores that can, unbeknownst to + the server, have circular hierarchies - that is, it's possible for + "a/b/c/d" to resolve to the same file structure as "a", which would + then mean that "a/b/c/d/b" is the same as "a/b", and the hierarchy + will never end. The LIST response in this case will be unlimited. + + Clients that will have trouble with this are those that use + + C: 001 LIST "" * + + to determine the mailbox list. Because of this, clients should not + use an unqualified "*" that way in the LIST command. A safer + approach is to list each level of hierarchy individually, allowing + the user to traverse the tree one limb at a time, thus: + + C: 001 LIST "" % + S: * LIST () "/" Banana + S: * LIST ...etc... + S: 001 OK done + + and then + + C: 002 LIST "" Banana/% + S: * LIST () "/" Banana/Apple + S: * LIST ...etc... + S: 002 OK done + + Using this technique the client's user interface can give the user + full flexibility without choking on the voluminous reply to "LIST *". + + Of course, it is still possible that the reply to + + C: 005 LIST "" alt.fan.celebrity.% + + may be thousands of entries long, and there is, unfortunately, + nothing the client can do to protect itself from that. This has not + yet been a notable problem. + + Servers that may export circular hierarchies (any server that + directly presents a UNIX file system, for instance) should limit the + hierarchy depth to prevent unlimited LIST responses. A suggested + depth limit is 20 hierarchy levels. + + + + +Leiba Informational [Page 5] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + +3.2.1.2. Fetching the List of Messages + + When a client selects a mailbox, it is given a count, in the untagged + EXISTS response, of the messages in the mailbox. This number can be + very large. In such a case it might be unwise to use + + C: 004 FETCH 1:* ALL + + to populate the user's view of the mailbox. One good method to avoid + problems with this is to batch the requests, thus: + + C: 004 FETCH 1:50 ALL + S: * 1 FETCH ...etc... + S: 004 OK done + C: 005 FETCH 51:100 ALL + S: * 51 FETCH ...etc... + S: 005 OK done + C: 006 FETCH 101:150 ALL + ...etc... + + Using this method, another command, such as "FETCH 6 BODY[1]" can be + inserted as necessary, and the client will not have its access to the + server blocked by a storm of FETCH replies. (Such a method could be + reversed to fetch the LAST 50 messages first, then the 50 prior to + that, and so on.) + + As a smart extension of this, a well designed client, prepared for + very large mailboxes, will not automatically fetch data for all + messages AT ALL. Rather, the client will populate the user's view + only as the user sees it, possibly pre-fetching selected information, + and only fetching other information as the user scrolls to it. For + example, to select only those messages beginning with the first + unseen one: + + C: 003 SELECT INBOX + S: * 10000 EXISTS + S: * 80 RECENT + S: * FLAGS (\Answered \Flagged \Deleted \Draft \Seen) + S: * OK [UIDVALIDITY 824708485] UID validity status + S: * OK [UNSEEN 9921] First unseen message + S: 003 OK [READ-WRITE] SELECT completed + C: 004 FETCH 9921:* ALL + ... etc... + + If the server does not return an OK [UNSEEN] response, the client may + use SEARCH UNSEEN to obtain that value. + + + + + +Leiba Informational [Page 6] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + This mechanism is good as a default presentation method, but only + works well if the default message order is acceptable. A client may + want to present various sort orders to the user (by subject, by date + sent, by sender, and so on) and in that case (lacking a SORT + extension on the server side) the client WILL have to retrieve all + message descriptors. A client that provides this service should not + do it by default and should inform the user of the costs of choosing + this option for large mailboxes. + +3.2.1.3. Fetching a Large Body Part + + The issue here is similar to the one for a list of messages. In the + BODYSTRUCTURE response the client knows the size, in bytes, of the + body part it plans to fetch. Suppose this is a 70 MB video clip. The + client can use partial fetches to retrieve the body part in pieces, + avoiding the problem of an uninterruptible 70 MB literal coming back + from the server: + + C: 022 FETCH 3 BODY[1]<0.20000> + S: * 3 FETCH (FLAGS(\Seen) BODY[1]<0> {20000} + S: ...data...) + S: 022 OK done + C: 023 FETCH 3 BODY[1]<20001.20000> + S: * 3 FETCH (BODY[1]<20001> {20000} + S: ...data...) + S: 023 OK done + C: 024 FETCH 3 BODY[1]<40001.20000> + ...etc... + +3.2.1.4. BODYSTRUCTURE vs. Entire Messages + + Because FETCH BODYSTRUCTURE is necessary in order to determine the + number of body parts, and, thus, whether a message has "attachments", + clients often use FETCH FULL as their normal method of populating the + user's view of a mailbox. The benefit is that the client can display + a paperclip icon or some such indication along with the normal + message summary. However, this comes at a significant cost with some + server configurations. The parsing needed to generate the FETCH + BODYSTRUCTURE response may be time-consuming compared with that + needed for FETCH ENVELOPE. The client developer should consider this + issue when deciding whether the ability to add a paperclip icon is + worth the tradeoff in performance, especially with large mailboxes. + + Some clients, rather than using FETCH BODYSTRUCTURE, use FETCH BODY[] + (or the equivalent FETCH RFC822) to retrieve the entire message. + They then do the MIME parsing in the client. This may give the + client slightly more flexibility in some areas (access, for instance, + to header fields that aren't returned in the BODYSTRUCTURE and + + + +Leiba Informational [Page 7] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + ENVELOPE responses), but it can cause severe performance problems by + forcing the transfer of all body parts when the user might only want + to see some of them - a user logged on by modem and reading a small + text message with a large ZIP file attached may prefer to read the + text only and save the ZIP file for later. Therefore, a client + should not normally retrieve entire messages and should retrieve + message body parts selectively. + +3.2.1.5. Long Command Lines + + A client can wind up building a very long command line in an effort to + try to be efficient about requesting information from a server. This + can typically happen when a client builds a message set from selected + messages and doesn't recognise that contiguous blocks of messages may + be group in a range. Suppose a user selects all 10,000 messages in a + large mailbox and then unselects message 287. The client could build + that message set as "1:286,288:10000", but a client that doesn't + handle that might try to enumerate each message individually and build + "1,2,3,4, [and so on] ,9999,10000". Adding that to the fetch command + results in a command line that's almost 49,000 octets long, and, + clearly, one can construct a command line that's even longer. + + A client should limit the length of the command lines it generates to + approximately 1000 octets (including all quoted strings but not + including literals). If the client is unable to group things into + ranges so that the command line is within that length, it should + split the request into multiple commands. The client should use + literals instead of long quoted strings, in order to keep the command + length down. + + For its part, a server should allow for a command line of at least + 8000 octets. This provides plenty of leeway for accepting reasonable + length commands from clients. The server should send a BAD response + to a command that does not end within the server's maximum accepted + command length. + +3.2.2. Subscriptions + + The client isn't the only entity that can get flooded: the end user, + too, may need some flood control. The IMAP4 protocol provides such + control in the form of subscriptions. Most servers support the + SUBSCRIBE, UNSUBSCRIBE, and LSUB commands, and many users choose to + narrow down a large list of available mailboxes by subscribing to the + ones that they usually want to see. Clients, with this in mind, + should give the user a way to see only subscribed mailboxes. A + client that never uses the LSUB command takes a significant usability + feature away from the user. Of course, the client would not want to + hide the LIST command completely; the user needs to have a way to + + + +Leiba Informational [Page 8] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + choose between LIST and LSUB. The usual way to do this is to provide + a setting like "show which mailboxes?: [] all [] subscribed only". + +3.2.3. Searching + + IMAP SEARCH commands can become particularly troublesome (that is, + slow) on mailboxes containing a large number of messages. So let's + put a few things in perspective in that regard. + + The flag searches should be fast. The flag searches (ALL, [UN]SEEN, + [UN]ANSWERED, [UN]DELETED, [UN]DRAFT, [UN]FLAGGED, NEW, OLD, RECENT) + are known to be used by clients for the client's own use (for + instance, some clients use "SEARCH UNSEEN" to find unseen mail and + "SEARCH DELETED" to warn the user before expunging messages). + + Other searches, particularly the text searches (HEADER, TEXT, BODY) + are initiated by the user, rather than by the client itself, and + somewhat slower performance can be tolerated, since the user is aware + that the search is being done (and is probably aware that it might be + time-consuming). A smart server might use dynamic indexing to speed + commonly used text searches. + + The client may allow other commands to be sent to the server while a + SEARCH is in progress, but at the time of this writing there is + little or no server support for parallel processing of multiple + commands in the same session (and see "Multiple Accesses of the Same + Mailbox" above for a description of the dangers of trying to work + around this by doing your SEARCH in another session). + + Another word about text searches: some servers, built on database + back-ends with indexed search capabilities, may return search results + that do not match the IMAP spec's "case-insensitive substring" + requirements. While these servers are in violation of the protocol, + there is little harm in the violation as long as the search results + are used only in response to a user's request. Still, developers of + such servers should be aware that they ARE violating the protocol, + should think carefully about that behaviour, and must be certain that + their servers respond accurately to the flag searches for the reasons + outlined above. + + In addition, servers should support CHARSET UTF-8 [UTF-8] in + searches. + + + + + + + + + +Leiba Informational [Page 9] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + +3.3 Avoiding Invalid Requests + + IMAP4 provides ways for a server to tell a client in advance what is + and isn't permitted in some circumstances. Clients should use these + features to avoid sending requests that a well designed client would + know to be invalid. This section explains this in more detail. + +3.3.1. The CAPABILITY Command + + All IMAP4 clients should use the CAPABILITY command to determine what + version of IMAP and what optional features a server supports. The + client should not send IMAP4rev1 commands and arguments to a server + that does not advertize IMAP4rev1 in its CAPABILITY response. + Similarly, the client should not send IMAP4 commands that no longer + exist in IMAP4rev1 to a server that does not advertize IMAP4 in its + CAPABILITY response. An IMAP4rev1 server is NOT required to support + obsolete IMAP4 or IMAP2bis commands (though some do; do not let this + fact lull you into thinking that it's valid to send such commands to + an IMAP4rev1 server). + + A client should not send commands to probe for the existance of + certain extensions. All standard and standards-track extensions + include CAPABILITY tokens indicating their presense. All private and + experimental extensions should do the same, and clients that take + advantage of them should use the CAPABILITY response to determine + whether they may be used or not. + +3.3.2. Don't Do What the Server Says You Can't + + In many cases, the server, in response to a command, will tell the + client something about what can and can't be done with a particular + mailbox. The client should pay attention to this information and + should not try to do things that it's been told it can't do. + + Examples: + + * Do not try to SELECT a mailbox that has the \Noselect flag set. + * Do not try to CREATE a sub-mailbox in a mailbox that has the + \Noinferiors flag set. + * Do not respond to a failing COPY or APPEND command by trying to + CREATE the target mailbox if the server does not respond with a + [TRYCREATE] response code. + * Do not try to expunge a mailbox that has been selected with the + [READ-ONLY] response code. + + + + + + + +Leiba Informational [Page 10] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + +3.4. Miscellaneous Protocol Considerations + + We describe here a number of important protocol-related issues, the + misunderstanding of which has caused significant interoperability + problems in IMAP4 implementations. One general item is that every + implementer should be certain to take note of and to understand + section 2.2.2 and the preamble to section 7 of the IMAP4rev1 spec + [RFC-2060]. + +3.4.1. Well Formed Protocol + + We cannot stress enough the importance of adhering strictly to the + protocol grammar. The specification of the protocol is quite rigid; + do not assume that you can insert blank space for "readability" if + none is called for. Keep in mind that there are parsers out there + that will crash if there are protocol errors. There are clients that + will report every parser burp to the user. And in any case, + information that cannot be parsed is information that is lost. Be + careful in your protocol generation. And see "A Word About Testing", + below. + + In particular, note that the string in the INTERNALDATE response is + NOT an RFC-822 date string - that is, it is not in the same format as + the first string in the ENVELOPE response. Since most clients will, + in fact, accept an RFC-822 date string in the INTERNALDATE response, + it's easy to miss this in your interoperability testing. But it will + cause a problem with some client, so be sure to generate the correct + string for this field. + +3.4.2. Special Characters + + Certain characters, currently the double-quote and the backslash, may + not be sent as-is inside a quoted string. These characters must be + preceded by the escape character if they are in a quoted string, or + else the string must be sent as a literal. Both clients and servers + must handle this, both on output (they must send these characters + properly) and on input (they must be able to receive escaped + characters in quoted strings). Example: + + C: 001 LIST "" % + S: * LIST () "" INBOX + S: * LIST () "\\" TEST + S: * LIST () "\\" {12} + S: "My" mailbox + S: 001 OK done + C: 002 LIST "" "\"My\" mailbox\\%" + S: * LIST () "\\" {17} + S: "My" mailbox\Junk + + + +Leiba Informational [Page 11] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + S: 002 OK done + + Note that in the example the server sent the hierarchy delimiter as + an escaped character in the quoted string and sent the mailbox name + containing imbedded double-quotes as a literal. The client used only + quoted strings, escaping both the backslash and the double-quote + characters. + + The CR and LF characters may be sent ONLY in literals; they are not + allowed, even if escaped, inside quoted strings. + + And while we're talking about special characters: the IMAP spec, in + the section titled "Mailbox International Naming Convention", + describes how to encode mailbox names in modified UTF-7 [UTF-7 and + RFC-2060]. Implementations must adhere to this in order to be + interoperable in the international market, and servers should + validate mailbox names sent by client and reject names that do not + conform. + + As to special characters in userids and passwords: clients must not + restrict what a user may type in for a userid or a password. The + formal grammar specifies that these are "astrings", and an astring + can be a literal. A literal, in turn can contain any 8-bit + character, and clients must allow users to enter all 8-bit characters + here, and must pass them, unchanged, to the server (being careful to + send them as literals when necessary). In particular, some server + configurations use "@" in user names, and some clients do not allow + that character to be entered; this creates a severe interoperability + problem. + +3.4.3. UIDs and UIDVALIDITY + + Servers that support existing back-end mail stores often have no good + place to save UIDs for messages. Often the existing mail store will + not have the concept of UIDs in the sense that IMAP has: strictly + increasing, never re-issued, 32-bit integers. Some servers solve + this by storing the UIDs in a place that's accessible to end users, + allowing for the possibility that the users will delete them. Others + solve it by re-assigning UIDs every time a mailbox is selected. + + The server should maintain UIDs permanently for all messages if it + can. If that's not possible, the server must change the UIDVALIDITY + value for the mailbox whenever any of the UIDs may have become + invalid. Clients must recognize that the UIDVALIDITY has changed and + must respond to that condition by throwing away any information that + they have saved about UIDs in that mailbox. There have been many + problems in this area when clients have failed to do this; in the + worst case it will result in loss of mail when a client deletes the + + + +Leiba Informational [Page 12] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + wrong piece of mail by using a stale UID. + + It seems to be a common misunderstanding that "the UIDVALIDITY and + the UID, taken together, form a 64-bit identifier that uniquely + identifies a message on a server". This is absolutely NOT TRUE. + There is no assurance that the UIDVALIDITY values of two mailboxes be + different, so the UIDVALIDITY in no way identifies a mailbox. The + ONLY purpose of UIDVALIDITY is, as its name indicates, to give the + client a way to check the validity of the UIDs it has cached. While + it is a valid implementation choice to put these values together to + make a 64-bit identifier for the message, the important concept here + is that UIDs are not unique between mailboxes; they are only unique + WITHIN a given mailbox. + + Some server implementations have attempted to make UIDs unique across + the entire server. This is inadvisable, in that it limits the life + of UIDs unnecessarily. The UID is a 32-bit number and will run out + in reasonably finite time if it's global across the server. If you + assign UIDs sequentially in one mailbox, you will not have to start + re-using them until you have had, at one time or another, 2**32 + different messages in that mailbox. In the global case, you will + have to reuse them once you have had, at one time or another, 2**32 + different messages in the entire mail store. Suppose your server has + around 8000 users registered (2**13). That gives an average of 2**19 + UIDs per user. Suppose each user gets 32 messages (2**5) per day. + That gives you 2**14 days (16000+ days = about 45 years) before you + run out. That may seem like enough, but multiply the usage just a + little (a lot of spam, a lot of mailing list subscriptions, more + users) and you limit yourself too much. + + What's worse is that if you have to wrap the UIDs, and, thus, you + have to change UIDVALIDITY and invalidate the UIDs in the mailbox, + you have to do it for EVERY mailbox in the system, since they all + share the same UID pool. If you assign UIDs per mailbox and you have + a problem, you only have to kill the UIDs for that one mailbox. + + Under extreme circumstances (and this is extreme, indeed), the server + may have to invalidate UIDs while a mailbox is in use by a client - + that is, the UIDs that the client knows about in its active mailbox + are no longer valid. In that case, the server must immediately + change the UIDVALIDITY and must communicate this to the client. The + server may do this by sending an unsolicited UIDVALIDITY message, in + the same form as in response to the SELECT command. Clients must be + prepared to handle such a message and the possibly coincident failure + of the command in process. For example: + + + + + + +Leiba Informational [Page 13] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + C: 032 UID STORE 382 +Flags.silent \Deleted + S: * OK [UIDVALIDITY 12345] New UIDVALIDITY value! + S: 032 NO UID command rejected because UIDVALIDITY changed! + C: ...invalidates local information and re-fetches... + C: 033 FETCH 1:* UID + ...etc... + + At the time of the writing of this document, the only server known to + do this does so only under the following condition: the client + selects INBOX, but there is not yet a physical INBOX file created. + Nonetheless, the SELECT succeeds, exporting an empty INBOX with a + temporary UIDVALIDITY of 1. While the INBOX remains selected, mail + is delivered to the user, which creates the real INBOX file and + assigns a permanent UIDVALIDITY (that is likely not to be 1). The + server reports the change of UIDVALIDITY, but as there were no + messages before, so no UIDs have actually changed, all the client + must do is accept the change in UIDVALIDITY. + + Alternatively, a server may force the client to re-select the + mailbox, at which time it will obtain a new UIDVALIDITY value. To do + this, the server closes this client session (see "Severed + Connections" above) and the client then reconnects and gets back in + synch. Clients must be prepared for either of these behaviours. + + We do not know of, nor do we anticipate the future existance of, a + server that changes UIDVALIDITY while there are existing messages, + but clients must be prepared to handle this eventuality. + +3.4.4. FETCH Responses + + When a client asks for certain information in a FETCH command, the + server may return the requested information in any order, not + necessarily in the order that it was requested. Further, the server + may return the information in separate FETCH responses and may also + return information that was not explicitly requested (to reflect to + the client changes in the state of the subject message). Some + examples: + + C: 001 FETCH 1 UID FLAGS INTERNALDATE + S: * 5 FETCH (FLAGS (\Deleted)) + S: * 1 FETCH (FLAGS (\Seen) INTERNALDATE "..." UID 345) + S: 001 OK done + + (In this case, the responses are in a different order. Also, the + server returned a flag update for message 5, which wasn't part of the + client's request.) + + + + + +Leiba Informational [Page 14] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + C: 002 FETCH 2 UID FLAGS INTERNALDATE + S: * 2 FETCH (INTERNALDATE "...") + S: * 2 FETCH (UID 399) + S: * 2 FETCH (FLAGS ()) + S: 002 OK done + + (In this case, the responses are in a different order and were + returned in separate responses.) + + C: 003 FETCH 2 BODY[1] + S: * 2 FETCH (FLAGS (\Seen) BODY[1] {14} + S: Hello world! + S: ) + S: 003 OK done + + (In this case, the FLAGS response was added by the server, since + fetching the body part caused the server to set the \Seen flag.) + + Because of this characteristic a client must be ready to receive any + FETCH response at any time and should use that information to update + its local information about the message to which the FETCH response + refers. A client must not assume that any FETCH responses will come + in any particular order, or even that any will come at all. If after + receiving the tagged response for a FETCH command the client finds + that it did not get all of the information requested, the client + should send a NOOP command to the server to ensure that the server + has an opportunity to send any pending EXPUNGE responses to the + client (see [RFC-2180]). + +3.4.5. RFC822.SIZE + + Some back-end mail stores keep the mail in a canonical form, rather + than retaining the original MIME format of the messages. This means + that the server must reassemble the message to produce a MIME stream + when a client does a fetch such as RFC822 or BODY[], requesting the + entire message. It also may mean that the server has no convenient + way to know the RFC822.SIZE of the message. Often, such a server + will actually have to build the MIME stream to compute the size, only + to throw the stream away and report the size to the client. + + When this is the case, some servers have chosen to estimate the size, + rather than to compute it precisely. Such an estimate allows the + client to display an approximate size to the user and to use the + estimate in flood control considerations (q.v.), but requires that + the client not use the size for things such as allocation of buffers, + because those buffers might then be too small to hold the actual MIME + stream. Instead, a client should use the size that's returned in the + literal when you fetch the data. + + + +Leiba Informational [Page 15] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + The protocol requires that the RFC822.SIZE value returned by the + server be EXACT. Estimating the size is a protocol violation, and + server designers must be aware that, despite the performance savings + they might realize in using an estimate, this practice will cause + some clients to fail in various ways. If possible, the server should + compute the RFC822.SIZE for a particular message once, and then save + it for later retrieval. If that's not possible, the server must + compute the value exactly every time. Incorrect estimates do cause + severe interoperability problems with some clients. + +3.4.6. Expunged Messages + + If the server allows multiple connections to the same mailbox, it is + often possible for messages to be expunged in one client unbeknownst + to another client. Since the server is not allowed to tell the + client about these expunged messages in response to a FETCH command, + the server may have to deal with the issue of how to return + information about an expunged message. There was extensive + discussion about this issue, and the results of that discussion are + summarized in [RFC-2180]. See that reference for a detailed + explanation and for recommendations. + +3.4.7. The Namespace Issue + + Namespaces are a very muddy area in IMAP4 implementation right now + (see [NAMESPACE] for a proposal to clear the water a bit). Until the + issue is resolved, the important thing for client developers to + understand is that some servers provide access through IMAP to more + than just the user's personal mailboxes, and, in fact, the user's + personal mailboxes may be "hidden" somewhere in the user's default + hierarchy. The client, therefore, should provide a setting wherein + the user can specify a prefix to be used when accessing mailboxes. If + the user's mailboxes are all in "~/mail/", for instance, then the + user can put that string in the prefix. The client would then put + the prefix in front of any name pattern in the LIST and LSUB + commands: + + C: 001 LIST "" ~/mail/% + + (See also "Reference Names in the LIST Command" below.) + +3.4.8. Creating Special-Use Mailboxes + + It may seem at first that this is part of the namespace issue; it is + not, and is only indirectly related to it. A number of clients like + to create special-use mailboxes with particular names. Most + commonly, clients with a "trash folder" model of message deletion + want to create a mailbox with the name "Trash" or "Deleted". Some + + + +Leiba Informational [Page 16] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + clients want to create a "Drafts" mailbox, an "Outbox" mailbox, or a + "Sent Mail" mailbox. And so on. There are two major + interoperability problems with this practice: + + 1. different clients may use different names for mailboxes with + similar functions (such as "Trash" and "Deleted"), or may manage + the same mailboxes in different ways, causing problems if a user + switches between clients and + 2. there is no guarantee that the server will allow the creation of + the desired mailbox. + + The client developer is, therefore, well advised to consider + carefully the creation of any special-use mailboxes on the server, + and, further, the client must not require such mailbox creation - + that is, if you do decide to do this, you must handle gracefully the + failure of the CREATE command and behave reasonably when your + special-use mailboxes do not exist and can not be created. + + In addition, the client developer should provide a convenient way for + the user to select the names for any special-use mailboxes, allowing + the user to make these names the same in all clients used and to put + them where the user wants them. + +3.4.9. Reference Names in the LIST Command + + Many implementers of both clients and servers are confused by the + "reference name" on the LIST command. The reference name is intended + to be used in much the way a "cd" (change directory) command is used + on Unix, PC DOS, Windows, and OS/2 systems. That is, the mailbox + name is interpreted in much the same way as a file of that name would + be found if one had done a "cd" command into the directory specified + by the reference name. For example, in Unix we have the following: + + > cd /u/jones/junk + > vi banana [file is "/u/jones/junk/banana"] + > vi stuff/banana [file is "/u/jones/junk/stuff/banana"] + > vi /etc/hosts [file is "/etc/hosts"] + + In the past, there have been several interoperability problems with + this. First, while some IMAP servers are built on Unix or PC file + systems, many others are not, and the file system semantics do not + make sense in those configurations. Second, while some IMAP servers + expose the underlying file system to the clients, others allow access + only to the user's personal mailboxes, or to some other limited set + of files, making such file-system-like semantics less meaningful. + Third, because the IMAP spec leaves the interpretation of the + reference name as "implementation-dependent", in the past the various + server implementations handled it in vastly differing ways. + + + +Leiba Informational [Page 17] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + The following recommendations are the result of significant + operational experience, and are intended to maximize + interoperability. + + Server implementations must implement the reference argument in a way + that matches the intended "change directory" operation as closely as + possible. As a minimum implementation, the reference argument may be + prepended to the mailbox name (while suppressing double delimiters; + see the next paragraph). Even servers that do not provide a way to + break out of the current hierarchy (see "breakout facility" below) + must provide a reasonable implementation of the reference argument, + as described here, so that they will interoperate with clients that + use it. + + Server implementations that prepend the reference argument to the + mailbox name should insert a hierarchy delimiter between them, and + must not insert a second if one is already present: + + C: A001 LIST ABC DEF + S: * LIST () "/" ABC/DEF <=== should do this + S: A001 OK done + + C: A002 LIST ABC/ /DEF + S: * LIST () "/" ABC//DEF <=== must not do this + S: A002 OK done + + On clients, the reference argument is chiefly used to implement a + "breakout facility", wherein the user may directly access a mailbox + outside the "current directory" hierarchy. Client implementations + should have an operational mode that does not use the reference + argument. This is to interoperate with older servers that did not + implement the reference argument properly. While it's a good idea to + give the user access to a breakout facility, clients that do not + intend to do so should not use the reference argument at all. + + Client implementations should always place a trailing hierarchy + delimiter on the reference argument. This is because some servers + prepend the reference argument to the mailbox name without inserting + a hierarchy delimiter, while others do insert a hierarchy delimiter + if one is not already present. A client that puts the delimiter in + will work with both varieties of server. + + Client implementations that implement a breakout facility should + allow the user to choose whether or not to use a leading hierarchy + delimiter on the mailbox argument. This is because the handling of a + leading mailbox hierarchy delimiter also varies from server to + server, and even between different mailstores on the same server. In + some cases, a leading hierarchy delimiter means "discard the + + + +Leiba Informational [Page 18] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + reference argument" (implementing the intended breakout facility), + thus: + + C: A001 LIST ABC/ /DEF + S: * LIST () "/" /DEF + S: A001 OK done + + In other cases, however, the two are catenated and the extra + hierarchy delimiter is discarded, thus: + + C: A001 LIST ABC/ /DEF + S: * LIST () "/" ABC/DEF + S: A001 OK done + + Client implementations must not assume that the server supports a + breakout facility, but may provide a way for the user to use one if + it is available. Any breakout facility should be exported to the + user interface. Note that there may be other "breakout" characters + besides the hierarchy delimiter (for instance, UNIX filesystem + servers are likely to use a leading "~" as well), and that their + interpretation is server-dependent. + +3.4.10. Mailbox Hierarchy Delimiters + + The server's selection of what to use as a mailbox hierarchy + delimiter is a difficult one, involving several issues: What + characters do users expect to see? What characters can they enter + for a hierarchy delimiter if it is desired (or required) that the + user enter it? What character can be used for the hierarchy + delimiter, noting that the chosen character can not otherwise be used + in the mailbox name? + + Because some interfaces show users the hierarchy delimiters or allow + users to enter qualified mailbox names containing them, server + implementations should use delimiter characters that users generally + expect to see as name separators. The most common characters used + for this are "/" (as in Unix file names), "\" (as in OS/2 and Windows + file names), and "." (as in news groups). There is little to choose + among these apart from what users may expect or what is dictated by + the underlying file system, if any. One consideration about using + "\" is that it's also a special character in the IMAP protocol. While + the use of other hierarchy delimiter characters is permissible, A + DESIGNER IS WELL ADVISED TO STAY WITH ONE FROM THIS SET unless the + server is intended for special purposes only. Implementers might be + thinking about using characters such as "-", "_", ";", "&", "#", "@", + and "!", but they should be aware of the surprise to the user as well + as of the effect on URLs and other external specifications (since + some of these characters have special meanings there). Also, a + + + +Leiba Informational [Page 19] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + server that uses "\" (and clients of such a server) must remember to + escape that character in quoted strings or to send literals instead. + Literals are recommended over escaped characters in quoted strings in + order to maintain compatibility with older IMAP versions that did not + allow escaped characters in quoted strings (but check the grammar to + see where literals are allowed): + + C: 001 LIST "" {13} + S: + send literal + C: this\%\%\%\h* + S: * LIST () "\\" {27} + S: this\is\a\mailbox\hierarchy + S: 001 OK LIST complete + + In any case, a server should not use normal alpha-numeric characters + (such as "X" or "0") as delimiters; a user would be very surprised to + find that "EXPENDITURES" actually represented a two-level hierarchy. + And a server should not use characters that are non-printable or + difficult or impossible to enter on a standard US keyboard. Control + characters, box-drawing characters, and characters from non-US + alphabets fit into this category. Their use presents + interoperability problems that are best avoided. + + The UTF-7 encoding of mailbox names also raises questions about what + to do with the hierarchy delimiters in encoded names: do we encode + each hierarchy level and separate them with delimiters, or do we + encode the fully qualified name, delimiters and all? The answer for + IMAP is the former: encode each hierarchy level separately, and + insert delimiters between. This makes it particularly important not + to use as a hierarchy delimiter a character that might cause + confusion with IMAP's modified UTF-7 [UTF-7 and RFC-2060] encoding. + + To repeat: a server should use "/", "\", or "." as its hierarchy + delimiter. The use of any other character is likely to cause + problems and is STRONGLY DISCOURAGED. + +3.4.11. ALERT Response Codes + + The protocol spec is very clear on the matter of what to do with + ALERT response codes, and yet there are many clients that violate it + so it needs to be said anyway: "The human-readable text contains a + special alert that must be presented to the user in a fashion that + calls the user's attention to the message." That should be clear + enough, but I'll repeat it here: Clients must present ALERT text + clearly to the user. + + + + + + +Leiba Informational [Page 20] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + +3.4.12. Deleting Mailboxes + + The protocol does not guarantee that a client may delete a mailbox + that is not empty, though on some servers it is permissible and is, + in fact, much faster than the alternative or deleting all the + messages from the client. If the client chooses to try to take + advantage of this possibility it must be prepared to use the other + method in the even that the more convenient one fails. Further, a + client should not try to delete the mailbox that it has selected, but + should first close that mailbox; some servers do not permit the + deletion of the selected mailbox. + + That said, a server should permit the deletion of a non-empty + mailbox; there's little reason to pass this work on to the client. + Moreover, forbidding this prevents the deletion of a mailbox that for + some reason can not be opened or expunged, leading to possible + denial-of-service problems. + + Example: + + [User tells the client to delete mailbox BANANA, which is + currently selected...] + C: 008 CLOSE + S: 008 OK done + C: 009 DELETE BANANA + S: 009 NO Delete failed; mailbox is not empty. + C: 010 SELECT BANANA + S: * ... untagged SELECT responses + S: 010 OK done + C: 011 STORE 1:* +FLAGS.SILENT \DELETED + S: 011 OK done + C: 012 CLOSE + S: 012 OK done + C: 013 DELETE BANANA + S: 013 OK done + +3.5. A Word About Testing + + Since the whole point of IMAP is interoperability, and since + interoperability can not be tested in a vacuum, the final + recommendation of this treatise is, "Test against EVERYTHING." Test + your client against every server you can get an account on. Test + your server with every client you can get your hands on. Many + clients make limited test versions available on the Web for the + downloading. Many server owners will give serious client developers + guest accounts for testing. Contact them and ask. NEVER assume that + because your client works with one or two servers, or because your + server does fine with one or two clients, you will interoperate well + + + +Leiba Informational [Page 21] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + + in general. + + In particular, in addition to everything else, be sure to test + against the reference implementations: the PINE client, the + University of Washington server, and the Cyrus server. + + See the following URLs on the web for more information here: + + IMAP Products and Sources: http://www.imap.org/products.html + IMC MailConnect: http://www.imc.org/imc-mailconnect + +4. Security Considerations + + This document describes behaviour of clients and servers that use the + IMAP4 protocol, and as such, has the same security considerations as + described in [RFC-2060]. + +5. References + + [RFC-2060] Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 2060, December 1996. + + [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC-2180] Gahrns, M., "IMAP4 Multi-Accessed Mailbox Practice", RFC + 2180, July 1997. + + [UTF-8] Yergeau, F., " UTF-8, a transformation format of Unicode + and ISO 10646", RFC 2044, October 1996. + + [UTF-7] Goldsmith, D. and M. Davis, "UTF-7, a Mail-Safe + Transformation Format of Unicode", RFC 2152, May 1997. + + [NAMESPACE] Gahrns, M. and C. Newman, "IMAP4 Namespace", Work in + Progress. + +6. Author's Address + + Barry Leiba + IBM T.J. Watson Research Center + 30 Saw Mill River Road + Hawthorne, NY 10532 + + Phone: 1-914-784-7941 + EMail: leiba@watson.ibm.com + + + + + +Leiba Informational [Page 22] + +RFC 2683 IMAP4 Implementation Recommendations September 1999 + + +7. Full Copyright Statement + + Copyright (C) The Internet Society (1999). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. + + This document and the information contained herein is provided on an + "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING + TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING + BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION + HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF + MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + + + + + + + + + + + + + +Leiba Informational [Page 23] + diff --git a/imap/docs/rfc/rfc2971.txt b/imap/docs/rfc/rfc2971.txt new file mode 100644 index 00000000..9e7264dc --- /dev/null +++ b/imap/docs/rfc/rfc2971.txt @@ -0,0 +1,451 @@ + + + + + + +Network Working Group T. Showalter +Request for Comments: 2971 Mirapoint, Inc. +Category: Standards Track October 2000 + + + IMAP4 ID extension + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2000). All Rights Reserved. + +Abstract + + The ID extension to the Internet Message Access Protocol - Version + 4rev1 (IMAP4rev1) protocol allows the server and client to exchange + identification information on their implementation in order to make + bug reports and usage statistics more complete. + +1. Introduction + + The IMAP4rev1 protocol described in [IMAP4rev1] provides a method for + accessing remote mail stores, but it provides no facility to + advertise what program a client or server uses to provide service. + This makes it difficult for implementors to get complete bug reports + from users, as it is frequently difficult to know what client or + server is in use. + + Additionally, some sites may wish to assemble usage statistics based + on what clients are used, but in an an environment where users are + permitted to obtain and maintain their own clients this is difficult + to accomplish. + + The ID command provides a facility to advertise information on what + programs are being used along with contact information (should bugs + ever occur). + + + + + + + + +Showalter Standards Track [Page 1] + +RFC 2971 IMAP4 ID extension October 2000 + + +2. Conventions Used in this Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [KEYWORDS]. + + The conventions used in this document are the same as specified in + [IMAP4rev1]. In examples, "C:" and "S:" indicate lines sent by the + client and server respectively. Line breaks have been inserted for + readability. + +3. Specification + + The sole purpose of the ID extension is to enable clients and servers + to exchange information on their implementations for the purposes of + statistical analysis and problem determination. + + This information is be submitted to a server by any client wishing to + provide information for statistical purposes, provided the server + advertises its willingness to take the information with the atom "ID" + included in the list of capabilities returned by the CAPABILITY + command. + + Implementations MUST NOT make operational changes based on the data + sent as part of the ID command or response. The ID command is for + human consumption only, and is not to be used in improving the + performance of clients or servers. + + This includes, but is not limited to, the following: + + Servers MUST NOT attempt to work around client bugs by using + information from the ID command. Clients MUST NOT attempt to work + around server bugs based on the ID response. + + Servers MUST NOT provide features to a client or otherwise + optimize for a particular client by using information from the ID + command. Clients MUST NOT provide features to a server or + otherwise optimize for a particular server based on the ID + response. + + Servers MUST NOT deny access to or refuse service for a client + based on information from the ID command. Clients MUST NOT refuse + to operate or limit their operation with a server based on the ID + response. + + + + + + + +Showalter Standards Track [Page 2] + +RFC 2971 IMAP4 ID extension October 2000 + + + Rationale: It is imperative that this extension not supplant IMAP's + CAPABILITY mechanism with a ad-hoc approach where implementations + guess each other's features based on who they claim to be. + + Implementations MUST NOT send false information in an ID command. + + Implementations MAY send less information than they have available or + no information at all. Such behavior may be useful to preserve user + privacy. See Security Considerations, section 7. + +3.1. ID Command + + Arguments: client parameter list or NIL + + Responses: OPTIONAL untagged response: ID + + Result: OK identification information accepted + BAD command unknown or arguments invalid + + Implementation identification information is sent by the client with + the ID command. + + This command is valid in any state. + + The information sent is in the form of a list of field/value pairs. + Fields are permitted to be any IMAP4 string, and values are permitted + to be any IMAP4 string or NIL. A value of NIL indicates that the + client can not or will not specify this information. The client may + also send NIL instead of the list, indicating that it wants to send + no information, but would still accept a server response. + + The available fields are defined in section 3.3. + + Example: C: a023 ID ("name" "sodr" "version" "19.34" "vendor" + "Pink Floyd Music Limited") + S: * ID NIL + S: a023 OK ID completed + +3.2. ID Response + + Contents: server parameter list + + In response to an ID command issued by the client, the server replies + with a tagged response containing information on its implementation. + The format is the same as the client list. + + + + + + +Showalter Standards Track [Page 3] + +RFC 2971 IMAP4 ID extension October 2000 + + + Example: C: a042 ID NIL + S: * ID ("name" "Cyrus" "version" "1.5" "os" "sunos" + "os-version" "5.5" "support-url" + "mailto:cyrus-bugs+@andrew.cmu.edu") + S: a042 OK ID command completed + + A server MUST send a tagged ID response to an ID command. However, a + server MAY send NIL in place of the list. + +3.3. Defined Field Values + + Any string may be sent as a field, but the following are defined to + describe certain values that might be sent. Implementations are free + to send none, any, or all of these. Strings are not case-sensitive. + Field strings MUST NOT be longer than 30 octets. Value strings MUST + NOT be longer than 1024 octets. Implementations MUST NOT send more + than 30 field-value pairs. + + name Name of the program + version Version number of the program + os Name of the operating system + os-version Version of the operating system + vendor Vendor of the client/server + support-url URL to contact for support + address Postal address of contact/vendor + date Date program was released, specified as a date-time + in IMAP4rev1 + command Command used to start the program + arguments Arguments supplied on the command line, if any + if any + environment Description of environment, i.e., UNIX environment + variables or Windows registry settings + + Implementations MUST NOT use contact information to submit automatic + bug reports. Implementations may include information from an ID + response in a report automatically prepared, but are prohibited from + sending the report without user authorization. + + It is preferable to find the name and version of the underlying + operating system at runtime in cases where this is possible. + + Information sent via an ID response may violate user privacy. See + Security Considerations, section 7. + + Implementations MUST NOT send the same field name more than once. + + + + + + +Showalter Standards Track [Page 4] + +RFC 2971 IMAP4 ID extension October 2000 + + +4. Formal Syntax + + This syntax is intended to augment the grammar specified in + [IMAP4rev1] in order to provide for the ID command. This + specification uses the augmented Backus-Naur Form (BNF) notation as + used in [IMAP4rev1]. + + command_any ::= "CAPABILITY" / "LOGOUT" / "NOOP" / x_command / id + ;; adds id command to command_any in [IMAP4rev1] + + id ::= "ID" SPACE id_params_list + + id_response ::= "ID" SPACE id_params_list + + id_params_list ::= "(" #(string SPACE nstring) ")" / nil + ;; list of field value pairs + + response_data ::= "*" SPACE (resp_cond_state / resp_cond_bye / + mailbox_data / message_data / capability_data / id_response) + +5. Use of the ID extension with Firewalls and Other Intermediaries + + There exist proxies, firewalls, and other intermediary systems that + can intercept an IMAP session and make changes to the data exchanged + in the session. Such intermediaries are not anticipated by the IMAP4 + protocol design and are not within the scope of the IMAP4 standard. + However, in order for the ID command to be useful in the presence of + such intermediaries, those intermediaries need to take special note + of the ID command and response. In particular, if an intermediary + changes any part of the IMAP session it must also change the ID + command to advertise its presence. + + A firewall MAY act to block transmission of specific information + fields in the ID command and response that it believes reveal + information that could expose a security vulnerability. However, a + firewall SHOULD NOT disable the extension, when present, entirely, + and SHOULD NOT unconditionally remove either the client or server + list. + + Finally, it should be noted that a firewall, when handling a + CAPABILITY response, MUST NOT allow the names of extensions to be + returned to the client that the firewall has no knowledge of. + + + + + + + + + +Showalter Standards Track [Page 5] + +RFC 2971 IMAP4 ID extension October 2000 + + +6. References + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", RFC 2119, March 1997. + + [IMAP4rev1] Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 2060, October 1996. + + [RFC-822] Crocker, D., "Standard for the Format of ARPA Internet + Text Messages", STD 11, RFC 822, August 1982. + +7. Security Considerations + + This extension has the danger of violating the privacy of users if + misused. Clients and servers should notify users that they implement + and enable the ID command. + + It is highly desirable that implementations provide a method of + disabling ID support, perhaps by not sending ID at all, or by sending + NIL as the argument to the ID command or response. + + Implementors must exercise extreme care in adding fields sent as part + of an ID command or response. Some fields, including a processor ID + number, Ethernet address, or other unique (or mostly unique) + identifier allow tracking of users in ways that violate user privacy + expectations. + + Having implementation information of a given client or server may + make it easier for an attacker to gain unauthorized access due to + security holes. + + Since this command includes arbitrary data and does not require the + user to authenticate, server implementations are cautioned to guard + against an attacker sending arbitrary garbage data in order to fill + up the ID log. In particular, if a server naively logs each ID + command to disk without inspecting it, an attacker can simply fire up + thousands of connections and send a few kilobytes of random data. + Servers have to guard against this. Methods include truncating + abnormally large responses; collating responses by storing only a + single copy, then keeping a counter of the number of times that + response has been seen; keeping only particularly interesting parts + of responses; and only logging responses of users who actually log + in. + + Security is affected by firewalls which modify the IMAP protocol + stream; see section 5, Use of the ID Extension with Firewalls and + Other Intermediaries, for more information. + + + + +Showalter Standards Track [Page 6] + +RFC 2971 IMAP4 ID extension October 2000 + + +8. Author's Address + + Tim Showalter + Mirapoint, Inc. + 909 Hermosa Ct. + Sunnyvale, CA 94095 + + EMail: tjs@mirapoint.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Showalter Standards Track [Page 7] + +RFC 2971 IMAP4 ID extension October 2000 + + +9. Full Copyright Statement + + Copyright (C) The Internet Society (2000). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. + + This document and the information contained herein is provided on an + "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING + TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING + BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION + HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF + MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + + + + + + + + + + + + + +Showalter Standards Track [Page 8] + diff --git a/imap/docs/rfc/rfc3348.txt b/imap/docs/rfc/rfc3348.txt new file mode 100644 index 00000000..500871cc --- /dev/null +++ b/imap/docs/rfc/rfc3348.txt @@ -0,0 +1,339 @@ + + + + + + +Network Working Group M. Gahrns +Request for Comments: 3348 R. Cheng +Category: Informational Microsoft + July 2002 + + + The Internet Message Action Protocol (IMAP4) + Child Mailbox Extension + +Status of this Memo + + This memo provides information for the Internet community. It does + not specify an Internet standard of any kind. Distribution of this + memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2002). All Rights Reserved. + +Abstract + + The Internet Message Action Protocol (IMAP4) CHILDREN extension + provides a mechanism for a client to efficiently determine if a + particular mailbox has children, without issuing a LIST "" * or a + LIST "" % for each mailbox. + +1. Conventions used in this document + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. If such lines are wrapped without a new "C:" or + "S:" label, then the wrapping is for editorial clarity and is not + part of the command. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC-2119]. + +2. Introduction and Overview + + Many IMAP4 [RFC-2060] clients present to the user a hierarchical view + of the mailboxes that a user has access to. Rather than initially + presenting to the user the entire mailbox hierarchy, it is often + preferable to show to the user a collapsed outline list of the + mailbox hierarchy (particularly if there is a large number of + mailboxes). The user can then expand the collapsed outline hierarchy + as needed. It is common to include within the collapsed hierarchy a + + + + + +Gahrns, et al. Informational [Page 1] + +RFC 3348 IMAP4 Child Mailbox Extension July 2002 + + + visual clue (such as a "+") to indicate that there are child + mailboxes under a particular mailbox. When the visual clue is + clicked the hierarchy list is expanded to show the child mailboxes. + + Several IMAP vendors implemented this proposal, and it is proposed to + document this behavior and functionality as an Informational RFC. + + There is interest in addressing the general extensibility of the IMAP + LIST command through an IMAP LIST Extension draft. Similar + functionality to the \HasChildren and \HasNoChildren flags could be + incorporated into this new LIST Extension. It is proposed that the + more general LIST Extension draft proceed on the standards track with + this proposal being relegated to informational status only. + + If the functionality of the \HasChildren and \HasNoChildren flags + were incorporated into a more general LIST extension, this would have + the advantage that a client could then have the opportunity to + request whether or not the server should return this information. + This would be an advantage over the current draft for servers where + this information is expensive to compute, since the server would only + need to compute the information when it knew that the client + requesting the information was able to consume it. + +3. Requirements + + IMAP4 servers that support this extension MUST list the keyword + CHILDREN in their CAPABILITY response. + + The CHILDREN extension defines two new attributes that MAY be + returned within a LIST response. + + \HasChildren - The presence of this attribute indicates that the + mailbox has child mailboxes. + + Servers SHOULD NOT return \HasChildren if child mailboxes exist, but + none will be displayed to the current user in a LIST response (as + should be the case where child mailboxes exist, but a client does not + have permissions to access them.) In this case, \HasNoChildren + SHOULD be used. + + In many cases, however, a server may not be able to efficiently + compute whether a user has access to all child mailboxes, or multiple + users may be accessing the same account and simultaneously changing + the mailbox hierarchy. As such a client MUST be prepared to accept + the \HasChildren attribute as a hint. That is, a mailbox MAY be + flagged with the \HasChildren attribute, but no child mailboxes will + appear in a subsequent LIST response. + + + + +Gahrns, et al. Informational [Page 2] + +RFC 3348 IMAP4 Child Mailbox Extension July 2002 + + + Example 3.1: + ============ + + /*** Consider a server that has the following mailbox hierarchy: + + INBOX + ITEM_1 + ITEM_1A + ITEM_2 + TOP_SECRET + + Where INBOX, ITEM_1 and ITEM_2 are top level mailboxes. ITEM_1A is a + child mailbox of ITEM_1 and TOP_SECRET is a child mailbox of ITEM_2 + that the currently logged on user does NOT have access to. + + Note that in this case, the server is not able to efficiently compute + access rights to child mailboxes and responds with a \HasChildren + attribute for mailbox ITEM_2, even though ITEM_2/TOP_SECRET does not + appear in the list response. ***/ + + C: A001 LIST "" * + S: * LIST (\HasNoChildren) "/" INBOX + S: * LIST (\HasChildren) "/" ITEM_1 + S: * LIST (\HasNoChildren) "/" ITEM_1/ITEM_1A + S: * LIST (\HasChildren) "/" ITEM_2 + S: A001 OK LIST Completed + + \HasNoChildren - The presence of this attribute indicates that the + mailbox has NO child mailboxes that are accessible to the currently + authenticated user. If a mailbox has the \Noinferiors attribute, the + \HasNoChildren attribute is redundant and SHOULD be omitted in the + LIST response. + + In some instances a server that supports the CHILDREN extension MAY + NOT be able to determine whether a mailbox has children. For example + it may have difficulty determining whether there are child mailboxes + when LISTing mailboxes while operating in a particular namespace. + + In these cases, a server MAY exclude both the \HasChildren and + \HasNoChildren attributes in the LIST response. As such, a client + can not make any assumptions about whether a mailbox has children + based upon the absence of a single attribute. + + It is an error for the server to return both a \HasChildren and a + \HasNoChildren attribute in a LIST response. + + + + + + +Gahrns, et al. Informational [Page 3] + +RFC 3348 IMAP4 Child Mailbox Extension July 2002 + + + It is an error for the server to return both a \HasChildren and a + \NoInferiors attribute in a LIST response. + + Note: the \HasNoChildren attribute should not be confused with the + IMAP4 [RFC-2060] defined attribute \Noinferiors which indicates that + no child mailboxes exist now and none can be created in the future. + + The \HasChildren and \HasNoChildren attributes might not be returned + in response to a LSUB response. Many servers maintain a simple + mailbox subscription list that is not updated when the underlying + mailbox structure is changed. A client MUST NOT assume that + hierarchy information will be maintained in the subscription list. + + RLIST is a command defined in [RFC-2193] that includes in a LIST + response mailboxes that are accessible only via referral. That is, a + client must explicitly issue an RLIST command to see a list of these + mailboxes. Thus in the case where a mailbox has child mailboxes that + are available only via referral, the mailboxes would appear as + \HasNoChildren in response to the LIST command, and \HasChildren in + response to the RLIST command. + +5. Formal Syntax + + The following syntax specification uses the augmented Backus-Naur + Form (BNF) as described in [ABNF]. + + Two new mailbox attributes are defined as flag_extensions to the + IMAP4 mailbox_list response: + + HasChildren = "\HasChildren" + + HasNoChildren = "\HasNoChildren" + +6. Security Considerations + + This extension provides a client a more efficient means of + determining whether a particular mailbox has children. If a mailbox + has children, but the currently authenticated user does not have + access to any of them, the server SHOULD respond with a + \HasNoChildren attribute. In many cases, however, a server may not + be able to efficiently compute whether a user has access to all child + mailboxes. If such a server responds with a \HasChildren attribute, + when in fact the currently authenticated user does not have access to + any child mailboxes, potentially more information is conveyed about + the mailbox than intended. A server designed with such levels of + security in mind SHOULD NOT attach the \HasChildren attribute to a + mailbox unless the server is certain that the user has access to at + least one of the child mailboxes. + + + +Gahrns, et al. Informational [Page 4] + +RFC 3348 IMAP4 Child Mailbox Extension July 2002 + + +7. References + + [RFC-2060] Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 2060, December 1996. + + [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC-2234] Crocker, D. and P. Overell, Editors, "Augmented BNF for + Syntax Specifications: ABNF", RFC 2234, November 1997. + + [RFC-2193] Gahrns, M., "IMAP4 Mailbox Referrals", RFC 2193, September + 1997. + +8. Acknowledgments + + The authors would like to thank the participants of several IMC Mail + Connect events for their input when this idea was originally + presented and refined. + +9. Author's Address + + Mike Gahrns + Microsoft + One Microsoft Way + Redmond, WA, 98052 + Phone: (425) 936-9833 + EMail: mikega@microsoft.com + + Raymond Cheng + Microsoft + One Microsoft Way + Redmond, WA, 98052 + Phone: (425) 703-4913 + EMail: raych@microsoft.com + + + + + + + + + + + + + + + + +Gahrns, et al. Informational [Page 5] + +RFC 3348 IMAP4 Child Mailbox Extension July 2002 + + +10. Full Copyright Statement + + Copyright (C) The Internet Society (2002). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. + + This document and the information contained herein is provided on an + "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING + TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING + BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION + HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF + MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + + + + + + + + + + + + + +Gahrns, et al. Informational [Page 6] + diff --git a/imap/docs/rfc/rfc3501.txt b/imap/docs/rfc/rfc3501.txt new file mode 100644 index 00000000..6f470dd1 --- /dev/null +++ b/imap/docs/rfc/rfc3501.txt @@ -0,0 +1,6052 @@ + + + + + + +Network Working Group M. Crispin +Request for Comments: 3501 University of Washington +Obsoletes: 2060 March 2003 +Category: Standards Track + + + INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1 + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2003). All Rights Reserved. + +Abstract + + The Internet Message Access Protocol, Version 4rev1 (IMAP4rev1) + allows a client to access and manipulate electronic mail messages on + a server. IMAP4rev1 permits manipulation of mailboxes (remote + message folders) in a way that is functionally equivalent to local + folders. IMAP4rev1 also provides the capability for an offline + client to resynchronize with the server. + + IMAP4rev1 includes operations for creating, deleting, and renaming + mailboxes, checking for new messages, permanently removing messages, + setting and clearing flags, RFC 2822 and RFC 2045 parsing, searching, + and selective fetching of message attributes, texts, and portions + thereof. Messages in IMAP4rev1 are accessed by the use of numbers. + These numbers are either message sequence numbers or unique + identifiers. + + IMAP4rev1 supports a single server. A mechanism for accessing + configuration information to support multiple IMAP4rev1 servers is + discussed in RFC 2244. + + IMAP4rev1 does not specify a means of posting mail; this function is + handled by a mail transfer protocol such as RFC 2821. + + + + + + + + +Crispin Standards Track [Page 1] + +RFC 3501 IMAPv4 March 2003 + + +Table of Contents + + IMAP4rev1 Protocol Specification ................................ 4 + 1. How to Read This Document ............................... 4 + 1.1. Organization of This Document ........................... 4 + 1.2. Conventions Used in This Document ....................... 4 + 1.3. Special Notes to Implementors ........................... 5 + 2. Protocol Overview ....................................... 6 + 2.1. Link Level .............................................. 6 + 2.2. Commands and Responses .................................. 6 + 2.2.1. Client Protocol Sender and Server Protocol Receiver ..... 6 + 2.2.2. Server Protocol Sender and Client Protocol Receiver ..... 7 + 2.3. Message Attributes ...................................... 8 + 2.3.1. Message Numbers ......................................... 8 + 2.3.1.1. Unique Identifier (UID) Message Attribute ....... 8 + 2.3.1.2. Message Sequence Number Message Attribute ....... 10 + 2.3.2. Flags Message Attribute ................................. 11 + 2.3.3. Internal Date Message Attribute ......................... 12 + 2.3.4. [RFC-2822] Size Message Attribute ....................... 12 + 2.3.5. Envelope Structure Message Attribute .................... 12 + 2.3.6. Body Structure Message Attribute ........................ 12 + 2.4. Message Texts ........................................... 13 + 3. State and Flow Diagram .................................. 13 + 3.1. Not Authenticated State ................................. 13 + 3.2. Authenticated State ..................................... 13 + 3.3. Selected State .......................................... 13 + 3.4. Logout State ............................................ 14 + 4. Data Formats ............................................ 16 + 4.1. Atom .................................................... 16 + 4.2. Number .................................................. 16 + 4.3. String .................................................. 16 + 4.3.1. 8-bit and Binary Strings ................................ 17 + 4.4. Parenthesized List ...................................... 17 + 4.5. NIL ..................................................... 17 + 5. Operational Considerations .............................. 18 + 5.1. Mailbox Naming .......................................... 18 + 5.1.1. Mailbox Hierarchy Naming ................................ 19 + 5.1.2. Mailbox Namespace Naming Convention ..................... 19 + 5.1.3. Mailbox International Naming Convention ................. 19 + 5.2. Mailbox Size and Message Status Updates ................. 21 + 5.3. Response when no Command in Progress .................... 21 + 5.4. Autologout Timer ........................................ 22 + 5.5. Multiple Commands in Progress ........................... 22 + 6. Client Commands ........................................ 23 + 6.1. Client Commands - Any State ............................ 24 + 6.1.1. CAPABILITY Command ..................................... 24 + 6.1.2. NOOP Command ........................................... 25 + 6.1.3. LOGOUT Command ......................................... 26 + + + +Crispin Standards Track [Page 2] + +RFC 3501 IMAPv4 March 2003 + + + 6.2. Client Commands - Not Authenticated State .............. 26 + 6.2.1. STARTTLS Command ....................................... 27 + 6.2.2. AUTHENTICATE Command ................................... 28 + 6.2.3. LOGIN Command .......................................... 30 + 6.3. Client Commands - Authenticated State .................. 31 + 6.3.1. SELECT Command ......................................... 32 + 6.3.2. EXAMINE Command ........................................ 34 + 6.3.3. CREATE Command ......................................... 34 + 6.3.4. DELETE Command ......................................... 35 + 6.3.5. RENAME Command ......................................... 37 + 6.3.6. SUBSCRIBE Command ...................................... 39 + 6.3.7. UNSUBSCRIBE Command .................................... 39 + 6.3.8. LIST Command ........................................... 40 + 6.3.9. LSUB Command ........................................... 43 + 6.3.10. STATUS Command ......................................... 44 + 6.3.11. APPEND Command ......................................... 46 + 6.4. Client Commands - Selected State ....................... 47 + 6.4.1. CHECK Command .......................................... 47 + 6.4.2. CLOSE Command .......................................... 48 + 6.4.3. EXPUNGE Command ........................................ 49 + 6.4.4. SEARCH Command ......................................... 49 + 6.4.5. FETCH Command .......................................... 54 + 6.4.6. STORE Command .......................................... 58 + 6.4.7. COPY Command ........................................... 59 + 6.4.8. UID Command ............................................ 60 + 6.5. Client Commands - Experimental/Expansion ............... 62 + 6.5.1. X<atom> Command ........................................ 62 + 7. Server Responses ....................................... 62 + 7.1. Server Responses - Status Responses .................... 63 + 7.1.1. OK Response ............................................ 65 + 7.1.2. NO Response ............................................ 66 + 7.1.3. BAD Response ........................................... 66 + 7.1.4. PREAUTH Response ....................................... 67 + 7.1.5. BYE Response ........................................... 67 + 7.2. Server Responses - Server and Mailbox Status ........... 68 + 7.2.1. CAPABILITY Response .................................... 68 + 7.2.2. LIST Response .......................................... 69 + 7.2.3. LSUB Response .......................................... 70 + 7.2.4 STATUS Response ........................................ 70 + 7.2.5. SEARCH Response ........................................ 71 + 7.2.6. FLAGS Response ......................................... 71 + 7.3. Server Responses - Mailbox Size ........................ 71 + 7.3.1. EXISTS Response ........................................ 71 + 7.3.2. RECENT Response ........................................ 72 + 7.4. Server Responses - Message Status ...................... 72 + 7.4.1. EXPUNGE Response ....................................... 72 + 7.4.2. FETCH Response ......................................... 73 + 7.5. Server Responses - Command Continuation Request ........ 79 + + + +Crispin Standards Track [Page 3] + +RFC 3501 IMAPv4 March 2003 + + + 8. Sample IMAP4rev1 connection ............................ 80 + 9. Formal Syntax .......................................... 81 + 10. Author's Note .......................................... 92 + 11. Security Considerations ................................ 92 + 11.1. STARTTLS Security Considerations ....................... 92 + 11.2. Other Security Considerations .......................... 93 + 12. IANA Considerations .................................... 94 + Appendices ..................................................... 95 + A. References ............................................. 95 + B. Changes from RFC 2060 .................................. 97 + C. Key Word Index ......................................... 103 + Author's Address ............................................... 107 + Full Copyright Statement ....................................... 108 + +IMAP4rev1 Protocol Specification + +1. How to Read This Document + +1.1. Organization of This Document + + This document is written from the point of view of the implementor of + an IMAP4rev1 client or server. Beyond the protocol overview in + section 2, it is not optimized for someone trying to understand the + operation of the protocol. The material in sections 3 through 5 + provides the general context and definitions with which IMAP4rev1 + operates. + + Sections 6, 7, and 9 describe the IMAP commands, responses, and + syntax, respectively. The relationships among these are such that it + is almost impossible to understand any of them separately. In + particular, do not attempt to deduce command syntax from the command + section alone; instead refer to the Formal Syntax section. + +1.2. Conventions Used in This Document + + "Conventions" are basic principles or procedures. Document + conventions are noted in this section. + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "MAY", and "OPTIONAL" in this document are to + be interpreted as described in [KEYWORDS]. + + The word "can" (not "may") is used to refer to a possible + circumstance or situation, as opposed to an optional facility of the + protocol. + + + +Crispin Standards Track [Page 4] + +RFC 3501 IMAPv4 March 2003 + + + "User" is used to refer to a human user, whereas "client" refers to + the software being run by the user. + + "Connection" refers to the entire sequence of client/server + interaction from the initial establishment of the network connection + until its termination. + + "Session" refers to the sequence of client/server interaction from + the time that a mailbox is selected (SELECT or EXAMINE command) until + the time that selection ends (SELECT or EXAMINE of another mailbox, + CLOSE command, or connection termination). + + Characters are 7-bit US-ASCII unless otherwise specified. Other + character sets are indicated using a "CHARSET", as described in + [MIME-IMT] and defined in [CHARSET]. CHARSETs have important + additional semantics in addition to defining character set; refer to + these documents for more detail. + + There are several protocol conventions in IMAP. These refer to + aspects of the specification which are not strictly part of the IMAP + protocol, but reflect generally-accepted practice. Implementations + need to be aware of these conventions, and avoid conflicts whether or + not they implement the convention. For example, "&" may not be used + as a hierarchy delimiter since it conflicts with the Mailbox + International Naming Convention, and other uses of "&" in mailbox + names are impacted as well. + +1.3. Special Notes to Implementors + + Implementors of the IMAP protocol are strongly encouraged to read the + IMAP implementation recommendations document [IMAP-IMPLEMENTATION] in + conjunction with this document, to help understand the intricacies of + this protocol and how best to build an interoperable product. + + IMAP4rev1 is designed to be upwards compatible from the [IMAP2] and + unpublished IMAP2bis protocols. IMAP4rev1 is largely compatible with + the IMAP4 protocol described in RFC 1730; the exception being in + certain facilities added in RFC 1730 that proved problematic and were + subsequently removed. In the course of the evolution of IMAP4rev1, + some aspects in the earlier protocols have become obsolete. Obsolete + commands, responses, and data formats which an IMAP4rev1 + implementation can encounter when used with an earlier implementation + are described in [IMAP-OBSOLETE]. + + Other compatibility issues with IMAP2bis, the most common variant of + the earlier protocol, are discussed in [IMAP-COMPAT]. A full + discussion of compatibility issues with rare (and presumed extinct) + + + + +Crispin Standards Track [Page 5] + +RFC 3501 IMAPv4 March 2003 + + + variants of [IMAP2] is in [IMAP-HISTORICAL]; this document is + primarily of historical interest. + + IMAP was originally developed for the older [RFC-822] standard, and + as a consequence several fetch items in IMAP incorporate "RFC822" in + their name. With the exception of RFC822.SIZE, there are more modern + replacements; for example, the modern version of RFC822.HEADER is + BODY.PEEK[HEADER]. In all cases, "RFC822" should be interpreted as a + reference to the updated [RFC-2822] standard. + +2. Protocol Overview + +2.1. Link Level + + The IMAP4rev1 protocol assumes a reliable data stream such as that + provided by TCP. When TCP is used, an IMAP4rev1 server listens on + port 143. + +2.2. Commands and Responses + + An IMAP4rev1 connection consists of the establishment of a + client/server network connection, an initial greeting from the + server, and client/server interactions. These client/server + interactions consist of a client command, server data, and a server + completion result response. + + All interactions transmitted by client and server are in the form of + lines, that is, strings that end with a CRLF. The protocol receiver + of an IMAP4rev1 client or server is either reading a line, or is + reading a sequence of octets with a known count followed by a line. + +2.2.1. Client Protocol Sender and Server Protocol Receiver + + The client command begins an operation. Each client command is + prefixed with an identifier (typically a short alphanumeric string, + e.g., A0001, A0002, etc.) called a "tag". A different tag is + generated by the client for each command. + + Clients MUST follow the syntax outlined in this specification + strictly. It is a syntax error to send a command with missing or + extraneous spaces or arguments. + + There are two cases in which a line from the client does not + represent a complete command. In one case, a command argument is + quoted with an octet count (see the description of literal in String + under Data Formats); in the other case, the command arguments require + server feedback (see the AUTHENTICATE command). In either case, the + + + + +Crispin Standards Track [Page 6] + +RFC 3501 IMAPv4 March 2003 + + + server sends a command continuation request response if it is ready + for the octets (if appropriate) and the remainder of the command. + This response is prefixed with the token "+". + + Note: If instead, the server detected an error in the + command, it sends a BAD completion response with a tag + matching the command (as described below) to reject the + command and prevent the client from sending any more of the + command. + + It is also possible for the server to send a completion + response for some other command (if multiple commands are + in progress), or untagged data. In either case, the + command continuation request is still pending; the client + takes the appropriate action for the response, and reads + another response from the server. In all cases, the client + MUST send a complete command (including receiving all + command continuation request responses and command + continuations for the command) before initiating a new + command. + + The protocol receiver of an IMAP4rev1 server reads a command line + from the client, parses the command and its arguments, and transmits + server data and a server command completion result response. + +2.2.2. Server Protocol Sender and Client Protocol Receiver + + Data transmitted by the server to the client and status responses + that do not indicate command completion are prefixed with the token + "*", and are called untagged responses. + + Server data MAY be sent as a result of a client command, or MAY be + sent unilaterally by the server. There is no syntactic difference + between server data that resulted from a specific command and server + data that were sent unilaterally. + + The server completion result response indicates the success or + failure of the operation. It is tagged with the same tag as the + client command which began the operation. Thus, if more than one + command is in progress, the tag in a server completion response + identifies the command to which the response applies. There are + three possible server completion responses: OK (indicating success), + NO (indicating failure), or BAD (indicating a protocol error such as + unrecognized command or command syntax error). + + Servers SHOULD enforce the syntax outlined in this specification + strictly. Any client command with a protocol syntax error, including + (but not limited to) missing or extraneous spaces or arguments, + + + +Crispin Standards Track [Page 7] + +RFC 3501 IMAPv4 March 2003 + + + SHOULD be rejected, and the client given a BAD server completion + response. + + The protocol receiver of an IMAP4rev1 client reads a response line + from the server. It then takes action on the response based upon the + first token of the response, which can be a tag, a "*", or a "+". + + A client MUST be prepared to accept any server response at all times. + This includes server data that was not requested. Server data SHOULD + be recorded, so that the client can reference its recorded copy + rather than sending a command to the server to request the data. In + the case of certain server data, the data MUST be recorded. + + This topic is discussed in greater detail in the Server Responses + section. + +2.3. Message Attributes + + In addition to message text, each message has several attributes + associated with it. These attributes can be retrieved individually + or in conjunction with other attributes or message texts. + +2.3.1. Message Numbers + + Messages in IMAP4rev1 are accessed by one of two numbers; the unique + identifier or the message sequence number. + + +2.3.1.1. Unique Identifier (UID) Message Attribute + + A 32-bit value assigned to each message, which when used with the + unique identifier validity value (see below) forms a 64-bit value + that MUST NOT refer to any other message in the mailbox or any + subsequent mailbox with the same name forever. Unique identifiers + are assigned in a strictly ascending fashion in the mailbox; as each + message is added to the mailbox it is assigned a higher UID than the + message(s) which were added previously. Unlike message sequence + numbers, unique identifiers are not necessarily contiguous. + + The unique identifier of a message MUST NOT change during the + session, and SHOULD NOT change between sessions. Any change of + unique identifiers between sessions MUST be detectable using the + UIDVALIDITY mechanism discussed below. Persistent unique identifiers + are required for a client to resynchronize its state from a previous + session with the server (e.g., disconnected or offline access + clients); this is discussed further in [IMAP-DISC]. + + + + + +Crispin Standards Track [Page 8] + +RFC 3501 IMAPv4 March 2003 + + + Associated with every mailbox are two values which aid in unique + identifier handling: the next unique identifier value and the unique + identifier validity value. + + The next unique identifier value is the predicted value that will be + assigned to a new message in the mailbox. Unless the unique + identifier validity also changes (see below), the next unique + identifier value MUST have the following two characteristics. First, + the next unique identifier value MUST NOT change unless new messages + are added to the mailbox; and second, the next unique identifier + value MUST change whenever new messages are added to the mailbox, + even if those new messages are subsequently expunged. + + Note: The next unique identifier value is intended to + provide a means for a client to determine whether any + messages have been delivered to the mailbox since the + previous time it checked this value. It is not intended to + provide any guarantee that any message will have this + unique identifier. A client can only assume, at the time + that it obtains the next unique identifier value, that + messages arriving after that time will have a UID greater + than or equal to that value. + + The unique identifier validity value is sent in a UIDVALIDITY + response code in an OK untagged response at mailbox selection time. + If unique identifiers from an earlier session fail to persist in this + session, the unique identifier validity value MUST be greater than + the one used in the earlier session. + + Note: Ideally, unique identifiers SHOULD persist at all + times. Although this specification recognizes that failure + to persist can be unavoidable in certain server + environments, it STRONGLY ENCOURAGES message store + implementation techniques that avoid this problem. For + example: + + 1) Unique identifiers MUST be strictly ascending in the + mailbox at all times. If the physical message store is + re-ordered by a non-IMAP agent, this requires that the + unique identifiers in the mailbox be regenerated, since + the former unique identifiers are no longer strictly + ascending as a result of the re-ordering. + + 2) If the message store has no mechanism to store unique + identifiers, it must regenerate unique identifiers at + each session, and each session must have a unique + UIDVALIDITY value. + + + + +Crispin Standards Track [Page 9] + +RFC 3501 IMAPv4 March 2003 + + + 3) If the mailbox is deleted and a new mailbox with the + same name is created at a later date, the server must + either keep track of unique identifiers from the + previous instance of the mailbox, or it must assign a + new UIDVALIDITY value to the new instance of the + mailbox. A good UIDVALIDITY value to use in this case + is a 32-bit representation of the creation date/time of + the mailbox. It is alright to use a constant such as + 1, but only if it guaranteed that unique identifiers + will never be reused, even in the case of a mailbox + being deleted (or renamed) and a new mailbox by the + same name created at some future time. + + 4) The combination of mailbox name, UIDVALIDITY, and UID + must refer to a single immutable message on that server + forever. In particular, the internal date, [RFC-2822] + size, envelope, body structure, and message texts + (RFC822, RFC822.HEADER, RFC822.TEXT, and all BODY[...] + fetch data items) must never change. This does not + include message numbers, nor does it include attributes + that can be set by a STORE command (e.g., FLAGS). + + +2.3.1.2. Message Sequence Number Message Attribute + + A relative position from 1 to the number of messages in the mailbox. + This position MUST be ordered by ascending unique identifier. As + each new message is added, it is assigned a message sequence number + that is 1 higher than the number of messages in the mailbox before + that new message was added. + + Message sequence numbers can be reassigned during the session. For + example, when a message is permanently removed (expunged) from the + mailbox, the message sequence number for all subsequent messages is + decremented. The number of messages in the mailbox is also + decremented. Similarly, a new message can be assigned a message + sequence number that was once held by some other message prior to an + expunge. + + In addition to accessing messages by relative position in the + mailbox, message sequence numbers can be used in mathematical + calculations. For example, if an untagged "11 EXISTS" is received, + and previously an untagged "8 EXISTS" was received, three new + messages have arrived with message sequence numbers of 9, 10, and 11. + Another example, if message 287 in a 523 message mailbox has UID + 12345, there are exactly 286 messages which have lesser UIDs and 236 + messages which have greater UIDs. + + + + +Crispin Standards Track [Page 10] + +RFC 3501 IMAPv4 March 2003 + + +2.3.2. Flags Message Attribute + + A list of zero or more named tokens associated with the message. A + flag is set by its addition to this list, and is cleared by its + removal. There are two types of flags in IMAP4rev1. A flag of + either type can be permanent or session-only. + + A system flag is a flag name that is pre-defined in this + specification. All system flags begin with "\". Certain system + flags (\Deleted and \Seen) have special semantics described + elsewhere. The currently-defined system flags are: + + \Seen + Message has been read + + \Answered + Message has been answered + + \Flagged + Message is "flagged" for urgent/special attention + + \Deleted + Message is "deleted" for removal by later EXPUNGE + + \Draft + Message has not completed composition (marked as a draft). + + \Recent + Message is "recently" arrived in this mailbox. This session + is the first session to have been notified about this + message; if the session is read-write, subsequent sessions + will not see \Recent set for this message. This flag can not + be altered by the client. + + If it is not possible to determine whether or not this + session is the first session to be notified about a message, + then that message SHOULD be considered recent. + + If multiple connections have the same mailbox selected + simultaneously, it is undefined which of these connections + will see newly-arrived messages with \Recent set and which + will see it without \Recent set. + + A keyword is defined by the server implementation. Keywords do not + begin with "\". Servers MAY permit the client to define new keywords + in the mailbox (see the description of the PERMANENTFLAGS response + code for more information). + + + + +Crispin Standards Track [Page 11] + +RFC 3501 IMAPv4 March 2003 + + + A flag can be permanent or session-only on a per-flag basis. + Permanent flags are those which the client can add or remove from the + message flags permanently; that is, concurrent and subsequent + sessions will see any change in permanent flags. Changes to session + flags are valid only in that session. + + Note: The \Recent system flag is a special case of a + session flag. \Recent can not be used as an argument in a + STORE or APPEND command, and thus can not be changed at + all. + +2.3.3. Internal Date Message Attribute + + The internal date and time of the message on the server. This + is not the date and time in the [RFC-2822] header, but rather a + date and time which reflects when the message was received. In + the case of messages delivered via [SMTP], this SHOULD be the + date and time of final delivery of the message as defined by + [SMTP]. In the case of messages delivered by the IMAP4rev1 COPY + command, this SHOULD be the internal date and time of the source + message. In the case of messages delivered by the IMAP4rev1 + APPEND command, this SHOULD be the date and time as specified in + the APPEND command description. All other cases are + implementation defined. + +2.3.4. [RFC-2822] Size Message Attribute + + The number of octets in the message, as expressed in [RFC-2822] + format. + +2.3.5. Envelope Structure Message Attribute + + A parsed representation of the [RFC-2822] header of the message. + Note that the IMAP Envelope structure is not the same as an + [SMTP] envelope. + +2.3.6. Body Structure Message Attribute + + A parsed representation of the [MIME-IMB] body structure + information of the message. + + + + + + + + + + + +Crispin Standards Track [Page 12] + +RFC 3501 IMAPv4 March 2003 + + +2.4. Message Texts + + In addition to being able to fetch the full [RFC-2822] text of a + message, IMAP4rev1 permits the fetching of portions of the full + message text. Specifically, it is possible to fetch the + [RFC-2822] message header, [RFC-2822] message body, a [MIME-IMB] + body part, or a [MIME-IMB] header. + +3. State and Flow Diagram + + Once the connection between client and server is established, an + IMAP4rev1 connection is in one of four states. The initial + state is identified in the server greeting. Most commands are + only valid in certain states. It is a protocol error for the + client to attempt a command while the connection is in an + inappropriate state, and the server will respond with a BAD or + NO (depending upon server implementation) command completion + result. + +3.1. Not Authenticated State + + In the not authenticated state, the client MUST supply + authentication credentials before most commands will be + permitted. This state is entered when a connection starts + unless the connection has been pre-authenticated. + +3.2. Authenticated State + + In the authenticated state, the client is authenticated and MUST + select a mailbox to access before commands that affect messages + will be permitted. This state is entered when a + pre-authenticated connection starts, when acceptable + authentication credentials have been provided, after an error in + selecting a mailbox, or after a successful CLOSE command. + +3.3. Selected State + + In a selected state, a mailbox has been selected to access. + This state is entered when a mailbox has been successfully + selected. + + + + + + + + + + + +Crispin Standards Track [Page 13] + +RFC 3501 IMAPv4 March 2003 + + +3.4. Logout State + + In the logout state, the connection is being terminated. This + state can be entered as a result of a client request (via the + LOGOUT command) or by unilateral action on the part of either + the client or server. + + If the client requests the logout state, the server MUST send an + untagged BYE response and a tagged OK response to the LOGOUT + command before the server closes the connection; and the client + MUST read the tagged OK response to the LOGOUT command before + the client closes the connection. + + A server MUST NOT unilaterally close the connection without + sending an untagged BYE response that contains the reason for + having done so. A client SHOULD NOT unilaterally close the + connection, and instead SHOULD issue a LOGOUT command. If the + server detects that the client has unilaterally closed the + connection, the server MAY omit the untagged BYE response and + simply close its connection. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Crispin Standards Track [Page 14] + +RFC 3501 IMAPv4 March 2003 + + + +----------------------+ + |connection established| + +----------------------+ + || + \/ + +--------------------------------------+ + | server greeting | + +--------------------------------------+ + || (1) || (2) || (3) + \/ || || + +-----------------+ || || + |Not Authenticated| || || + +-----------------+ || || + || (7) || (4) || || + || \/ \/ || + || +----------------+ || + || | Authenticated |<=++ || + || +----------------+ || || + || || (7) || (5) || (6) || + || || \/ || || + || || +--------+ || || + || || |Selected|==++ || + || || +--------+ || + || || || (7) || + \/ \/ \/ \/ + +--------------------------------------+ + | Logout | + +--------------------------------------+ + || + \/ + +-------------------------------+ + |both sides close the connection| + +-------------------------------+ + + (1) connection without pre-authentication (OK greeting) + (2) pre-authenticated connection (PREAUTH greeting) + (3) rejected connection (BYE greeting) + (4) successful LOGIN or AUTHENTICATE command + (5) successful SELECT or EXAMINE command + (6) CLOSE command, or failed SELECT or EXAMINE command + (7) LOGOUT command, server shutdown, or connection closed + + + + + + + + + + +Crispin Standards Track [Page 15] + +RFC 3501 IMAPv4 March 2003 + + +4. Data Formats + + IMAP4rev1 uses textual commands and responses. Data in + IMAP4rev1 can be in one of several forms: atom, number, string, + parenthesized list, or NIL. Note that a particular data item + may take more than one form; for example, a data item defined as + using "astring" syntax may be either an atom or a string. + +4.1. Atom + + An atom consists of one or more non-special characters. + +4.2. Number + + A number consists of one or more digit characters, and + represents a numeric value. + +4.3. String + + A string is in one of two forms: either literal or quoted + string. The literal form is the general form of string. The + quoted string form is an alternative that avoids the overhead of + processing a literal at the cost of limitations of characters + which may be used. + + A literal is a sequence of zero or more octets (including CR and + LF), prefix-quoted with an octet count in the form of an open + brace ("{"), the number of octets, close brace ("}"), and CRLF. + In the case of literals transmitted from server to client, the + CRLF is immediately followed by the octet data. In the case of + literals transmitted from client to server, the client MUST wait + to receive a command continuation request (described later in + this document) before sending the octet data (and the remainder + of the command). + + A quoted string is a sequence of zero or more 7-bit characters, + excluding CR and LF, with double quote (<">) characters at each + end. + + The empty string is represented as either "" (a quoted string + with zero characters between double quotes) or as {0} followed + by CRLF (a literal with an octet count of 0). + + Note: Even if the octet count is 0, a client transmitting a + literal MUST wait to receive a command continuation request. + + + + + + +Crispin Standards Track [Page 16] + +RFC 3501 IMAPv4 March 2003 + + +4.3.1. 8-bit and Binary Strings + + 8-bit textual and binary mail is supported through the use of a + [MIME-IMB] content transfer encoding. IMAP4rev1 implementations MAY + transmit 8-bit or multi-octet characters in literals, but SHOULD do + so only when the [CHARSET] is identified. + + Although a BINARY body encoding is defined, unencoded binary strings + are not permitted. A "binary string" is any string with NUL + characters. Implementations MUST encode binary data into a textual + form, such as BASE64, before transmitting the data. A string with an + excessive amount of CTL characters MAY also be considered to be + binary. + +4.4. Parenthesized List + + Data structures are represented as a "parenthesized list"; a sequence + of data items, delimited by space, and bounded at each end by + parentheses. A parenthesized list can contain other parenthesized + lists, using multiple levels of parentheses to indicate nesting. + + The empty list is represented as () -- a parenthesized list with no + members. + +4.5. NIL + + The special form "NIL" represents the non-existence of a particular + data item that is represented as a string or parenthesized list, as + distinct from the empty string "" or the empty parenthesized list (). + + Note: NIL is never used for any data item which takes the + form of an atom. For example, a mailbox name of "NIL" is a + mailbox named NIL as opposed to a non-existent mailbox + name. This is because mailbox uses "astring" syntax which + is an atom or a string. Conversely, an addr-name of NIL is + a non-existent personal name, because addr-name uses + "nstring" syntax which is NIL or a string, but never an + atom. + + + + + + + + + + + + + +Crispin Standards Track [Page 17] + +RFC 3501 IMAPv4 March 2003 + + +5. Operational Considerations + + The following rules are listed here to ensure that all IMAP4rev1 + implementations interoperate properly. + +5.1. Mailbox Naming + + Mailbox names are 7-bit. Client implementations MUST NOT attempt to + create 8-bit mailbox names, and SHOULD interpret any 8-bit mailbox + names returned by LIST or LSUB as UTF-8. Server implementations + SHOULD prohibit the creation of 8-bit mailbox names, and SHOULD NOT + return 8-bit mailbox names in LIST or LSUB. See section 5.1.3 for + more information on how to represent non-ASCII mailbox names. + + Note: 8-bit mailbox names were undefined in earlier + versions of this protocol. Some sites used a local 8-bit + character set to represent non-ASCII mailbox names. Such + usage is not interoperable, and is now formally deprecated. + + The case-insensitive mailbox name INBOX is a special name reserved to + mean "the primary mailbox for this user on this server". The + interpretation of all other names is implementation-dependent. + + In particular, this specification takes no position on case + sensitivity in non-INBOX mailbox names. Some server implementations + are fully case-sensitive; others preserve case of a newly-created + name but otherwise are case-insensitive; and yet others coerce names + to a particular case. Client implementations MUST interact with any + of these. If a server implementation interprets non-INBOX mailbox + names as case-insensitive, it MUST treat names using the + international naming convention specially as described in section + 5.1.3. + + There are certain client considerations when creating a new mailbox + name: + + 1) Any character which is one of the atom-specials (see the Formal + Syntax) will require that the mailbox name be represented as a + quoted string or literal. + + 2) CTL and other non-graphic characters are difficult to represent + in a user interface and are best avoided. + + 3) Although the list-wildcard characters ("%" and "*") are valid + in a mailbox name, it is difficult to use such mailbox names + with the LIST and LSUB commands due to the conflict with + wildcard interpretation. + + + + +Crispin Standards Track [Page 18] + +RFC 3501 IMAPv4 March 2003 + + + 4) Usually, a character (determined by the server implementation) + is reserved to delimit levels of hierarchy. + + 5) Two characters, "#" and "&", have meanings by convention, and + should be avoided except when used in that convention. + +5.1.1. Mailbox Hierarchy Naming + + If it is desired to export hierarchical mailbox names, mailbox names + MUST be left-to-right hierarchical using a single character to + separate levels of hierarchy. The same hierarchy separator character + is used for all levels of hierarchy within a single name. + +5.1.2. Mailbox Namespace Naming Convention + + By convention, the first hierarchical element of any mailbox name + which begins with "#" identifies the "namespace" of the remainder of + the name. This makes it possible to disambiguate between different + types of mailbox stores, each of which have their own namespaces. + + For example, implementations which offer access to USENET + newsgroups MAY use the "#news" namespace to partition the + USENET newsgroup namespace from that of other mailboxes. + Thus, the comp.mail.misc newsgroup would have a mailbox + name of "#news.comp.mail.misc", and the name + "comp.mail.misc" can refer to a different object (e.g., a + user's private mailbox). + +5.1.3. Mailbox International Naming Convention + + By convention, international mailbox names in IMAP4rev1 are specified + using a modified version of the UTF-7 encoding described in [UTF-7]. + Modified UTF-7 may also be usable in servers that implement an + earlier version of this protocol. + + In modified UTF-7, printable US-ASCII characters, except for "&", + represent themselves; that is, characters with octet values 0x20-0x25 + and 0x27-0x7e. The character "&" (0x26) is represented by the + two-octet sequence "&-". + + All other characters (octet values 0x00-0x1f and 0x7f-0xff) are + represented in modified BASE64, with a further modification from + [UTF-7] that "," is used instead of "/". Modified BASE64 MUST NOT be + used to represent any printing US-ASCII character which can represent + itself. + + + + + + +Crispin Standards Track [Page 19] + +RFC 3501 IMAPv4 March 2003 + + + "&" is used to shift to modified BASE64 and "-" to shift back to + US-ASCII. There is no implicit shift from BASE64 to US-ASCII, and + null shifts ("-&" while in BASE64; note that "&-" while in US-ASCII + means "&") are not permitted. However, all names start in US-ASCII, + and MUST end in US-ASCII; that is, a name that ends with a non-ASCII + ISO-10646 character MUST end with a "-"). + + The purpose of these modifications is to correct the following + problems with UTF-7: + + 1) UTF-7 uses the "+" character for shifting; this conflicts with + the common use of "+" in mailbox names, in particular USENET + newsgroup names. + + 2) UTF-7's encoding is BASE64 which uses the "/" character; this + conflicts with the use of "/" as a popular hierarchy delimiter. + + 3) UTF-7 prohibits the unencoded usage of "\"; this conflicts with + the use of "\" as a popular hierarchy delimiter. + + 4) UTF-7 prohibits the unencoded usage of "~"; this conflicts with + the use of "~" in some servers as a home directory indicator. + + 5) UTF-7 permits multiple alternate forms to represent the same + string; in particular, printable US-ASCII characters can be + represented in encoded form. + + Although modified UTF-7 is a convention, it establishes certain + requirements on server handling of any mailbox name with an + embedded "&" character. In particular, server implementations + MUST preserve the exact form of the modified BASE64 portion of a + modified UTF-7 name and treat that text as case-sensitive, even if + names are otherwise case-insensitive or case-folded. + + Server implementations SHOULD verify that any mailbox name with an + embedded "&" character, used as an argument to CREATE, is: in the + correctly modified UTF-7 syntax, has no superfluous shifts, and + has no encoding in modified BASE64 of any printing US-ASCII + character which can represent itself. However, client + implementations MUST NOT depend upon the server doing this, and + SHOULD NOT attempt to create a mailbox name with an embedded "&" + character unless it complies with the modified UTF-7 syntax. + + Server implementations which export a mail store that does not + follow the modified UTF-7 convention MUST convert to modified + UTF-7 any mailbox name that contains either non-ASCII characters + or the "&" character. + + + + +Crispin Standards Track [Page 20] + +RFC 3501 IMAPv4 March 2003 + + + For example, here is a mailbox name which mixes English, + Chinese, and Japanese text: + ~peter/mail/&U,BTFw-/&ZeVnLIqe- + + For example, the string "&Jjo!" is not a valid mailbox + name because it does not contain a shift to US-ASCII + before the "!". The correct form is "&Jjo-!". The + string "&U,BTFw-&ZeVnLIqe-" is not permitted because it + contains a superfluous shift. The correct form is + "&U,BTF2XlZyyKng-". + +5.2. Mailbox Size and Message Status Updates + + At any time, a server can send data that the client did not request. + Sometimes, such behavior is REQUIRED. For example, agents other than + the server MAY add messages to the mailbox (e.g., new message + delivery), change the flags of the messages in the mailbox (e.g., + simultaneous access to the same mailbox by multiple agents), or even + remove messages from the mailbox. A server MUST send mailbox size + updates automatically if a mailbox size change is observed during the + processing of a command. A server SHOULD send message flag updates + automatically, without requiring the client to request such updates + explicitly. + + Special rules exist for server notification of a client about the + removal of messages to prevent synchronization errors; see the + description of the EXPUNGE response for more detail. In particular, + it is NOT permitted to send an EXISTS response that would reduce the + number of messages in the mailbox; only the EXPUNGE response can do + this. + + Regardless of what implementation decisions a client makes on + remembering data from the server, a client implementation MUST record + mailbox size updates. It MUST NOT assume that any command after the + initial mailbox selection will return the size of the mailbox. + +5.3. Response when no Command in Progress + + Server implementations are permitted to send an untagged response + (except for EXPUNGE) while there is no command in progress. Server + implementations that send such responses MUST deal with flow control + considerations. Specifically, they MUST either (1) verify that the + size of the data does not exceed the underlying transport's available + window size, or (2) use non-blocking writes. + + + + + + + +Crispin Standards Track [Page 21] + +RFC 3501 IMAPv4 March 2003 + + +5.4. Autologout Timer + + If a server has an inactivity autologout timer, the duration of that + timer MUST be at least 30 minutes. The receipt of ANY command from + the client during that interval SHOULD suffice to reset the + autologout timer. + +5.5. Multiple Commands in Progress + + The client MAY send another command without waiting for the + completion result response of a command, subject to ambiguity rules + (see below) and flow control constraints on the underlying data + stream. Similarly, a server MAY begin processing another command + before processing the current command to completion, subject to + ambiguity rules. However, any command continuation request responses + and command continuations MUST be negotiated before any subsequent + command is initiated. + + The exception is if an ambiguity would result because of a command + that would affect the results of other commands. Clients MUST NOT + send multiple commands without waiting if an ambiguity would result. + If the server detects a possible ambiguity, it MUST execute commands + to completion in the order given by the client. + + The most obvious example of ambiguity is when a command would affect + the results of another command, e.g., a FETCH of a message's flags + and a STORE of that same message's flags. + + A non-obvious ambiguity occurs with commands that permit an untagged + EXPUNGE response (commands other than FETCH, STORE, and SEARCH), + since an untagged EXPUNGE response can invalidate sequence numbers in + a subsequent command. This is not a problem for FETCH, STORE, or + SEARCH commands because servers are prohibited from sending EXPUNGE + responses while any of those commands are in progress. Therefore, if + the client sends any command other than FETCH, STORE, or SEARCH, it + MUST wait for the completion result response before sending a command + with message sequence numbers. + + Note: UID FETCH, UID STORE, and UID SEARCH are different + commands from FETCH, STORE, and SEARCH. If the client + sends a UID command, it must wait for a completion result + response before sending a command with message sequence + numbers. + + + + + + + + +Crispin Standards Track [Page 22] + +RFC 3501 IMAPv4 March 2003 + + + For example, the following non-waiting command sequences are invalid: + + FETCH + NOOP + STORE + STORE + COPY + FETCH + COPY + COPY + CHECK + FETCH + + The following are examples of valid non-waiting command sequences: + + FETCH + STORE + SEARCH + CHECK + STORE + COPY + EXPUNGE + + UID SEARCH + UID SEARCH may be valid or invalid as a non-waiting + command sequence, depending upon whether or not the second UID + SEARCH contains message sequence numbers. + +6. Client Commands + + IMAP4rev1 commands are described in this section. Commands are + organized by the state in which the command is permitted. Commands + which are permitted in multiple states are listed in the minimum + permitted state (for example, commands valid in authenticated and + selected state are listed in the authenticated state commands). + + Command arguments, identified by "Arguments:" in the command + descriptions below, are described by function, not by syntax. The + precise syntax of command arguments is described in the Formal Syntax + section. + + Some commands cause specific server responses to be returned; these + are identified by "Responses:" in the command descriptions below. + See the response descriptions in the Responses section for + information on these responses, and the Formal Syntax section for the + precise syntax of these responses. It is possible for server data to + be transmitted as a result of any command. Thus, commands that do + not specifically require server data specify "no specific responses + for this command" instead of "none". + + The "Result:" in the command description refers to the possible + tagged status responses to a command, and any special interpretation + of these status responses. + + The state of a connection is only changed by successful commands + which are documented as changing state. A rejected command (BAD + response) never changes the state of the connection or of the + selected mailbox. A failed command (NO response) generally does not + change the state of the connection or of the selected mailbox; the + exception being the SELECT and EXAMINE commands. + + + +Crispin Standards Track [Page 23] + +RFC 3501 IMAPv4 March 2003 + + +6.1. Client Commands - Any State + + The following commands are valid in any state: CAPABILITY, NOOP, and + LOGOUT. + +6.1.1. CAPABILITY Command + + Arguments: none + + Responses: REQUIRED untagged response: CAPABILITY + + Result: OK - capability completed + BAD - command unknown or arguments invalid + + The CAPABILITY command requests a listing of capabilities that the + server supports. The server MUST send a single untagged + CAPABILITY response with "IMAP4rev1" as one of the listed + capabilities before the (tagged) OK response. + + A capability name which begins with "AUTH=" indicates that the + server supports that particular authentication mechanism. All + such names are, by definition, part of this specification. For + example, the authorization capability for an experimental + "blurdybloop" authenticator would be "AUTH=XBLURDYBLOOP" and not + "XAUTH=BLURDYBLOOP" or "XAUTH=XBLURDYBLOOP". + + Other capability names refer to extensions, revisions, or + amendments to this specification. See the documentation of the + CAPABILITY response for additional information. No capabilities, + beyond the base IMAP4rev1 set defined in this specification, are + enabled without explicit client action to invoke the capability. + + Client and server implementations MUST implement the STARTTLS, + LOGINDISABLED, and AUTH=PLAIN (described in [IMAP-TLS]) + capabilities. See the Security Considerations section for + important information. + + See the section entitled "Client Commands - + Experimental/Expansion" for information about the form of site or + implementation-specific capabilities. + + + + + + + + + + + +Crispin Standards Track [Page 24] + +RFC 3501 IMAPv4 March 2003 + + + Example: C: abcd CAPABILITY + S: * CAPABILITY IMAP4rev1 STARTTLS AUTH=GSSAPI + LOGINDISABLED + S: abcd OK CAPABILITY completed + C: efgh STARTTLS + S: efgh OK STARTLS completed + <TLS negotiation, further commands are under [TLS] layer> + C: ijkl CAPABILITY + S: * CAPABILITY IMAP4rev1 AUTH=GSSAPI AUTH=PLAIN + S: ijkl OK CAPABILITY completed + + +6.1.2. NOOP Command + + Arguments: none + + Responses: no specific responses for this command (but see below) + + Result: OK - noop completed + BAD - command unknown or arguments invalid + + The NOOP command always succeeds. It does nothing. + + Since any command can return a status update as untagged data, the + NOOP command can be used as a periodic poll for new messages or + message status updates during a period of inactivity (this is the + preferred method to do this). The NOOP command can also be used + to reset any inactivity autologout timer on the server. + + Example: C: a002 NOOP + S: a002 OK NOOP completed + . . . + C: a047 NOOP + S: * 22 EXPUNGE + S: * 23 EXISTS + S: * 3 RECENT + S: * 14 FETCH (FLAGS (\Seen \Deleted)) + S: a047 OK NOOP completed + + + + + + + + + + + + + +Crispin Standards Track [Page 25] + +RFC 3501 IMAPv4 March 2003 + + +6.1.3. LOGOUT Command + + Arguments: none + + Responses: REQUIRED untagged response: BYE + + Result: OK - logout completed + BAD - command unknown or arguments invalid + + The LOGOUT command informs the server that the client is done with + the connection. The server MUST send a BYE untagged response + before the (tagged) OK response, and then close the network + connection. + + Example: C: A023 LOGOUT + S: * BYE IMAP4rev1 Server logging out + S: A023 OK LOGOUT completed + (Server and client then close the connection) + +6.2. Client Commands - Not Authenticated State + + In the not authenticated state, the AUTHENTICATE or LOGIN command + establishes authentication and enters the authenticated state. The + AUTHENTICATE command provides a general mechanism for a variety of + authentication techniques, privacy protection, and integrity + checking; whereas the LOGIN command uses a traditional user name and + plaintext password pair and has no means of establishing privacy + protection or integrity checking. + + The STARTTLS command is an alternate form of establishing session + privacy protection and integrity checking, but does not establish + authentication or enter the authenticated state. + + Server implementations MAY allow access to certain mailboxes without + establishing authentication. This can be done by means of the + ANONYMOUS [SASL] authenticator described in [ANONYMOUS]. An older + convention is a LOGIN command using the userid "anonymous"; in this + case, a password is required although the server may choose to accept + any password. The restrictions placed on anonymous users are + implementation-dependent. + + Once authenticated (including as anonymous), it is not possible to + re-enter not authenticated state. + + + + + + + + +Crispin Standards Track [Page 26] + +RFC 3501 IMAPv4 March 2003 + + + In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT), + the following commands are valid in the not authenticated state: + STARTTLS, AUTHENTICATE and LOGIN. See the Security Considerations + section for important information about these commands. + +6.2.1. STARTTLS Command + + Arguments: none + + Responses: no specific response for this command + + Result: OK - starttls completed, begin TLS negotiation + BAD - command unknown or arguments invalid + + A [TLS] negotiation begins immediately after the CRLF at the end + of the tagged OK response from the server. Once a client issues a + STARTTLS command, it MUST NOT issue further commands until a + server response is seen and the [TLS] negotiation is complete. + + The server remains in the non-authenticated state, even if client + credentials are supplied during the [TLS] negotiation. This does + not preclude an authentication mechanism such as EXTERNAL (defined + in [SASL]) from using client identity determined by the [TLS] + negotiation. + + Once [TLS] has been started, the client MUST discard cached + information about server capabilities and SHOULD re-issue the + CAPABILITY command. This is necessary to protect against man-in- + the-middle attacks which alter the capabilities list prior to + STARTTLS. The server MAY advertise different capabilities after + STARTTLS. + + Example: C: a001 CAPABILITY + S: * CAPABILITY IMAP4rev1 STARTTLS LOGINDISABLED + S: a001 OK CAPABILITY completed + C: a002 STARTTLS + S: a002 OK Begin TLS negotiation now + <TLS negotiation, further commands are under [TLS] layer> + C: a003 CAPABILITY + S: * CAPABILITY IMAP4rev1 AUTH=PLAIN + S: a003 OK CAPABILITY completed + C: a004 LOGIN joe password + S: a004 OK LOGIN completed + + + + + + + + +Crispin Standards Track [Page 27] + +RFC 3501 IMAPv4 March 2003 + + +6.2.2. AUTHENTICATE Command + + Arguments: authentication mechanism name + + Responses: continuation data can be requested + + Result: OK - authenticate completed, now in authenticated state + NO - authenticate failure: unsupported authentication + mechanism, credentials rejected + BAD - command unknown or arguments invalid, + authentication exchange cancelled + + The AUTHENTICATE command indicates a [SASL] authentication + mechanism to the server. If the server supports the requested + authentication mechanism, it performs an authentication protocol + exchange to authenticate and identify the client. It MAY also + negotiate an OPTIONAL security layer for subsequent protocol + interactions. If the requested authentication mechanism is not + supported, the server SHOULD reject the AUTHENTICATE command by + sending a tagged NO response. + + The AUTHENTICATE command does not support the optional "initial + response" feature of [SASL]. Section 5.1 of [SASL] specifies how + to handle an authentication mechanism which uses an initial + response. + + The service name specified by this protocol's profile of [SASL] is + "imap". + + The authentication protocol exchange consists of a series of + server challenges and client responses that are specific to the + authentication mechanism. A server challenge consists of a + command continuation request response with the "+" token followed + by a BASE64 encoded string. The client response consists of a + single line consisting of a BASE64 encoded string. If the client + wishes to cancel an authentication exchange, it issues a line + consisting of a single "*". If the server receives such a + response, it MUST reject the AUTHENTICATE command by sending a + tagged BAD response. + + If a security layer is negotiated through the [SASL] + authentication exchange, it takes effect immediately following the + CRLF that concludes the authentication exchange for the client, + and the CRLF of the tagged OK response for the server. + + While client and server implementations MUST implement the + AUTHENTICATE command itself, it is not required to implement any + authentication mechanisms other than the PLAIN mechanism described + + + +Crispin Standards Track [Page 28] + +RFC 3501 IMAPv4 March 2003 + + + in [IMAP-TLS]. Also, an authentication mechanism is not required + to support any security layers. + + Note: a server implementation MUST implement a + configuration in which it does NOT permit any plaintext + password mechanisms, unless either the STARTTLS command + has been negotiated or some other mechanism that + protects the session from password snooping has been + provided. Server sites SHOULD NOT use any configuration + which permits a plaintext password mechanism without + such a protection mechanism against password snooping. + Client and server implementations SHOULD implement + additional [SASL] mechanisms that do not use plaintext + passwords, such the GSSAPI mechanism described in [SASL] + and/or the [DIGEST-MD5] mechanism. + + Servers and clients can support multiple authentication + mechanisms. The server SHOULD list its supported authentication + mechanisms in the response to the CAPABILITY command so that the + client knows which authentication mechanisms to use. + + A server MAY include a CAPABILITY response code in the tagged OK + response of a successful AUTHENTICATE command in order to send + capabilities automatically. It is unnecessary for a client to + send a separate CAPABILITY command if it recognizes these + automatic capabilities. This should only be done if a security + layer was not negotiated by the AUTHENTICATE command, because the + tagged OK response as part of an AUTHENTICATE command is not + protected by encryption/integrity checking. [SASL] requires the + client to re-issue a CAPABILITY command in this case. + + If an AUTHENTICATE command fails with a NO response, the client + MAY try another authentication mechanism by issuing another + AUTHENTICATE command. It MAY also attempt to authenticate by + using the LOGIN command (see section 6.2.3 for more detail). In + other words, the client MAY request authentication types in + decreasing order of preference, with the LOGIN command as a last + resort. + + The authorization identity passed from the client to the server + during the authentication exchange is interpreted by the server as + the user name whose privileges the client is requesting. + + + + + + + + + +Crispin Standards Track [Page 29] + +RFC 3501 IMAPv4 March 2003 + + + Example: S: * OK IMAP4rev1 Server + C: A001 AUTHENTICATE GSSAPI + S: + + C: YIIB+wYJKoZIhvcSAQICAQBuggHqMIIB5qADAgEFoQMCAQ6iBw + MFACAAAACjggEmYYIBIjCCAR6gAwIBBaESGxB1Lndhc2hpbmd0 + b24uZWR1oi0wK6ADAgEDoSQwIhsEaW1hcBsac2hpdmFtcy5jYW + Mud2FzaGluZ3Rvbi5lZHWjgdMwgdCgAwIBAaEDAgEDooHDBIHA + cS1GSa5b+fXnPZNmXB9SjL8Ollj2SKyb+3S0iXMljen/jNkpJX + AleKTz6BQPzj8duz8EtoOuNfKgweViyn/9B9bccy1uuAE2HI0y + C/PHXNNU9ZrBziJ8Lm0tTNc98kUpjXnHZhsMcz5Mx2GR6dGknb + I0iaGcRerMUsWOuBmKKKRmVMMdR9T3EZdpqsBd7jZCNMWotjhi + vd5zovQlFqQ2Wjc2+y46vKP/iXxWIuQJuDiisyXF0Y8+5GTpAL + pHDc1/pIGmMIGjoAMCAQGigZsEgZg2on5mSuxoDHEA1w9bcW9n + FdFxDKpdrQhVGVRDIzcCMCTzvUboqb5KjY1NJKJsfjRQiBYBdE + NKfzK+g5DlV8nrw81uOcP8NOQCLR5XkoMHC0Dr/80ziQzbNqhx + O6652Npft0LQwJvenwDI13YxpwOdMXzkWZN/XrEqOWp6GCgXTB + vCyLWLlWnbaUkZdEYbKHBPjd8t/1x5Yg== + S: + YGgGCSqGSIb3EgECAgIAb1kwV6ADAgEFoQMCAQ+iSzBJoAMC + AQGiQgRAtHTEuOP2BXb9sBYFR4SJlDZxmg39IxmRBOhXRKdDA0 + uHTCOT9Bq3OsUTXUlk0CsFLoa8j+gvGDlgHuqzWHPSQg== + C: + S: + YDMGCSqGSIb3EgECAgIBAAD/////6jcyG4GE3KkTzBeBiVHe + ceP2CWY0SR0fAQAgAAQEBAQ= + C: YDMGCSqGSIb3EgECAgIBAAD/////3LQBHXTpFfZgrejpLlLImP + wkhbfa2QteAQAgAG1yYwE= + S: A001 OK GSSAPI authentication successful + + Note: The line breaks within server challenges and client + responses are for editorial clarity and are not in real + authenticators. + + +6.2.3. LOGIN Command + + Arguments: user name + password + + Responses: no specific responses for this command + + Result: OK - login completed, now in authenticated state + NO - login failure: user name or password rejected + BAD - command unknown or arguments invalid + + The LOGIN command identifies the client to the server and carries + the plaintext password authenticating this user. + + + + + + +Crispin Standards Track [Page 30] + +RFC 3501 IMAPv4 March 2003 + + + A server MAY include a CAPABILITY response code in the tagged OK + response to a successful LOGIN command in order to send + capabilities automatically. It is unnecessary for a client to + send a separate CAPABILITY command if it recognizes these + automatic capabilities. + + Example: C: a001 LOGIN SMITH SESAME + S: a001 OK LOGIN completed + + Note: Use of the LOGIN command over an insecure network + (such as the Internet) is a security risk, because anyone + monitoring network traffic can obtain plaintext passwords. + The LOGIN command SHOULD NOT be used except as a last + resort, and it is recommended that client implementations + have a means to disable any automatic use of the LOGIN + command. + + Unless either the STARTTLS command has been negotiated or + some other mechanism that protects the session from + password snooping has been provided, a server + implementation MUST implement a configuration in which it + advertises the LOGINDISABLED capability and does NOT permit + the LOGIN command. Server sites SHOULD NOT use any + configuration which permits the LOGIN command without such + a protection mechanism against password snooping. A client + implementation MUST NOT send a LOGIN command if the + LOGINDISABLED capability is advertised. + +6.3. Client Commands - Authenticated State + + In the authenticated state, commands that manipulate mailboxes as + atomic entities are permitted. Of these commands, the SELECT and + EXAMINE commands will select a mailbox for access and enter the + selected state. + + In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT), + the following commands are valid in the authenticated state: SELECT, + EXAMINE, CREATE, DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB, + STATUS, and APPEND. + + + + + + + + + + + + +Crispin Standards Track [Page 31] + +RFC 3501 IMAPv4 March 2003 + + +6.3.1. SELECT Command + + Arguments: mailbox name + + Responses: REQUIRED untagged responses: FLAGS, EXISTS, RECENT + REQUIRED OK untagged responses: UNSEEN, PERMANENTFLAGS, + UIDNEXT, UIDVALIDITY + + Result: OK - select completed, now in selected state + NO - select failure, now in authenticated state: no + such mailbox, can't access mailbox + BAD - command unknown or arguments invalid + + The SELECT command selects a mailbox so that messages in the + mailbox can be accessed. Before returning an OK to the client, + the server MUST send the following untagged data to the client. + Note that earlier versions of this protocol only required the + FLAGS, EXISTS, and RECENT untagged data; consequently, client + implementations SHOULD implement default behavior for missing data + as discussed with the individual item. + + FLAGS Defined flags in the mailbox. See the description + of the FLAGS response for more detail. + + <n> EXISTS The number of messages in the mailbox. See the + description of the EXISTS response for more detail. + + <n> RECENT The number of messages with the \Recent flag set. + See the description of the RECENT response for more + detail. + + OK [UNSEEN <n>] + The message sequence number of the first unseen + message in the mailbox. If this is missing, the + client can not make any assumptions about the first + unseen message in the mailbox, and needs to issue a + SEARCH command if it wants to find it. + + OK [PERMANENTFLAGS (<list of flags>)] + A list of message flags that the client can change + permanently. If this is missing, the client should + assume that all flags can be changed permanently. + + OK [UIDNEXT <n>] + The next unique identifier value. Refer to section + 2.3.1.1 for more information. If this is missing, + the client can not make any assumptions about the + next unique identifier value. + + + +Crispin Standards Track [Page 32] + +RFC 3501 IMAPv4 March 2003 + + + OK [UIDVALIDITY <n>] + The unique identifier validity value. Refer to + section 2.3.1.1 for more information. If this is + missing, the server does not support unique + identifiers. + + Only one mailbox can be selected at a time in a connection; + simultaneous access to multiple mailboxes requires multiple + connections. The SELECT command automatically deselects any + currently selected mailbox before attempting the new selection. + Consequently, if a mailbox is selected and a SELECT command that + fails is attempted, no mailbox is selected. + + If the client is permitted to modify the mailbox, the server + SHOULD prefix the text of the tagged OK response with the + "[READ-WRITE]" response code. + + If the client is not permitted to modify the mailbox but is + permitted read access, the mailbox is selected as read-only, and + the server MUST prefix the text of the tagged OK response to + SELECT with the "[READ-ONLY]" response code. Read-only access + through SELECT differs from the EXAMINE command in that certain + read-only mailboxes MAY permit the change of permanent state on a + per-user (as opposed to global) basis. Netnews messages marked in + a server-based .newsrc file are an example of such per-user + permanent state that can be modified with read-only mailboxes. + + Example: C: A142 SELECT INBOX + S: * 172 EXISTS + S: * 1 RECENT + S: * OK [UNSEEN 12] Message 12 is first unseen + S: * OK [UIDVALIDITY 3857529045] UIDs valid + S: * OK [UIDNEXT 4392] Predicted next UID + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited + S: A142 OK [READ-WRITE] SELECT completed + + + + + + + + + + + + + + + +Crispin Standards Track [Page 33] + +RFC 3501 IMAPv4 March 2003 + + +6.3.2. EXAMINE Command + + Arguments: mailbox name + + Responses: REQUIRED untagged responses: FLAGS, EXISTS, RECENT + REQUIRED OK untagged responses: UNSEEN, PERMANENTFLAGS, + UIDNEXT, UIDVALIDITY + + Result: OK - examine completed, now in selected state + NO - examine failure, now in authenticated state: no + such mailbox, can't access mailbox + BAD - command unknown or arguments invalid + + The EXAMINE command is identical to SELECT and returns the same + output; however, the selected mailbox is identified as read-only. + No changes to the permanent state of the mailbox, including + per-user state, are permitted; in particular, EXAMINE MUST NOT + cause messages to lose the \Recent flag. + + The text of the tagged OK response to the EXAMINE command MUST + begin with the "[READ-ONLY]" response code. + + Example: C: A932 EXAMINE blurdybloop + S: * 17 EXISTS + S: * 2 RECENT + S: * OK [UNSEEN 8] Message 8 is first unseen + S: * OK [UIDVALIDITY 3857529045] UIDs valid + S: * OK [UIDNEXT 4392] Predicted next UID + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS ()] No permanent flags permitted + S: A932 OK [READ-ONLY] EXAMINE completed + + +6.3.3. CREATE Command + + Arguments: mailbox name + + Responses: no specific responses for this command + + Result: OK - create completed + NO - create failure: can't create mailbox with that name + BAD - command unknown or arguments invalid + + The CREATE command creates a mailbox with the given name. An OK + response is returned only if a new mailbox with that name has been + created. It is an error to attempt to create INBOX or a mailbox + with a name that refers to an extant mailbox. Any error in + creation will return a tagged NO response. + + + +Crispin Standards Track [Page 34] + +RFC 3501 IMAPv4 March 2003 + + + If the mailbox name is suffixed with the server's hierarchy + separator character (as returned from the server by a LIST + command), this is a declaration that the client intends to create + mailbox names under this name in the hierarchy. Server + implementations that do not require this declaration MUST ignore + the declaration. In any case, the name created is without the + trailing hierarchy delimiter. + + If the server's hierarchy separator character appears elsewhere in + the name, the server SHOULD create any superior hierarchical names + that are needed for the CREATE command to be successfully + completed. In other words, an attempt to create "foo/bar/zap" on + a server in which "/" is the hierarchy separator character SHOULD + create foo/ and foo/bar/ if they do not already exist. + + If a new mailbox is created with the same name as a mailbox which + was deleted, its unique identifiers MUST be greater than any + unique identifiers used in the previous incarnation of the mailbox + UNLESS the new incarnation has a different unique identifier + validity value. See the description of the UID command for more + detail. + + Example: C: A003 CREATE owatagusiam/ + S: A003 OK CREATE completed + C: A004 CREATE owatagusiam/blurdybloop + S: A004 OK CREATE completed + + Note: The interpretation of this example depends on whether + "/" was returned as the hierarchy separator from LIST. If + "/" is the hierarchy separator, a new level of hierarchy + named "owatagusiam" with a member called "blurdybloop" is + created. Otherwise, two mailboxes at the same hierarchy + level are created. + + +6.3.4. DELETE Command + + Arguments: mailbox name + + Responses: no specific responses for this command + + Result: OK - delete completed + NO - delete failure: can't delete mailbox with that name + BAD - command unknown or arguments invalid + + + + + + + +Crispin Standards Track [Page 35] + +RFC 3501 IMAPv4 March 2003 + + + The DELETE command permanently removes the mailbox with the given + name. A tagged OK response is returned only if the mailbox has + been deleted. It is an error to attempt to delete INBOX or a + mailbox name that does not exist. + + The DELETE command MUST NOT remove inferior hierarchical names. + For example, if a mailbox "foo" has an inferior "foo.bar" + (assuming "." is the hierarchy delimiter character), removing + "foo" MUST NOT remove "foo.bar". It is an error to attempt to + delete a name that has inferior hierarchical names and also has + the \Noselect mailbox name attribute (see the description of the + LIST response for more details). + + It is permitted to delete a name that has inferior hierarchical + names and does not have the \Noselect mailbox name attribute. In + this case, all messages in that mailbox are removed, and the name + will acquire the \Noselect mailbox name attribute. + + The value of the highest-used unique identifier of the deleted + mailbox MUST be preserved so that a new mailbox created with the + same name will not reuse the identifiers of the former + incarnation, UNLESS the new incarnation has a different unique + identifier validity value. See the description of the UID command + for more detail. + + Examples: C: A682 LIST "" * + S: * LIST () "/" blurdybloop + S: * LIST (\Noselect) "/" foo + S: * LIST () "/" foo/bar + S: A682 OK LIST completed + C: A683 DELETE blurdybloop + S: A683 OK DELETE completed + C: A684 DELETE foo + S: A684 NO Name "foo" has inferior hierarchical names + C: A685 DELETE foo/bar + S: A685 OK DELETE Completed + C: A686 LIST "" * + S: * LIST (\Noselect) "/" foo + S: A686 OK LIST completed + C: A687 DELETE foo + S: A687 OK DELETE Completed + + + + + + + + + + +Crispin Standards Track [Page 36] + +RFC 3501 IMAPv4 March 2003 + + + C: A82 LIST "" * + S: * LIST () "." blurdybloop + S: * LIST () "." foo + S: * LIST () "." foo.bar + S: A82 OK LIST completed + C: A83 DELETE blurdybloop + S: A83 OK DELETE completed + C: A84 DELETE foo + S: A84 OK DELETE Completed + C: A85 LIST "" * + S: * LIST () "." foo.bar + S: A85 OK LIST completed + C: A86 LIST "" % + S: * LIST (\Noselect) "." foo + S: A86 OK LIST completed + + +6.3.5. RENAME Command + + Arguments: existing mailbox name + new mailbox name + + Responses: no specific responses for this command + + Result: OK - rename completed + NO - rename failure: can't rename mailbox with that name, + can't rename to mailbox with that name + BAD - command unknown or arguments invalid + + The RENAME command changes the name of a mailbox. A tagged OK + response is returned only if the mailbox has been renamed. It is + an error to attempt to rename from a mailbox name that does not + exist or to a mailbox name that already exists. Any error in + renaming will return a tagged NO response. + + If the name has inferior hierarchical names, then the inferior + hierarchical names MUST also be renamed. For example, a rename of + "foo" to "zap" will rename "foo/bar" (assuming "/" is the + hierarchy delimiter character) to "zap/bar". + + If the server's hierarchy separator character appears in the name, + the server SHOULD create any superior hierarchical names that are + needed for the RENAME command to complete successfully. In other + words, an attempt to rename "foo/bar/zap" to baz/rag/zowie on a + server in which "/" is the hierarchy separator character SHOULD + create baz/ and baz/rag/ if they do not already exist. + + + + + +Crispin Standards Track [Page 37] + +RFC 3501 IMAPv4 March 2003 + + + The value of the highest-used unique identifier of the old mailbox + name MUST be preserved so that a new mailbox created with the same + name will not reuse the identifiers of the former incarnation, + UNLESS the new incarnation has a different unique identifier + validity value. See the description of the UID command for more + detail. + + Renaming INBOX is permitted, and has special behavior. It moves + all messages in INBOX to a new mailbox with the given name, + leaving INBOX empty. If the server implementation supports + inferior hierarchical names of INBOX, these are unaffected by a + rename of INBOX. + + Examples: C: A682 LIST "" * + S: * LIST () "/" blurdybloop + S: * LIST (\Noselect) "/" foo + S: * LIST () "/" foo/bar + S: A682 OK LIST completed + C: A683 RENAME blurdybloop sarasoop + S: A683 OK RENAME completed + C: A684 RENAME foo zowie + S: A684 OK RENAME Completed + C: A685 LIST "" * + S: * LIST () "/" sarasoop + S: * LIST (\Noselect) "/" zowie + S: * LIST () "/" zowie/bar + S: A685 OK LIST completed + + C: Z432 LIST "" * + S: * LIST () "." INBOX + S: * LIST () "." INBOX.bar + S: Z432 OK LIST completed + C: Z433 RENAME INBOX old-mail + S: Z433 OK RENAME completed + C: Z434 LIST "" * + S: * LIST () "." INBOX + S: * LIST () "." INBOX.bar + S: * LIST () "." old-mail + S: Z434 OK LIST completed + + + + + + + + + + + + +Crispin Standards Track [Page 38] + +RFC 3501 IMAPv4 March 2003 + + +6.3.6. SUBSCRIBE Command + + Arguments: mailbox + + Responses: no specific responses for this command + + Result: OK - subscribe completed + NO - subscribe failure: can't subscribe to that name + BAD - command unknown or arguments invalid + + The SUBSCRIBE command adds the specified mailbox name to the + server's set of "active" or "subscribed" mailboxes as returned by + the LSUB command. This command returns a tagged OK response only + if the subscription is successful. + + A server MAY validate the mailbox argument to SUBSCRIBE to verify + that it exists. However, it MUST NOT unilaterally remove an + existing mailbox name from the subscription list even if a mailbox + by that name no longer exists. + + Note: This requirement is because a server site can + choose to routinely remove a mailbox with a well-known + name (e.g., "system-alerts") after its contents expire, + with the intention of recreating it when new contents + are appropriate. + + + Example: C: A002 SUBSCRIBE #news.comp.mail.mime + S: A002 OK SUBSCRIBE completed + + +6.3.7. UNSUBSCRIBE Command + + Arguments: mailbox name + + Responses: no specific responses for this command + + Result: OK - unsubscribe completed + NO - unsubscribe failure: can't unsubscribe that name + BAD - command unknown or arguments invalid + + The UNSUBSCRIBE command removes the specified mailbox name from + the server's set of "active" or "subscribed" mailboxes as returned + by the LSUB command. This command returns a tagged OK response + only if the unsubscription is successful. + + Example: C: A002 UNSUBSCRIBE #news.comp.mail.mime + S: A002 OK UNSUBSCRIBE completed + + + +Crispin Standards Track [Page 39] + +RFC 3501 IMAPv4 March 2003 + + +6.3.8. LIST Command + + Arguments: reference name + mailbox name with possible wildcards + + Responses: untagged responses: LIST + + Result: OK - list completed + NO - list failure: can't list that reference or name + BAD - command unknown or arguments invalid + + The LIST command returns a subset of names from the complete set + of all names available to the client. Zero or more untagged LIST + replies are returned, containing the name attributes, hierarchy + delimiter, and name; see the description of the LIST reply for + more detail. + + The LIST command SHOULD return its data quickly, without undue + delay. For example, it SHOULD NOT go to excess trouble to + calculate the \Marked or \Unmarked status or perform other + processing; if each name requires 1 second of processing, then a + list of 1200 names would take 20 minutes! + + An empty ("" string) reference name argument indicates that the + mailbox name is interpreted as by SELECT. The returned mailbox + names MUST match the supplied mailbox name pattern. A non-empty + reference name argument is the name of a mailbox or a level of + mailbox hierarchy, and indicates the context in which the mailbox + name is interpreted. + + An empty ("" string) mailbox name argument is a special request to + return the hierarchy delimiter and the root name of the name given + in the reference. The value returned as the root MAY be the empty + string if the reference is non-rooted or is an empty string. In + all cases, a hierarchy delimiter (or NIL if there is no hierarchy) + is returned. This permits a client to get the hierarchy delimiter + (or find out that the mailbox names are flat) even when no + mailboxes by that name currently exist. + + The reference and mailbox name arguments are interpreted into a + canonical form that represents an unambiguous left-to-right + hierarchy. The returned mailbox names will be in the interpreted + form. + + + + + + + + +Crispin Standards Track [Page 40] + +RFC 3501 IMAPv4 March 2003 + + + Note: The interpretation of the reference argument is + implementation-defined. It depends upon whether the + server implementation has a concept of the "current + working directory" and leading "break out characters", + which override the current working directory. + + For example, on a server which exports a UNIX or NT + filesystem, the reference argument contains the current + working directory, and the mailbox name argument would + contain the name as interpreted in the current working + directory. + + If a server implementation has no concept of break out + characters, the canonical form is normally the reference + name appended with the mailbox name. Note that if the + server implements the namespace convention (section + 5.1.2), "#" is a break out character and must be treated + as such. + + If the reference argument is not a level of mailbox + hierarchy (that is, it is a \NoInferiors name), and/or + the reference argument does not end with the hierarchy + delimiter, it is implementation-dependent how this is + interpreted. For example, a reference of "foo/bar" and + mailbox name of "rag/baz" could be interpreted as + "foo/bar/rag/baz", "foo/barrag/baz", or "foo/rag/baz". + A client SHOULD NOT use such a reference argument except + at the explicit request of the user. A hierarchical + browser MUST NOT make any assumptions about server + interpretation of the reference unless the reference is + a level of mailbox hierarchy AND ends with the hierarchy + delimiter. + + Any part of the reference argument that is included in the + interpreted form SHOULD prefix the interpreted form. It SHOULD + also be in the same form as the reference name argument. This + rule permits the client to determine if the returned mailbox name + is in the context of the reference argument, or if something about + the mailbox argument overrode the reference argument. Without + this rule, the client would have to have knowledge of the server's + naming semantics including what characters are "breakouts" that + override a naming context. + + + + + + + + + +Crispin Standards Track [Page 41] + +RFC 3501 IMAPv4 March 2003 + + + For example, here are some examples of how references + and mailbox names might be interpreted on a UNIX-based + server: + + Reference Mailbox Name Interpretation + ------------ ------------ -------------- + ~smith/Mail/ foo.* ~smith/Mail/foo.* + archive/ % archive/% + #news. comp.mail.* #news.comp.mail.* + ~smith/Mail/ /usr/doc/foo /usr/doc/foo + archive/ ~fred/Mail/* ~fred/Mail/* + + The first three examples demonstrate interpretations in + the context of the reference argument. Note that + "~smith/Mail" SHOULD NOT be transformed into something + like "/u2/users/smith/Mail", or it would be impossible + for the client to determine that the interpretation was + in the context of the reference. + + The character "*" is a wildcard, and matches zero or more + characters at this position. The character "%" is similar to "*", + but it does not match a hierarchy delimiter. If the "%" wildcard + is the last character of a mailbox name argument, matching levels + of hierarchy are also returned. If these levels of hierarchy are + not also selectable mailboxes, they are returned with the + \Noselect mailbox name attribute (see the description of the LIST + response for more details). + + Server implementations are permitted to "hide" otherwise + accessible mailboxes from the wildcard characters, by preventing + certain characters or names from matching a wildcard in certain + situations. For example, a UNIX-based server might restrict the + interpretation of "*" so that an initial "/" character does not + match. + + The special name INBOX is included in the output from LIST, if + INBOX is supported by this server for this user and if the + uppercase string "INBOX" matches the interpreted reference and + mailbox name arguments with wildcards as described above. The + criteria for omitting INBOX is whether SELECT INBOX will return + failure; it is not relevant whether the user's real INBOX resides + on this or some other server. + + + + + + + + + +Crispin Standards Track [Page 42] + +RFC 3501 IMAPv4 March 2003 + + + Example: C: A101 LIST "" "" + S: * LIST (\Noselect) "/" "" + S: A101 OK LIST Completed + C: A102 LIST #news.comp.mail.misc "" + S: * LIST (\Noselect) "." #news. + S: A102 OK LIST Completed + C: A103 LIST /usr/staff/jones "" + S: * LIST (\Noselect) "/" / + S: A103 OK LIST Completed + C: A202 LIST ~/Mail/ % + S: * LIST (\Noselect) "/" ~/Mail/foo + S: * LIST () "/" ~/Mail/meetings + S: A202 OK LIST completed + + +6.3.9. LSUB Command + + Arguments: reference name + mailbox name with possible wildcards + + Responses: untagged responses: LSUB + + Result: OK - lsub completed + NO - lsub failure: can't list that reference or name + BAD - command unknown or arguments invalid + + The LSUB command returns a subset of names from the set of names + that the user has declared as being "active" or "subscribed". + Zero or more untagged LSUB replies are returned. The arguments to + LSUB are in the same form as those for LIST. + + The returned untagged LSUB response MAY contain different mailbox + flags from a LIST untagged response. If this should happen, the + flags in the untagged LIST are considered more authoritative. + + A special situation occurs when using LSUB with the % wildcard. + Consider what happens if "foo/bar" (with a hierarchy delimiter of + "/") is subscribed but "foo" is not. A "%" wildcard to LSUB must + return foo, not foo/bar, in the LSUB response, and it MUST be + flagged with the \Noselect attribute. + + The server MUST NOT unilaterally remove an existing mailbox name + from the subscription list even if a mailbox by that name no + longer exists. + + + + + + + +Crispin Standards Track [Page 43] + +RFC 3501 IMAPv4 March 2003 + + + Example: C: A002 LSUB "#news." "comp.mail.*" + S: * LSUB () "." #news.comp.mail.mime + S: * LSUB () "." #news.comp.mail.misc + S: A002 OK LSUB completed + C: A003 LSUB "#news." "comp.%" + S: * LSUB (\NoSelect) "." #news.comp.mail + S: A003 OK LSUB completed + + +6.3.10. STATUS Command + + Arguments: mailbox name + status data item names + + Responses: untagged responses: STATUS + + Result: OK - status completed + NO - status failure: no status for that name + BAD - command unknown or arguments invalid + + The STATUS command requests the status of the indicated mailbox. + It does not change the currently selected mailbox, nor does it + affect the state of any messages in the queried mailbox (in + particular, STATUS MUST NOT cause messages to lose the \Recent + flag). + + The STATUS command provides an alternative to opening a second + IMAP4rev1 connection and doing an EXAMINE command on a mailbox to + query that mailbox's status without deselecting the current + mailbox in the first IMAP4rev1 connection. + + Unlike the LIST command, the STATUS command is not guaranteed to + be fast in its response. Under certain circumstances, it can be + quite slow. In some implementations, the server is obliged to + open the mailbox read-only internally to obtain certain status + information. Also unlike the LIST command, the STATUS command + does not accept wildcards. + + Note: The STATUS command is intended to access the + status of mailboxes other than the currently selected + mailbox. Because the STATUS command can cause the + mailbox to be opened internally, and because this + information is available by other means on the selected + mailbox, the STATUS command SHOULD NOT be used on the + currently selected mailbox. + + + + + + +Crispin Standards Track [Page 44] + +RFC 3501 IMAPv4 March 2003 + + + The STATUS command MUST NOT be used as a "check for new + messages in the selected mailbox" operation (refer to + sections 7, 7.3.1, and 7.3.2 for more information about + the proper method for new message checking). + + Because the STATUS command is not guaranteed to be fast + in its results, clients SHOULD NOT expect to be able to + issue many consecutive STATUS commands and obtain + reasonable performance. + + The currently defined status data items that can be requested are: + + MESSAGES + The number of messages in the mailbox. + + RECENT + The number of messages with the \Recent flag set. + + UIDNEXT + The next unique identifier value of the mailbox. Refer to + section 2.3.1.1 for more information. + + UIDVALIDITY + The unique identifier validity value of the mailbox. Refer to + section 2.3.1.1 for more information. + + UNSEEN + The number of messages which do not have the \Seen flag set. + + + Example: C: A042 STATUS blurdybloop (UIDNEXT MESSAGES) + S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292) + S: A042 OK STATUS completed + + + + + + + + + + + + + + + + + + +Crispin Standards Track [Page 45] + +RFC 3501 IMAPv4 March 2003 + + +6.3.11. APPEND Command + + Arguments: mailbox name + OPTIONAL flag parenthesized list + OPTIONAL date/time string + message literal + + Responses: no specific responses for this command + + Result: OK - append completed + NO - append error: can't append to that mailbox, error + in flags or date/time or message text + BAD - command unknown or arguments invalid + + The APPEND command appends the literal argument as a new message + to the end of the specified destination mailbox. This argument + SHOULD be in the format of an [RFC-2822] message. 8-bit + characters are permitted in the message. A server implementation + that is unable to preserve 8-bit data properly MUST be able to + reversibly convert 8-bit APPEND data to 7-bit using a [MIME-IMB] + content transfer encoding. + + Note: There MAY be exceptions, e.g., draft messages, in + which required [RFC-2822] header lines are omitted in + the message literal argument to APPEND. The full + implications of doing so MUST be understood and + carefully weighed. + + If a flag parenthesized list is specified, the flags SHOULD be set + in the resulting message; otherwise, the flag list of the + resulting message is set to empty by default. In either case, the + Recent flag is also set. + + If a date-time is specified, the internal date SHOULD be set in + the resulting message; otherwise, the internal date of the + resulting message is set to the current date and time by default. + + If the append is unsuccessful for any reason, the mailbox MUST be + restored to its state before the APPEND attempt; no partial + appending is permitted. + + If the destination mailbox does not exist, a server MUST return an + error, and MUST NOT automatically create the mailbox. Unless it + is certain that the destination mailbox can not be created, the + server MUST send the response code "[TRYCREATE]" as the prefix of + the text of the tagged NO response. This gives a hint to the + client that it can attempt a CREATE command and retry the APPEND + if the CREATE is successful. + + + +Crispin Standards Track [Page 46] + +RFC 3501 IMAPv4 March 2003 + + + If the mailbox is currently selected, the normal new message + actions SHOULD occur. Specifically, the server SHOULD notify the + client immediately via an untagged EXISTS response. If the server + does not do so, the client MAY issue a NOOP command (or failing + that, a CHECK command) after one or more APPEND commands. + + Example: C: A003 APPEND saved-messages (\Seen) {310} + S: + Ready for literal data + C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST) + C: From: Fred Foobar <foobar@Blurdybloop.COM> + C: Subject: afternoon meeting + C: To: mooch@owatagu.siam.edu + C: Message-Id: <B27397-0100000@Blurdybloop.COM> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: Hello Joe, do you think we can meet at 3:30 tomorrow? + C: + S: A003 OK APPEND completed + + Note: The APPEND command is not used for message delivery, + because it does not provide a mechanism to transfer [SMTP] + envelope information. + +6.4. Client Commands - Selected State + + In the selected state, commands that manipulate messages in a mailbox + are permitted. + + In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT), + and the authenticated state commands (SELECT, EXAMINE, CREATE, + DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB, STATUS, and + APPEND), the following commands are valid in the selected state: + CHECK, CLOSE, EXPUNGE, SEARCH, FETCH, STORE, COPY, and UID. + +6.4.1. CHECK Command + + Arguments: none + + Responses: no specific responses for this command + + Result: OK - check completed + BAD - command unknown or arguments invalid + + The CHECK command requests a checkpoint of the currently selected + mailbox. A checkpoint refers to any implementation-dependent + housekeeping associated with the mailbox (e.g., resolving the + server's in-memory state of the mailbox with the state on its + + + +Crispin Standards Track [Page 47] + +RFC 3501 IMAPv4 March 2003 + + + disk) that is not normally executed as part of each command. A + checkpoint MAY take a non-instantaneous amount of real time to + complete. If a server implementation has no such housekeeping + considerations, CHECK is equivalent to NOOP. + + There is no guarantee that an EXISTS untagged response will happen + as a result of CHECK. NOOP, not CHECK, SHOULD be used for new + message polling. + + Example: C: FXXZ CHECK + S: FXXZ OK CHECK Completed + + +6.4.2. CLOSE Command + + Arguments: none + + Responses: no specific responses for this command + + Result: OK - close completed, now in authenticated state + BAD - command unknown or arguments invalid + + The CLOSE command permanently removes all messages that have the + \Deleted flag set from the currently selected mailbox, and returns + to the authenticated state from the selected state. No untagged + EXPUNGE responses are sent. + + No messages are removed, and no error is given, if the mailbox is + selected by an EXAMINE command or is otherwise selected read-only. + + Even if a mailbox is selected, a SELECT, EXAMINE, or LOGOUT + command MAY be issued without previously issuing a CLOSE command. + The SELECT, EXAMINE, and LOGOUT commands implicitly close the + currently selected mailbox without doing an expunge. However, + when many messages are deleted, a CLOSE-LOGOUT or CLOSE-SELECT + sequence is considerably faster than an EXPUNGE-LOGOUT or + EXPUNGE-SELECT because no untagged EXPUNGE responses (which the + client would probably ignore) are sent. + + Example: C: A341 CLOSE + S: A341 OK CLOSE completed + + + + + + + + + + +Crispin Standards Track [Page 48] + +RFC 3501 IMAPv4 March 2003 + + +6.4.3. EXPUNGE Command + + Arguments: none + + Responses: untagged responses: EXPUNGE + + Result: OK - expunge completed + NO - expunge failure: can't expunge (e.g., permission + denied) + BAD - command unknown or arguments invalid + + The EXPUNGE command permanently removes all messages that have the + \Deleted flag set from the currently selected mailbox. Before + returning an OK to the client, an untagged EXPUNGE response is + sent for each message that is removed. + + Example: C: A202 EXPUNGE + S: * 3 EXPUNGE + S: * 3 EXPUNGE + S: * 5 EXPUNGE + S: * 8 EXPUNGE + S: A202 OK EXPUNGE completed + + Note: In this example, messages 3, 4, 7, and 11 had the + \Deleted flag set. See the description of the EXPUNGE + response for further explanation. + + +6.4.4. SEARCH Command + + Arguments: OPTIONAL [CHARSET] specification + searching criteria (one or more) + + Responses: REQUIRED untagged response: SEARCH + + Result: OK - search completed + NO - search error: can't search that [CHARSET] or + criteria + BAD - command unknown or arguments invalid + + The SEARCH command searches the mailbox for messages that match + the given searching criteria. Searching criteria consist of one + or more search keys. The untagged SEARCH response from the server + contains a listing of message sequence numbers corresponding to + those messages that match the searching criteria. + + + + + + +Crispin Standards Track [Page 49] + +RFC 3501 IMAPv4 March 2003 + + + When multiple keys are specified, the result is the intersection + (AND function) of all the messages that match those keys. For + example, the criteria DELETED FROM "SMITH" SINCE 1-Feb-1994 refers + to all deleted messages from Smith that were placed in the mailbox + since February 1, 1994. A search key can also be a parenthesized + list of one or more search keys (e.g., for use with the OR and NOT + keys). + + Server implementations MAY exclude [MIME-IMB] body parts with + terminal content media types other than TEXT and MESSAGE from + consideration in SEARCH matching. + + The OPTIONAL [CHARSET] specification consists of the word + "CHARSET" followed by a registered [CHARSET]. It indicates the + [CHARSET] of the strings that appear in the search criteria. + [MIME-IMB] content transfer encodings, and [MIME-HDRS] strings in + [RFC-2822]/[MIME-IMB] headers, MUST be decoded before comparing + text in a [CHARSET] other than US-ASCII. US-ASCII MUST be + supported; other [CHARSET]s MAY be supported. + + If the server does not support the specified [CHARSET], it MUST + return a tagged NO response (not a BAD). This response SHOULD + contain the BADCHARSET response code, which MAY list the + [CHARSET]s supported by the server. + + In all search keys that use strings, a message matches the key if + the string is a substring of the field. The matching is + case-insensitive. + + The defined search keys are as follows. Refer to the Formal + Syntax section for the precise syntactic definitions of the + arguments. + + <sequence set> + Messages with message sequence numbers corresponding to the + specified message sequence number set. + + ALL + All messages in the mailbox; the default initial key for + ANDing. + + ANSWERED + Messages with the \Answered flag set. + + + + + + + + +Crispin Standards Track [Page 50] + +RFC 3501 IMAPv4 March 2003 + + + BCC <string> + Messages that contain the specified string in the envelope + structure's BCC field. + + BEFORE <date> + Messages whose internal date (disregarding time and timezone) + is earlier than the specified date. + + BODY <string> + Messages that contain the specified string in the body of the + message. + + CC <string> + Messages that contain the specified string in the envelope + structure's CC field. + + DELETED + Messages with the \Deleted flag set. + + DRAFT + Messages with the \Draft flag set. + + FLAGGED + Messages with the \Flagged flag set. + + FROM <string> + Messages that contain the specified string in the envelope + structure's FROM field. + + HEADER <field-name> <string> + Messages that have a header with the specified field-name (as + defined in [RFC-2822]) and that contains the specified string + in the text of the header (what comes after the colon). If the + string to search is zero-length, this matches all messages that + have a header line with the specified field-name regardless of + the contents. + + KEYWORD <flag> + Messages with the specified keyword flag set. + + LARGER <n> + Messages with an [RFC-2822] size larger than the specified + number of octets. + + NEW + Messages that have the \Recent flag set but not the \Seen flag. + This is functionally equivalent to "(RECENT UNSEEN)". + + + + +Crispin Standards Track [Page 51] + +RFC 3501 IMAPv4 March 2003 + + + NOT <search-key> + Messages that do not match the specified search key. + + OLD + Messages that do not have the \Recent flag set. This is + functionally equivalent to "NOT RECENT" (as opposed to "NOT + NEW"). + + ON <date> + Messages whose internal date (disregarding time and timezone) + is within the specified date. + + OR <search-key1> <search-key2> + Messages that match either search key. + + RECENT + Messages that have the \Recent flag set. + + SEEN + Messages that have the \Seen flag set. + + SENTBEFORE <date> + Messages whose [RFC-2822] Date: header (disregarding time and + timezone) is earlier than the specified date. + + SENTON <date> + Messages whose [RFC-2822] Date: header (disregarding time and + timezone) is within the specified date. + + SENTSINCE <date> + Messages whose [RFC-2822] Date: header (disregarding time and + timezone) is within or later than the specified date. + + SINCE <date> + Messages whose internal date (disregarding time and timezone) + is within or later than the specified date. + + SMALLER <n> + Messages with an [RFC-2822] size smaller than the specified + number of octets. + + + + + + + + + + + +Crispin Standards Track [Page 52] + +RFC 3501 IMAPv4 March 2003 + + + SUBJECT <string> + Messages that contain the specified string in the envelope + structure's SUBJECT field. + + TEXT <string> + Messages that contain the specified string in the header or + body of the message. + + TO <string> + Messages that contain the specified string in the envelope + structure's TO field. + + UID <sequence set> + Messages with unique identifiers corresponding to the specified + unique identifier set. Sequence set ranges are permitted. + + UNANSWERED + Messages that do not have the \Answered flag set. + + UNDELETED + Messages that do not have the \Deleted flag set. + + UNDRAFT + Messages that do not have the \Draft flag set. + + UNFLAGGED + Messages that do not have the \Flagged flag set. + + UNKEYWORD <flag> + Messages that do not have the specified keyword flag set. + + UNSEEN + Messages that do not have the \Seen flag set. + + + + + + + + + + + + + + + + + + +Crispin Standards Track [Page 53] + +RFC 3501 IMAPv4 March 2003 + + + Example: C: A282 SEARCH FLAGGED SINCE 1-Feb-1994 NOT FROM "Smith" + S: * SEARCH 2 84 882 + S: A282 OK SEARCH completed + C: A283 SEARCH TEXT "string not in mailbox" + S: * SEARCH + S: A283 OK SEARCH completed + C: A284 SEARCH CHARSET UTF-8 TEXT {6} + C: XXXXXX + S: * SEARCH 43 + S: A284 OK SEARCH completed + + Note: Since this document is restricted to 7-bit ASCII + text, it is not possible to show actual UTF-8 data. The + "XXXXXX" is a placeholder for what would be 6 octets of + 8-bit data in an actual transaction. + + +6.4.5. FETCH Command + + Arguments: sequence set + message data item names or macro + + Responses: untagged responses: FETCH + + Result: OK - fetch completed + NO - fetch error: can't fetch that data + BAD - command unknown or arguments invalid + + The FETCH command retrieves data associated with a message in the + mailbox. The data items to be fetched can be either a single atom + or a parenthesized list. + + Most data items, identified in the formal syntax under the + msg-att-static rule, are static and MUST NOT change for any + particular message. Other data items, identified in the formal + syntax under the msg-att-dynamic rule, MAY change, either as a + result of a STORE command or due to external events. + + For example, if a client receives an ENVELOPE for a + message when it already knows the envelope, it can + safely ignore the newly transmitted envelope. + + There are three macros which specify commonly-used sets of data + items, and can be used instead of data items. A macro must be + used by itself, and not in conjunction with other macros or data + items. + + + + + +Crispin Standards Track [Page 54] + +RFC 3501 IMAPv4 March 2003 + + + ALL + Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE ENVELOPE) + + FAST + Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE) + + FULL + Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE ENVELOPE + BODY) + + The currently defined data items that can be fetched are: + + BODY + Non-extensible form of BODYSTRUCTURE. + + BODY[<section>]<<partial>> + The text of a particular body section. The section + specification is a set of zero or more part specifiers + delimited by periods. A part specifier is either a part number + or one of the following: HEADER, HEADER.FIELDS, + HEADER.FIELDS.NOT, MIME, and TEXT. An empty section + specification refers to the entire message, including the + header. + + Every message has at least one part number. Non-[MIME-IMB] + messages, and non-multipart [MIME-IMB] messages with no + encapsulated message, only have a part 1. + + Multipart messages are assigned consecutive part numbers, as + they occur in the message. If a particular part is of type + message or multipart, its parts MUST be indicated by a period + followed by the part number within that nested multipart part. + + A part of type MESSAGE/RFC822 also has nested part numbers, + referring to parts of the MESSAGE part's body. + + The HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, and TEXT part + specifiers can be the sole part specifier or can be prefixed by + one or more numeric part specifiers, provided that the numeric + part specifier refers to a part of type MESSAGE/RFC822. The + MIME part specifier MUST be prefixed by one or more numeric + part specifiers. + + The HEADER, HEADER.FIELDS, and HEADER.FIELDS.NOT part + specifiers refer to the [RFC-2822] header of the message or of + an encapsulated [MIME-IMT] MESSAGE/RFC822 message. + HEADER.FIELDS and HEADER.FIELDS.NOT are followed by a list of + field-name (as defined in [RFC-2822]) names, and return a + + + +Crispin Standards Track [Page 55] + +RFC 3501 IMAPv4 March 2003 + + + subset of the header. The subset returned by HEADER.FIELDS + contains only those header fields with a field-name that + matches one of the names in the list; similarly, the subset + returned by HEADER.FIELDS.NOT contains only the header fields + with a non-matching field-name. The field-matching is + case-insensitive but otherwise exact. Subsetting does not + exclude the [RFC-2822] delimiting blank line between the header + and the body; the blank line is included in all header fetches, + except in the case of a message which has no body and no blank + line. + + The MIME part specifier refers to the [MIME-IMB] header for + this part. + + The TEXT part specifier refers to the text body of the message, + omitting the [RFC-2822] header. + + Here is an example of a complex message with some of its + part specifiers: + + HEADER ([RFC-2822] header of the message) + TEXT ([RFC-2822] text body of the message) MULTIPART/MIXED + 1 TEXT/PLAIN + 2 APPLICATION/OCTET-STREAM + 3 MESSAGE/RFC822 + 3.HEADER ([RFC-2822] header of the message) + 3.TEXT ([RFC-2822] text body of the message) MULTIPART/MIXED + 3.1 TEXT/PLAIN + 3.2 APPLICATION/OCTET-STREAM + 4 MULTIPART/MIXED + 4.1 IMAGE/GIF + 4.1.MIME ([MIME-IMB] header for the IMAGE/GIF) + 4.2 MESSAGE/RFC822 + 4.2.HEADER ([RFC-2822] header of the message) + 4.2.TEXT ([RFC-2822] text body of the message) MULTIPART/MIXED + 4.2.1 TEXT/PLAIN + 4.2.2 MULTIPART/ALTERNATIVE + 4.2.2.1 TEXT/PLAIN + 4.2.2.2 TEXT/RICHTEXT + + + It is possible to fetch a substring of the designated text. + This is done by appending an open angle bracket ("<"), the + octet position of the first desired octet, a period, the + maximum number of octets desired, and a close angle bracket + (">") to the part specifier. If the starting octet is beyond + the end of the text, an empty string is returned. + + + + +Crispin Standards Track [Page 56] + +RFC 3501 IMAPv4 March 2003 + + + Any partial fetch that attempts to read beyond the end of the + text is truncated as appropriate. A partial fetch that starts + at octet 0 is returned as a partial fetch, even if this + truncation happened. + + Note: This means that BODY[]<0.2048> of a 1500-octet message + will return BODY[]<0> with a literal of size 1500, not + BODY[]. + + Note: A substring fetch of a HEADER.FIELDS or + HEADER.FIELDS.NOT part specifier is calculated after + subsetting the header. + + The \Seen flag is implicitly set; if this causes the flags to + change, they SHOULD be included as part of the FETCH responses. + + BODY.PEEK[<section>]<<partial>> + An alternate form of BODY[<section>] that does not implicitly + set the \Seen flag. + + BODYSTRUCTURE + The [MIME-IMB] body structure of the message. This is computed + by the server by parsing the [MIME-IMB] header fields in the + [RFC-2822] header and [MIME-IMB] headers. + + ENVELOPE + The envelope structure of the message. This is computed by the + server by parsing the [RFC-2822] header into the component + parts, defaulting various fields as necessary. + + FLAGS + The flags that are set for this message. + + INTERNALDATE + The internal date of the message. + + RFC822 + Functionally equivalent to BODY[], differing in the syntax of + the resulting untagged FETCH data (RFC822 is returned). + + RFC822.HEADER + Functionally equivalent to BODY.PEEK[HEADER], differing in the + syntax of the resulting untagged FETCH data (RFC822.HEADER is + returned). + + RFC822.SIZE + The [RFC-2822] size of the message. + + + + +Crispin Standards Track [Page 57] + +RFC 3501 IMAPv4 March 2003 + + + RFC822.TEXT + Functionally equivalent to BODY[TEXT], differing in the syntax + of the resulting untagged FETCH data (RFC822.TEXT is returned). + + UID + The unique identifier for the message. + + + Example: C: A654 FETCH 2:4 (FLAGS BODY[HEADER.FIELDS (DATE FROM)]) + S: * 2 FETCH .... + S: * 3 FETCH .... + S: * 4 FETCH .... + S: A654 OK FETCH completed + + +6.4.6. STORE Command + + Arguments: sequence set + message data item name + value for message data item + + Responses: untagged responses: FETCH + + Result: OK - store completed + NO - store error: can't store that data + BAD - command unknown or arguments invalid + + The STORE command alters data associated with a message in the + mailbox. Normally, STORE will return the updated value of the + data with an untagged FETCH response. A suffix of ".SILENT" in + the data item name prevents the untagged FETCH, and the server + SHOULD assume that the client has determined the updated value + itself or does not care about the updated value. + + Note: Regardless of whether or not the ".SILENT" suffix + was used, the server SHOULD send an untagged FETCH + response if a change to a message's flags from an + external source is observed. The intent is that the + status of the flags is determinate without a race + condition. + + + + + + + + + + + +Crispin Standards Track [Page 58] + +RFC 3501 IMAPv4 March 2003 + + + The currently defined data items that can be stored are: + + FLAGS <flag list> + Replace the flags for the message (other than \Recent) with the + argument. The new value of the flags is returned as if a FETCH + of those flags was done. + + FLAGS.SILENT <flag list> + Equivalent to FLAGS, but without returning a new value. + + +FLAGS <flag list> + Add the argument to the flags for the message. The new value + of the flags is returned as if a FETCH of those flags was done. + + +FLAGS.SILENT <flag list> + Equivalent to +FLAGS, but without returning a new value. + + -FLAGS <flag list> + Remove the argument from the flags for the message. The new + value of the flags is returned as if a FETCH of those flags was + done. + + -FLAGS.SILENT <flag list> + Equivalent to -FLAGS, but without returning a new value. + + + Example: C: A003 STORE 2:4 +FLAGS (\Deleted) + S: * 2 FETCH (FLAGS (\Deleted \Seen)) + S: * 3 FETCH (FLAGS (\Deleted)) + S: * 4 FETCH (FLAGS (\Deleted \Flagged \Seen)) + S: A003 OK STORE completed + + +6.4.7. COPY Command + + Arguments: sequence set + mailbox name + + Responses: no specific responses for this command + + Result: OK - copy completed + NO - copy error: can't copy those messages or to that + name + BAD - command unknown or arguments invalid + + + + + + + +Crispin Standards Track [Page 59] + +RFC 3501 IMAPv4 March 2003 + + + The COPY command copies the specified message(s) to the end of the + specified destination mailbox. The flags and internal date of the + message(s) SHOULD be preserved, and the Recent flag SHOULD be set, + in the copy. + + If the destination mailbox does not exist, a server SHOULD return + an error. It SHOULD NOT automatically create the mailbox. Unless + it is certain that the destination mailbox can not be created, the + server MUST send the response code "[TRYCREATE]" as the prefix of + the text of the tagged NO response. This gives a hint to the + client that it can attempt a CREATE command and retry the COPY if + the CREATE is successful. + + If the COPY command is unsuccessful for any reason, server + implementations MUST restore the destination mailbox to its state + before the COPY attempt. + + Example: C: A003 COPY 2:4 MEETING + S: A003 OK COPY completed + + +6.4.8. UID Command + + Arguments: command name + command arguments + + Responses: untagged responses: FETCH, SEARCH + + Result: OK - UID command completed + NO - UID command error + BAD - command unknown or arguments invalid + + The UID command has two forms. In the first form, it takes as its + arguments a COPY, FETCH, or STORE command with arguments + appropriate for the associated command. However, the numbers in + the sequence set argument are unique identifiers instead of + message sequence numbers. Sequence set ranges are permitted, but + there is no guarantee that unique identifiers will be contiguous. + + A non-existent unique identifier is ignored without any error + message generated. Thus, it is possible for a UID FETCH command + to return an OK without any data or a UID COPY or UID STORE to + return an OK without performing any operations. + + In the second form, the UID command takes a SEARCH command with + SEARCH command arguments. The interpretation of the arguments is + the same as with SEARCH; however, the numbers returned in a SEARCH + response for a UID SEARCH command are unique identifiers instead + + + +Crispin Standards Track [Page 60] + +RFC 3501 IMAPv4 March 2003 + + + of message sequence numbers. For example, the command UID SEARCH + 1:100 UID 443:557 returns the unique identifiers corresponding to + the intersection of two sequence sets, the message sequence number + range 1:100 and the UID range 443:557. + + Note: in the above example, the UID range 443:557 + appears. The same comment about a non-existent unique + identifier being ignored without any error message also + applies here. Hence, even if neither UID 443 or 557 + exist, this range is valid and would include an existing + UID 495. + + Also note that a UID range of 559:* always includes the + UID of the last message in the mailbox, even if 559 is + higher than any assigned UID value. This is because the + contents of a range are independent of the order of the + range endpoints. Thus, any UID range with * as one of + the endpoints indicates at least one message (the + message with the highest numbered UID), unless the + mailbox is empty. + + The number after the "*" in an untagged FETCH response is always a + message sequence number, not a unique identifier, even for a UID + command response. However, server implementations MUST implicitly + include the UID message data item as part of any FETCH response + caused by a UID command, regardless of whether a UID was specified + as a message data item to the FETCH. + + + Note: The rule about including the UID message data item as part + of a FETCH response primarily applies to the UID FETCH and UID + STORE commands, including a UID FETCH command that does not + include UID as a message data item. Although it is unlikely that + the other UID commands will cause an untagged FETCH, this rule + applies to these commands as well. + + Example: C: A999 UID FETCH 4827313:4828442 FLAGS + S: * 23 FETCH (FLAGS (\Seen) UID 4827313) + S: * 24 FETCH (FLAGS (\Seen) UID 4827943) + S: * 25 FETCH (FLAGS (\Seen) UID 4828442) + S: A999 OK UID FETCH completed + + + + + + + + + + +Crispin Standards Track [Page 61] + +RFC 3501 IMAPv4 March 2003 + + +6.5. Client Commands - Experimental/Expansion + + +6.5.1. X<atom> Command + + Arguments: implementation defined + + Responses: implementation defined + + Result: OK - command completed + NO - failure + BAD - command unknown or arguments invalid + + Any command prefixed with an X is an experimental command. + Commands which are not part of this specification, a standard or + standards-track revision of this specification, or an + IESG-approved experimental protocol, MUST use the X prefix. + + Any added untagged responses issued by an experimental command + MUST also be prefixed with an X. Server implementations MUST NOT + send any such untagged responses, unless the client requested it + by issuing the associated experimental command. + + Example: C: a441 CAPABILITY + S: * CAPABILITY IMAP4rev1 XPIG-LATIN + S: a441 OK CAPABILITY completed + C: A442 XPIG-LATIN + S: * XPIG-LATIN ow-nay eaking-spay ig-pay atin-lay + S: A442 OK XPIG-LATIN ompleted-cay + +7. Server Responses + + Server responses are in three forms: status responses, server data, + and command continuation request. The information contained in a + server response, identified by "Contents:" in the response + descriptions below, is described by function, not by syntax. The + precise syntax of server responses is described in the Formal Syntax + section. + + The client MUST be prepared to accept any response at all times. + + Status responses can be tagged or untagged. Tagged status responses + indicate the completion result (OK, NO, or BAD status) of a client + command, and have a tag matching the command. + + Some status responses, and all server data, are untagged. An + untagged response is indicated by the token "*" instead of a tag. + Untagged status responses indicate server greeting, or server status + + + +Crispin Standards Track [Page 62] + +RFC 3501 IMAPv4 March 2003 + + + that does not indicate the completion of a command (for example, an + impending system shutdown alert). For historical reasons, untagged + server data responses are also called "unsolicited data", although + strictly speaking, only unilateral server data is truly + "unsolicited". + + Certain server data MUST be recorded by the client when it is + received; this is noted in the description of that data. Such data + conveys critical information which affects the interpretation of all + subsequent commands and responses (e.g., updates reflecting the + creation or destruction of messages). + + Other server data SHOULD be recorded for later reference; if the + client does not need to record the data, or if recording the data has + no obvious purpose (e.g., a SEARCH response when no SEARCH command is + in progress), the data SHOULD be ignored. + + An example of unilateral untagged server data occurs when the IMAP + connection is in the selected state. In the selected state, the + server checks the mailbox for new messages as part of command + execution. Normally, this is part of the execution of every command; + hence, a NOOP command suffices to check for new messages. If new + messages are found, the server sends untagged EXISTS and RECENT + responses reflecting the new size of the mailbox. Server + implementations that offer multiple simultaneous access to the same + mailbox SHOULD also send appropriate unilateral untagged FETCH and + EXPUNGE responses if another agent changes the state of any message + flags or expunges any messages. + + Command continuation request responses use the token "+" instead of a + tag. These responses are sent by the server to indicate acceptance + of an incomplete client command and readiness for the remainder of + the command. + +7.1. Server Responses - Status Responses + + Status responses are OK, NO, BAD, PREAUTH and BYE. OK, NO, and BAD + can be tagged or untagged. PREAUTH and BYE are always untagged. + + Status responses MAY include an OPTIONAL "response code". A response + code consists of data inside square brackets in the form of an atom, + possibly followed by a space and arguments. The response code + contains additional information or status codes for client software + beyond the OK/NO/BAD condition, and are defined when there is a + specific action that a client can take based upon the additional + information. + + + + + +Crispin Standards Track [Page 63] + +RFC 3501 IMAPv4 March 2003 + + + The currently defined response codes are: + + ALERT + + The human-readable text contains a special alert that MUST be + presented to the user in a fashion that calls the user's + attention to the message. + + BADCHARSET + + Optionally followed by a parenthesized list of charsets. A + SEARCH failed because the given charset is not supported by + this implementation. If the optional list of charsets is + given, this lists the charsets that are supported by this + implementation. + + CAPABILITY + + Followed by a list of capabilities. This can appear in the + initial OK or PREAUTH response to transmit an initial + capabilities list. This makes it unnecessary for a client to + send a separate CAPABILITY command if it recognizes this + response. + + PARSE + + The human-readable text represents an error in parsing the + [RFC-2822] header or [MIME-IMB] headers of a message in the + mailbox. + + PERMANENTFLAGS + + Followed by a parenthesized list of flags, indicates which of + the known flags the client can change permanently. Any flags + that are in the FLAGS untagged response, but not the + PERMANENTFLAGS list, can not be set permanently. If the client + attempts to STORE a flag that is not in the PERMANENTFLAGS + list, the server will either ignore the change or store the + state change for the remainder of the current session only. + The PERMANENTFLAGS list can also include the special flag \*, + which indicates that it is possible to create new keywords by + attempting to store those flags in the mailbox. + + + + + + + + + +Crispin Standards Track [Page 64] + +RFC 3501 IMAPv4 March 2003 + + + READ-ONLY + + The mailbox is selected read-only, or its access while selected + has changed from read-write to read-only. + + READ-WRITE + + The mailbox is selected read-write, or its access while + selected has changed from read-only to read-write. + + TRYCREATE + + An APPEND or COPY attempt is failing because the target mailbox + does not exist (as opposed to some other reason). This is a + hint to the client that the operation can succeed if the + mailbox is first created by the CREATE command. + + UIDNEXT + + Followed by a decimal number, indicates the next unique + identifier value. Refer to section 2.3.1.1 for more + information. + + UIDVALIDITY + + Followed by a decimal number, indicates the unique identifier + validity value. Refer to section 2.3.1.1 for more information. + + UNSEEN + + Followed by a decimal number, indicates the number of the first + message without the \Seen flag set. + + Additional response codes defined by particular client or server + implementations SHOULD be prefixed with an "X" until they are + added to a revision of this protocol. Client implementations + SHOULD ignore response codes that they do not recognize. + +7.1.1. OK Response + + Contents: OPTIONAL response code + human-readable text + + The OK response indicates an information message from the server. + When tagged, it indicates successful completion of the associated + command. The human-readable text MAY be presented to the user as + an information message. The untagged form indicates an + + + + +Crispin Standards Track [Page 65] + +RFC 3501 IMAPv4 March 2003 + + + information-only message; the nature of the information MAY be + indicated by a response code. + + The untagged form is also used as one of three possible greetings + at connection startup. It indicates that the connection is not + yet authenticated and that a LOGIN command is needed. + + Example: S: * OK IMAP4rev1 server ready + C: A001 LOGIN fred blurdybloop + S: * OK [ALERT] System shutdown in 10 minutes + S: A001 OK LOGIN Completed + + +7.1.2. NO Response + + Contents: OPTIONAL response code + human-readable text + + The NO response indicates an operational error message from the + server. When tagged, it indicates unsuccessful completion of the + associated command. The untagged form indicates a warning; the + command can still complete successfully. The human-readable text + describes the condition. + + Example: C: A222 COPY 1:2 owatagusiam + S: * NO Disk is 98% full, please delete unnecessary data + S: A222 OK COPY completed + C: A223 COPY 3:200 blurdybloop + S: * NO Disk is 98% full, please delete unnecessary data + S: * NO Disk is 99% full, please delete unnecessary data + S: A223 NO COPY failed: disk is full + + +7.1.3. BAD Response + + Contents: OPTIONAL response code + human-readable text + + The BAD response indicates an error message from the server. When + tagged, it reports a protocol-level error in the client's command; + the tag indicates the command that caused the error. The untagged + form indicates a protocol-level error for which the associated + command can not be determined; it can also indicate an internal + server failure. The human-readable text describes the condition. + + + + + + + +Crispin Standards Track [Page 66] + +RFC 3501 IMAPv4 March 2003 + + + Example: C: ...very long command line... + S: * BAD Command line too long + C: ...empty line... + S: * BAD Empty command line + C: A443 EXPUNGE + S: * BAD Disk crash, attempting salvage to a new disk! + S: * OK Salvage successful, no data lost + S: A443 OK Expunge completed + + +7.1.4. PREAUTH Response + + Contents: OPTIONAL response code + human-readable text + + The PREAUTH response is always untagged, and is one of three + possible greetings at connection startup. It indicates that the + connection has already been authenticated by external means; thus + no LOGIN command is needed. + + Example: S: * PREAUTH IMAP4rev1 server logged in as Smith + + +7.1.5. BYE Response + + Contents: OPTIONAL response code + human-readable text + + The BYE response is always untagged, and indicates that the server + is about to close the connection. The human-readable text MAY be + displayed to the user in a status report by the client. The BYE + response is sent under one of four conditions: + + 1) as part of a normal logout sequence. The server will close + the connection after sending the tagged OK response to the + LOGOUT command. + + 2) as a panic shutdown announcement. The server closes the + connection immediately. + + 3) as an announcement of an inactivity autologout. The server + closes the connection immediately. + + 4) as one of three possible greetings at connection startup, + indicating that the server is not willing to accept a + connection from this client. The server closes the + connection immediately. + + + + +Crispin Standards Track [Page 67] + +RFC 3501 IMAPv4 March 2003 + + + The difference between a BYE that occurs as part of a normal + LOGOUT sequence (the first case) and a BYE that occurs because of + a failure (the other three cases) is that the connection closes + immediately in the failure case. In all cases the client SHOULD + continue to read response data from the server until the + connection is closed; this will ensure that any pending untagged + or completion responses are read and processed. + + Example: S: * BYE Autologout; idle for too long + +7.2. Server Responses - Server and Mailbox Status + + These responses are always untagged. This is how server and mailbox + status data are transmitted from the server to the client. Many of + these responses typically result from a command with the same name. + +7.2.1. CAPABILITY Response + + Contents: capability listing + + The CAPABILITY response occurs as a result of a CAPABILITY + command. The capability listing contains a space-separated + listing of capability names that the server supports. The + capability listing MUST include the atom "IMAP4rev1". + + In addition, client and server implementations MUST implement the + STARTTLS, LOGINDISABLED, and AUTH=PLAIN (described in [IMAP-TLS]) + capabilities. See the Security Considerations section for + important information. + + A capability name which begins with "AUTH=" indicates that the + server supports that particular authentication mechanism. + + The LOGINDISABLED capability indicates that the LOGIN command is + disabled, and that the server will respond with a tagged NO + response to any attempt to use the LOGIN command even if the user + name and password are valid. An IMAP client MUST NOT issue the + LOGIN command if the server advertises the LOGINDISABLED + capability. + + Other capability names indicate that the server supports an + extension, revision, or amendment to the IMAP4rev1 protocol. + Server responses MUST conform to this document until the client + issues a command that uses the associated capability. + + Capability names MUST either begin with "X" or be standard or + standards-track IMAP4rev1 extensions, revisions, or amendments + registered with IANA. A server MUST NOT offer unregistered or + + + +Crispin Standards Track [Page 68] + +RFC 3501 IMAPv4 March 2003 + + + non-standard capability names, unless such names are prefixed with + an "X". + + Client implementations SHOULD NOT require any capability name + other than "IMAP4rev1", and MUST ignore any unknown capability + names. + + A server MAY send capabilities automatically, by using the + CAPABILITY response code in the initial PREAUTH or OK responses, + and by sending an updated CAPABILITY response code in the tagged + OK response as part of a successful authentication. It is + unnecessary for a client to send a separate CAPABILITY command if + it recognizes these automatic capabilities. + + Example: S: * CAPABILITY IMAP4rev1 STARTTLS AUTH=GSSAPI XPIG-LATIN + + +7.2.2. LIST Response + + Contents: name attributes + hierarchy delimiter + name + + The LIST response occurs as a result of a LIST command. It + returns a single name that matches the LIST specification. There + can be multiple LIST responses for a single LIST command. + + Four name attributes are defined: + + \Noinferiors + It is not possible for any child levels of hierarchy to exist + under this name; no child levels exist now and none can be + created in the future. + + \Noselect + It is not possible to use this name as a selectable mailbox. + + \Marked + The mailbox has been marked "interesting" by the server; the + mailbox probably contains messages that have been added since + the last time the mailbox was selected. + + \Unmarked + The mailbox does not contain any additional messages since the + last time the mailbox was selected. + + + + + + +Crispin Standards Track [Page 69] + +RFC 3501 IMAPv4 March 2003 + + + If it is not feasible for the server to determine whether or not + the mailbox is "interesting", or if the name is a \Noselect name, + the server SHOULD NOT send either \Marked or \Unmarked. + + The hierarchy delimiter is a character used to delimit levels of + hierarchy in a mailbox name. A client can use it to create child + mailboxes, and to search higher or lower levels of naming + hierarchy. All children of a top-level hierarchy node MUST use + the same separator character. A NIL hierarchy delimiter means + that no hierarchy exists; the name is a "flat" name. + + The name represents an unambiguous left-to-right hierarchy, and + MUST be valid for use as a reference in LIST and LSUB commands. + Unless \Noselect is indicated, the name MUST also be valid as an + argument for commands, such as SELECT, that accept mailbox names. + + Example: S: * LIST (\Noselect) "/" ~/Mail/foo + + +7.2.3. LSUB Response + + Contents: name attributes + hierarchy delimiter + name + + The LSUB response occurs as a result of an LSUB command. It + returns a single name that matches the LSUB specification. There + can be multiple LSUB responses for a single LSUB command. The + data is identical in format to the LIST response. + + Example: S: * LSUB () "." #news.comp.mail.misc + + +7.2.4 STATUS Response + + Contents: name + status parenthesized list + + The STATUS response occurs as a result of an STATUS command. It + returns the mailbox name that matches the STATUS specification and + the requested mailbox status information. + + Example: S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292) + + + + + + + + +Crispin Standards Track [Page 70] + +RFC 3501 IMAPv4 March 2003 + + +7.2.5. SEARCH Response + + Contents: zero or more numbers + + The SEARCH response occurs as a result of a SEARCH or UID SEARCH + command. The number(s) refer to those messages that match the + search criteria. For SEARCH, these are message sequence numbers; + for UID SEARCH, these are unique identifiers. Each number is + delimited by a space. + + Example: S: * SEARCH 2 3 6 + + +7.2.6. FLAGS Response + + Contents: flag parenthesized list + + The FLAGS response occurs as a result of a SELECT or EXAMINE + command. The flag parenthesized list identifies the flags (at a + minimum, the system-defined flags) that are applicable for this + mailbox. Flags other than the system flags can also exist, + depending on server implementation. + + The update from the FLAGS response MUST be recorded by the client. + + Example: S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + + +7.3. Server Responses - Mailbox Size + + These responses are always untagged. This is how changes in the size + of the mailbox are transmitted from the server to the client. + Immediately following the "*" token is a number that represents a + message count. + +7.3.1. EXISTS Response + + Contents: none + + The EXISTS response reports the number of messages in the mailbox. + This response occurs as a result of a SELECT or EXAMINE command, + and if the size of the mailbox changes (e.g., new messages). + + The update from the EXISTS response MUST be recorded by the + client. + + Example: S: * 23 EXISTS + + + + +Crispin Standards Track [Page 71] + +RFC 3501 IMAPv4 March 2003 + + +7.3.2. RECENT Response + + Contents: none + + The RECENT response reports the number of messages with the + \Recent flag set. This response occurs as a result of a SELECT or + EXAMINE command, and if the size of the mailbox changes (e.g., new + messages). + + Note: It is not guaranteed that the message sequence + numbers of recent messages will be a contiguous range of + the highest n messages in the mailbox (where n is the + value reported by the RECENT response). Examples of + situations in which this is not the case are: multiple + clients having the same mailbox open (the first session + to be notified will see it as recent, others will + probably see it as non-recent), and when the mailbox is + re-ordered by a non-IMAP agent. + + The only reliable way to identify recent messages is to + look at message flags to see which have the \Recent flag + set, or to do a SEARCH RECENT. + + The update from the RECENT response MUST be recorded by the + client. + + Example: S: * 5 RECENT + + +7.4. Server Responses - Message Status + + These responses are always untagged. This is how message data are + transmitted from the server to the client, often as a result of a + command with the same name. Immediately following the "*" token is a + number that represents a message sequence number. + +7.4.1. EXPUNGE Response + + Contents: none + + The EXPUNGE response reports that the specified message sequence + number has been permanently removed from the mailbox. The message + sequence number for each successive message in the mailbox is + immediately decremented by 1, and this decrement is reflected in + message sequence numbers in subsequent responses (including other + untagged EXPUNGE responses). + + + + + +Crispin Standards Track [Page 72] + +RFC 3501 IMAPv4 March 2003 + + + The EXPUNGE response also decrements the number of messages in the + mailbox; it is not necessary to send an EXISTS response with the + new value. + + As a result of the immediate decrement rule, message sequence + numbers that appear in a set of successive EXPUNGE responses + depend upon whether the messages are removed starting from lower + numbers to higher numbers, or from higher numbers to lower + numbers. For example, if the last 5 messages in a 9-message + mailbox are expunged, a "lower to higher" server will send five + untagged EXPUNGE responses for message sequence number 5, whereas + a "higher to lower server" will send successive untagged EXPUNGE + responses for message sequence numbers 9, 8, 7, 6, and 5. + + An EXPUNGE response MUST NOT be sent when no command is in + progress, nor while responding to a FETCH, STORE, or SEARCH + command. This rule is necessary to prevent a loss of + synchronization of message sequence numbers between client and + server. A command is not "in progress" until the complete command + has been received; in particular, a command is not "in progress" + during the negotiation of command continuation. + + Note: UID FETCH, UID STORE, and UID SEARCH are different + commands from FETCH, STORE, and SEARCH. An EXPUNGE + response MAY be sent during a UID command. + + The update from the EXPUNGE response MUST be recorded by the + client. + + Example: S: * 44 EXPUNGE + + +7.4.2. FETCH Response + + Contents: message data + + The FETCH response returns data about a message to the client. + The data are pairs of data item names and their values in + parentheses. This response occurs as the result of a FETCH or + STORE command, as well as by unilateral server decision (e.g., + flag updates). + + The current data items are: + + BODY + A form of BODYSTRUCTURE without extension data. + + + + + +Crispin Standards Track [Page 73] + +RFC 3501 IMAPv4 March 2003 + + + BODY[<section>]<<origin octet>> + A string expressing the body contents of the specified section. + The string SHOULD be interpreted by the client according to the + content transfer encoding, body type, and subtype. + + If the origin octet is specified, this string is a substring of + the entire body contents, starting at that origin octet. This + means that BODY[]<0> MAY be truncated, but BODY[] is NEVER + truncated. + + Note: The origin octet facility MUST NOT be used by a server + in a FETCH response unless the client specifically requested + it by means of a FETCH of a BODY[<section>]<<partial>> data + item. + + 8-bit textual data is permitted if a [CHARSET] identifier is + part of the body parameter parenthesized list for this section. + Note that headers (part specifiers HEADER or MIME, or the + header portion of a MESSAGE/RFC822 part), MUST be 7-bit; 8-bit + characters are not permitted in headers. Note also that the + [RFC-2822] delimiting blank line between the header and the + body is not affected by header line subsetting; the blank line + is always included as part of header data, except in the case + of a message which has no body and no blank line. + + Non-textual data such as binary data MUST be transfer encoded + into a textual form, such as BASE64, prior to being sent to the + client. To derive the original binary data, the client MUST + decode the transfer encoded string. + + BODYSTRUCTURE + A parenthesized list that describes the [MIME-IMB] body + structure of a message. This is computed by the server by + parsing the [MIME-IMB] header fields, defaulting various fields + as necessary. + + For example, a simple text message of 48 lines and 2279 octets + can have a body structure of: ("TEXT" "PLAIN" ("CHARSET" + "US-ASCII") NIL NIL "7BIT" 2279 48) + + Multiple parts are indicated by parenthesis nesting. Instead + of a body type as the first element of the parenthesized list, + there is a sequence of one or more nested body structures. The + second element of the parenthesized list is the multipart + subtype (mixed, digest, parallel, alternative, etc.). + + + + + + +Crispin Standards Track [Page 74] + +RFC 3501 IMAPv4 March 2003 + + + For example, a two part message consisting of a text and a + BASE64-encoded text attachment can have a body structure of: + (("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 1152 + 23)("TEXT" "PLAIN" ("CHARSET" "US-ASCII" "NAME" "cc.diff") + "<960723163407.20117h@cac.washington.edu>" "Compiler diff" + "BASE64" 4554 73) "MIXED") + + Extension data follows the multipart subtype. Extension data + is never returned with the BODY fetch, but can be returned with + a BODYSTRUCTURE fetch. Extension data, if present, MUST be in + the defined order. The extension data of a multipart body part + are in the following order: + + body parameter parenthesized list + A parenthesized list of attribute/value pairs [e.g., ("foo" + "bar" "baz" "rag") where "bar" is the value of "foo", and + "rag" is the value of "baz"] as defined in [MIME-IMB]. + + body disposition + A parenthesized list, consisting of a disposition type + string, followed by a parenthesized list of disposition + attribute/value pairs as defined in [DISPOSITION]. + + body language + A string or parenthesized list giving the body language + value as defined in [LANGUAGE-TAGS]. + + body location + A string list giving the body content URI as defined in + [LOCATION]. + + Any following extension data are not yet defined in this + version of the protocol. Such extension data can consist of + zero or more NILs, strings, numbers, or potentially nested + parenthesized lists of such data. Client implementations that + do a BODYSTRUCTURE fetch MUST be prepared to accept such + extension data. Server implementations MUST NOT send such + extension data until it has been defined by a revision of this + protocol. + + The basic fields of a non-multipart body part are in the + following order: + + body type + A string giving the content media type name as defined in + [MIME-IMB]. + + + + + +Crispin Standards Track [Page 75] + +RFC 3501 IMAPv4 March 2003 + + + body subtype + A string giving the content subtype name as defined in + [MIME-IMB]. + + body parameter parenthesized list + A parenthesized list of attribute/value pairs [e.g., ("foo" + "bar" "baz" "rag") where "bar" is the value of "foo" and + "rag" is the value of "baz"] as defined in [MIME-IMB]. + + body id + A string giving the content id as defined in [MIME-IMB]. + + body description + A string giving the content description as defined in + [MIME-IMB]. + + body encoding + A string giving the content transfer encoding as defined in + [MIME-IMB]. + + body size + A number giving the size of the body in octets. Note that + this size is the size in its transfer encoding and not the + resulting size after any decoding. + + A body type of type MESSAGE and subtype RFC822 contains, + immediately after the basic fields, the envelope structure, + body structure, and size in text lines of the encapsulated + message. + + A body type of type TEXT contains, immediately after the basic + fields, the size of the body in text lines. Note that this + size is the size in its content transfer encoding and not the + resulting size after any decoding. + + Extension data follows the basic fields and the type-specific + fields listed above. Extension data is never returned with the + BODY fetch, but can be returned with a BODYSTRUCTURE fetch. + Extension data, if present, MUST be in the defined order. + + The extension data of a non-multipart body part are in the + following order: + + body MD5 + A string giving the body MD5 value as defined in [MD5]. + + + + + + +Crispin Standards Track [Page 76] + +RFC 3501 IMAPv4 March 2003 + + + body disposition + A parenthesized list with the same content and function as + the body disposition for a multipart body part. + + body language + A string or parenthesized list giving the body language + value as defined in [LANGUAGE-TAGS]. + + body location + A string list giving the body content URI as defined in + [LOCATION]. + + Any following extension data are not yet defined in this + version of the protocol, and would be as described above under + multipart extension data. + + ENVELOPE + A parenthesized list that describes the envelope structure of a + message. This is computed by the server by parsing the + [RFC-2822] header into the component parts, defaulting various + fields as necessary. + + The fields of the envelope structure are in the following + order: date, subject, from, sender, reply-to, to, cc, bcc, + in-reply-to, and message-id. The date, subject, in-reply-to, + and message-id fields are strings. The from, sender, reply-to, + to, cc, and bcc fields are parenthesized lists of address + structures. + + An address structure is a parenthesized list that describes an + electronic mail address. The fields of an address structure + are in the following order: personal name, [SMTP] + at-domain-list (source route), mailbox name, and host name. + + [RFC-2822] group syntax is indicated by a special form of + address structure in which the host name field is NIL. If the + mailbox name field is also NIL, this is an end of group marker + (semi-colon in RFC 822 syntax). If the mailbox name field is + non-NIL, this is a start of group marker, and the mailbox name + field holds the group name phrase. + + If the Date, Subject, In-Reply-To, and Message-ID header lines + are absent in the [RFC-2822] header, the corresponding member + of the envelope is NIL; if these header lines are present but + empty the corresponding member of the envelope is the empty + string. + + + + + +Crispin Standards Track [Page 77] + +RFC 3501 IMAPv4 March 2003 + + + Note: some servers may return a NIL envelope member in the + "present but empty" case. Clients SHOULD treat NIL and + empty string as identical. + + Note: [RFC-2822] requires that all messages have a valid + Date header. Therefore, the date member in the envelope can + not be NIL or the empty string. + + Note: [RFC-2822] requires that the In-Reply-To and + Message-ID headers, if present, have non-empty content. + Therefore, the in-reply-to and message-id members in the + envelope can not be the empty string. + + If the From, To, cc, and bcc header lines are absent in the + [RFC-2822] header, or are present but empty, the corresponding + member of the envelope is NIL. + + If the Sender or Reply-To lines are absent in the [RFC-2822] + header, or are present but empty, the server sets the + corresponding member of the envelope to be the same value as + the from member (the client is not expected to know to do + this). + + Note: [RFC-2822] requires that all messages have a valid + From header. Therefore, the from, sender, and reply-to + members in the envelope can not be NIL. + + FLAGS + A parenthesized list of flags that are set for this message. + + INTERNALDATE + A string representing the internal date of the message. + + RFC822 + Equivalent to BODY[]. + + RFC822.HEADER + Equivalent to BODY[HEADER]. Note that this did not result in + \Seen being set, because RFC822.HEADER response data occurs as + a result of a FETCH of RFC822.HEADER. BODY[HEADER] response + data occurs as a result of a FETCH of BODY[HEADER] (which sets + \Seen) or BODY.PEEK[HEADER] (which does not set \Seen). + + RFC822.SIZE + A number expressing the [RFC-2822] size of the message. + + + + + + +Crispin Standards Track [Page 78] + +RFC 3501 IMAPv4 March 2003 + + + RFC822.TEXT + Equivalent to BODY[TEXT]. + + UID + A number expressing the unique identifier of the message. + + + Example: S: * 23 FETCH (FLAGS (\Seen) RFC822.SIZE 44827) + + +7.5. Server Responses - Command Continuation Request + + The command continuation request response is indicated by a "+" token + instead of a tag. This form of response indicates that the server is + ready to accept the continuation of a command from the client. The + remainder of this response is a line of text. + + This response is used in the AUTHENTICATE command to transmit server + data to the client, and request additional client data. This + response is also used if an argument to any command is a literal. + + The client is not permitted to send the octets of the literal unless + the server indicates that it is expected. This permits the server to + process commands and reject errors on a line-by-line basis. The + remainder of the command, including the CRLF that terminates a + command, follows the octets of the literal. If there are any + additional command arguments, the literal octets are followed by a + space and those arguments. + + Example: C: A001 LOGIN {11} + S: + Ready for additional command text + C: FRED FOOBAR {7} + S: + Ready for additional command text + C: fat man + S: A001 OK LOGIN completed + C: A044 BLURDYBLOOP {102856} + S: A044 BAD No such command as "BLURDYBLOOP" + + + + + + + + + + + + + + +Crispin Standards Track [Page 79] + +RFC 3501 IMAPv4 March 2003 + + +8. Sample IMAP4rev1 connection + + The following is a transcript of an IMAP4rev1 connection. A long + line in this sample is broken for editorial clarity. + +S: * OK IMAP4rev1 Service Ready +C: a001 login mrc secret +S: a001 OK LOGIN completed +C: a002 select inbox +S: * 18 EXISTS +S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) +S: * 2 RECENT +S: * OK [UNSEEN 17] Message 17 is the first unseen message +S: * OK [UIDVALIDITY 3857529045] UIDs valid +S: a002 OK [READ-WRITE] SELECT completed +C: a003 fetch 12 full +S: * 12 FETCH (FLAGS (\Seen) INTERNALDATE "17-Jul-1996 02:44:25 -0700" + RFC822.SIZE 4286 ENVELOPE ("Wed, 17 Jul 1996 02:23:25 -0700 (PDT)" + "IMAP4rev1 WG mtg summary and minutes" + (("Terry Gray" NIL "gray" "cac.washington.edu")) + (("Terry Gray" NIL "gray" "cac.washington.edu")) + (("Terry Gray" NIL "gray" "cac.washington.edu")) + ((NIL NIL "imap" "cac.washington.edu")) + ((NIL NIL "minutes" "CNRI.Reston.VA.US") + ("John Klensin" NIL "KLENSIN" "MIT.EDU")) NIL NIL + "<B27397-0100000@cac.washington.edu>") + BODY ("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 3028 + 92)) +S: a003 OK FETCH completed +C: a004 fetch 12 body[header] +S: * 12 FETCH (BODY[HEADER] {342} +S: Date: Wed, 17 Jul 1996 02:23:25 -0700 (PDT) +S: From: Terry Gray <gray@cac.washington.edu> +S: Subject: IMAP4rev1 WG mtg summary and minutes +S: To: imap@cac.washington.edu +S: cc: minutes@CNRI.Reston.VA.US, John Klensin <KLENSIN@MIT.EDU> +S: Message-Id: <B27397-0100000@cac.washington.edu> +S: MIME-Version: 1.0 +S: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII +S: +S: ) +S: a004 OK FETCH completed +C: a005 store 12 +flags \deleted +S: * 12 FETCH (FLAGS (\Seen \Deleted)) +S: a005 OK +FLAGS completed +C: a006 logout +S: * BYE IMAP4rev1 server terminating connection +S: a006 OK LOGOUT completed + + + +Crispin Standards Track [Page 80] + +RFC 3501 IMAPv4 March 2003 + + +9. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [ABNF]. + + In the case of alternative or optional rules in which a later rule + overlaps an earlier rule, the rule which is listed earlier MUST take + priority. For example, "\Seen" when parsed as a flag is the \Seen + flag name and not a flag-extension, even though "\Seen" can be parsed + as a flag-extension. Some, but not all, instances of this rule are + noted below. + + Note: [ABNF] rules MUST be followed strictly; in + particular: + + (1) Except as noted otherwise, all alphabetic characters + are case-insensitive. The use of upper or lower case + characters to define token strings is for editorial clarity + only. Implementations MUST accept these strings in a + case-insensitive fashion. + + (2) In all cases, SP refers to exactly one space. It is + NOT permitted to substitute TAB, insert additional spaces, + or otherwise treat SP as being equivalent to LWSP. + + (3) The ASCII NUL character, %x00, MUST NOT be used at any + time. + +address = "(" addr-name SP addr-adl SP addr-mailbox SP + addr-host ")" + +addr-adl = nstring + ; Holds route from [RFC-2822] route-addr if + ; non-NIL + +addr-host = nstring + ; NIL indicates [RFC-2822] group syntax. + ; Otherwise, holds [RFC-2822] domain name + +addr-mailbox = nstring + ; NIL indicates end of [RFC-2822] group; if + ; non-NIL and addr-host is NIL, holds + ; [RFC-2822] group name. + ; Otherwise, holds [RFC-2822] local-part + ; after removing [RFC-2822] quoting + + + + + + +Crispin Standards Track [Page 81] + +RFC 3501 IMAPv4 March 2003 + + +addr-name = nstring + ; If non-NIL, holds phrase from [RFC-2822] + ; mailbox after removing [RFC-2822] quoting + +append = "APPEND" SP mailbox [SP flag-list] [SP date-time] SP + literal + +astring = 1*ASTRING-CHAR / string + +ASTRING-CHAR = ATOM-CHAR / resp-specials + +atom = 1*ATOM-CHAR + +ATOM-CHAR = <any CHAR except atom-specials> + +atom-specials = "(" / ")" / "{" / SP / CTL / list-wildcards / + quoted-specials / resp-specials + +authenticate = "AUTHENTICATE" SP auth-type *(CRLF base64) + +auth-type = atom + ; Defined by [SASL] + +base64 = *(4base64-char) [base64-terminal] + +base64-char = ALPHA / DIGIT / "+" / "/" + ; Case-sensitive + +base64-terminal = (2base64-char "==") / (3base64-char "=") + +body = "(" (body-type-1part / body-type-mpart) ")" + +body-extension = nstring / number / + "(" body-extension *(SP body-extension) ")" + ; Future expansion. Client implementations + ; MUST accept body-extension fields. Server + ; implementations MUST NOT generate + ; body-extension fields except as defined by + ; future standard or standards-track + ; revisions of this specification. + +body-ext-1part = body-fld-md5 [SP body-fld-dsp [SP body-fld-lang + [SP body-fld-loc *(SP body-extension)]]] + ; MUST NOT be returned on non-extensible + ; "BODY" fetch + + + + + + +Crispin Standards Track [Page 82] + +RFC 3501 IMAPv4 March 2003 + + +body-ext-mpart = body-fld-param [SP body-fld-dsp [SP body-fld-lang + [SP body-fld-loc *(SP body-extension)]]] + ; MUST NOT be returned on non-extensible + ; "BODY" fetch + +body-fields = body-fld-param SP body-fld-id SP body-fld-desc SP + body-fld-enc SP body-fld-octets + +body-fld-desc = nstring + +body-fld-dsp = "(" string SP body-fld-param ")" / nil + +body-fld-enc = (DQUOTE ("7BIT" / "8BIT" / "BINARY" / "BASE64"/ + "QUOTED-PRINTABLE") DQUOTE) / string + +body-fld-id = nstring + +body-fld-lang = nstring / "(" string *(SP string) ")" + +body-fld-loc = nstring + +body-fld-lines = number + +body-fld-md5 = nstring + +body-fld-octets = number + +body-fld-param = "(" string SP string *(SP string SP string) ")" / nil + +body-type-1part = (body-type-basic / body-type-msg / body-type-text) + [SP body-ext-1part] + +body-type-basic = media-basic SP body-fields + ; MESSAGE subtype MUST NOT be "RFC822" + +body-type-mpart = 1*body SP media-subtype + [SP body-ext-mpart] + +body-type-msg = media-message SP body-fields SP envelope + SP body SP body-fld-lines + +body-type-text = media-text SP body-fields SP body-fld-lines + +capability = ("AUTH=" auth-type) / atom + ; New capabilities MUST begin with "X" or be + ; registered with IANA as standard or + ; standards-track + + + + +Crispin Standards Track [Page 83] + +RFC 3501 IMAPv4 March 2003 + + +capability-data = "CAPABILITY" *(SP capability) SP "IMAP4rev1" + *(SP capability) + ; Servers MUST implement the STARTTLS, AUTH=PLAIN, + ; and LOGINDISABLED capabilities + ; Servers which offer RFC 1730 compatibility MUST + ; list "IMAP4" as the first capability. + +CHAR8 = %x01-ff + ; any OCTET except NUL, %x00 + +command = tag SP (command-any / command-auth / command-nonauth / + command-select) CRLF + ; Modal based on state + +command-any = "CAPABILITY" / "LOGOUT" / "NOOP" / x-command + ; Valid in all states + +command-auth = append / create / delete / examine / list / lsub / + rename / select / status / subscribe / unsubscribe + ; Valid only in Authenticated or Selected state + +command-nonauth = login / authenticate / "STARTTLS" + ; Valid only when in Not Authenticated state + +command-select = "CHECK" / "CLOSE" / "EXPUNGE" / copy / fetch / store / + uid / search + ; Valid only when in Selected state + +continue-req = "+" SP (resp-text / base64) CRLF + +copy = "COPY" SP sequence-set SP mailbox + +create = "CREATE" SP mailbox + ; Use of INBOX gives a NO error + +date = date-text / DQUOTE date-text DQUOTE + +date-day = 1*2DIGIT + ; Day of month + +date-day-fixed = (SP DIGIT) / 2DIGIT + ; Fixed-format version of date-day + +date-month = "Jan" / "Feb" / "Mar" / "Apr" / "May" / "Jun" / + "Jul" / "Aug" / "Sep" / "Oct" / "Nov" / "Dec" + +date-text = date-day "-" date-month "-" date-year + + + + +Crispin Standards Track [Page 84] + +RFC 3501 IMAPv4 March 2003 + + +date-year = 4DIGIT + +date-time = DQUOTE date-day-fixed "-" date-month "-" date-year + SP time SP zone DQUOTE + +delete = "DELETE" SP mailbox + ; Use of INBOX gives a NO error + +digit-nz = %x31-39 + ; 1-9 + +envelope = "(" env-date SP env-subject SP env-from SP + env-sender SP env-reply-to SP env-to SP env-cc SP + env-bcc SP env-in-reply-to SP env-message-id ")" + +env-bcc = "(" 1*address ")" / nil + +env-cc = "(" 1*address ")" / nil + +env-date = nstring + +env-from = "(" 1*address ")" / nil + +env-in-reply-to = nstring + +env-message-id = nstring + +env-reply-to = "(" 1*address ")" / nil + +env-sender = "(" 1*address ")" / nil + +env-subject = nstring + +env-to = "(" 1*address ")" / nil + +examine = "EXAMINE" SP mailbox + +fetch = "FETCH" SP sequence-set SP ("ALL" / "FULL" / "FAST" / + fetch-att / "(" fetch-att *(SP fetch-att) ")") + +fetch-att = "ENVELOPE" / "FLAGS" / "INTERNALDATE" / + "RFC822" [".HEADER" / ".SIZE" / ".TEXT"] / + "BODY" ["STRUCTURE"] / "UID" / + "BODY" section ["<" number "." nz-number ">"] / + "BODY.PEEK" section ["<" number "." nz-number ">"] + + + + + + +Crispin Standards Track [Page 85] + +RFC 3501 IMAPv4 March 2003 + + +flag = "\Answered" / "\Flagged" / "\Deleted" / + "\Seen" / "\Draft" / flag-keyword / flag-extension + ; Does not include "\Recent" + +flag-extension = "\" atom + ; Future expansion. Client implementations + ; MUST accept flag-extension flags. Server + ; implementations MUST NOT generate + ; flag-extension flags except as defined by + ; future standard or standards-track + ; revisions of this specification. + +flag-fetch = flag / "\Recent" + +flag-keyword = atom + +flag-list = "(" [flag *(SP flag)] ")" + +flag-perm = flag / "\*" + +greeting = "*" SP (resp-cond-auth / resp-cond-bye) CRLF + +header-fld-name = astring + +header-list = "(" header-fld-name *(SP header-fld-name) ")" + +list = "LIST" SP mailbox SP list-mailbox + +list-mailbox = 1*list-char / string + +list-char = ATOM-CHAR / list-wildcards / resp-specials + +list-wildcards = "%" / "*" + +literal = "{" number "}" CRLF *CHAR8 + ; Number represents the number of CHAR8s + +login = "LOGIN" SP userid SP password + +lsub = "LSUB" SP mailbox SP list-mailbox + + + + + + + + + + + +Crispin Standards Track [Page 86] + +RFC 3501 IMAPv4 March 2003 + + +mailbox = "INBOX" / astring + ; INBOX is case-insensitive. All case variants of + ; INBOX (e.g., "iNbOx") MUST be interpreted as INBOX + ; not as an astring. An astring which consists of + ; the case-insensitive sequence "I" "N" "B" "O" "X" + ; is considered to be INBOX and not an astring. + ; Refer to section 5.1 for further + ; semantic details of mailbox names. + +mailbox-data = "FLAGS" SP flag-list / "LIST" SP mailbox-list / + "LSUB" SP mailbox-list / "SEARCH" *(SP nz-number) / + "STATUS" SP mailbox SP "(" [status-att-list] ")" / + number SP "EXISTS" / number SP "RECENT" + +mailbox-list = "(" [mbx-list-flags] ")" SP + (DQUOTE QUOTED-CHAR DQUOTE / nil) SP mailbox + +mbx-list-flags = *(mbx-list-oflag SP) mbx-list-sflag + *(SP mbx-list-oflag) / + mbx-list-oflag *(SP mbx-list-oflag) + +mbx-list-oflag = "\Noinferiors" / flag-extension + ; Other flags; multiple possible per LIST response + +mbx-list-sflag = "\Noselect" / "\Marked" / "\Unmarked" + ; Selectability flags; only one per LIST response + +media-basic = ((DQUOTE ("APPLICATION" / "AUDIO" / "IMAGE" / + "MESSAGE" / "VIDEO") DQUOTE) / string) SP + media-subtype + ; Defined in [MIME-IMT] + +media-message = DQUOTE "MESSAGE" DQUOTE SP DQUOTE "RFC822" DQUOTE + ; Defined in [MIME-IMT] + +media-subtype = string + ; Defined in [MIME-IMT] + +media-text = DQUOTE "TEXT" DQUOTE SP media-subtype + ; Defined in [MIME-IMT] + +message-data = nz-number SP ("EXPUNGE" / ("FETCH" SP msg-att)) + +msg-att = "(" (msg-att-dynamic / msg-att-static) + *(SP (msg-att-dynamic / msg-att-static)) ")" + +msg-att-dynamic = "FLAGS" SP "(" [flag-fetch *(SP flag-fetch)] ")" + ; MAY change for a message + + + +Crispin Standards Track [Page 87] + +RFC 3501 IMAPv4 March 2003 + + +msg-att-static = "ENVELOPE" SP envelope / "INTERNALDATE" SP date-time / + "RFC822" [".HEADER" / ".TEXT"] SP nstring / + "RFC822.SIZE" SP number / + "BODY" ["STRUCTURE"] SP body / + "BODY" section ["<" number ">"] SP nstring / + "UID" SP uniqueid + ; MUST NOT change for a message + +nil = "NIL" + +nstring = string / nil + +number = 1*DIGIT + ; Unsigned 32-bit integer + ; (0 <= n < 4,294,967,296) + +nz-number = digit-nz *DIGIT + ; Non-zero unsigned 32-bit integer + ; (0 < n < 4,294,967,296) + +password = astring + +quoted = DQUOTE *QUOTED-CHAR DQUOTE + +QUOTED-CHAR = <any TEXT-CHAR except quoted-specials> / + "\" quoted-specials + +quoted-specials = DQUOTE / "\" + +rename = "RENAME" SP mailbox SP mailbox + ; Use of INBOX as a destination gives a NO error + +response = *(continue-req / response-data) response-done + +response-data = "*" SP (resp-cond-state / resp-cond-bye / + mailbox-data / message-data / capability-data) CRLF + +response-done = response-tagged / response-fatal + +response-fatal = "*" SP resp-cond-bye CRLF + ; Server closes connection immediately + +response-tagged = tag SP resp-cond-state CRLF + +resp-cond-auth = ("OK" / "PREAUTH") SP resp-text + ; Authentication condition + + + + + +Crispin Standards Track [Page 88] + +RFC 3501 IMAPv4 March 2003 + + +resp-cond-bye = "BYE" SP resp-text + +resp-cond-state = ("OK" / "NO" / "BAD") SP resp-text + ; Status condition + +resp-specials = "]" + +resp-text = ["[" resp-text-code "]" SP] text + +resp-text-code = "ALERT" / + "BADCHARSET" [SP "(" astring *(SP astring) ")" ] / + capability-data / "PARSE" / + "PERMANENTFLAGS" SP "(" + [flag-perm *(SP flag-perm)] ")" / + "READ-ONLY" / "READ-WRITE" / "TRYCREATE" / + "UIDNEXT" SP nz-number / "UIDVALIDITY" SP nz-number / + "UNSEEN" SP nz-number / + atom [SP 1*<any TEXT-CHAR except "]">] + +search = "SEARCH" [SP "CHARSET" SP astring] 1*(SP search-key) + ; CHARSET argument to MUST be registered with IANA + +search-key = "ALL" / "ANSWERED" / "BCC" SP astring / + "BEFORE" SP date / "BODY" SP astring / + "CC" SP astring / "DELETED" / "FLAGGED" / + "FROM" SP astring / "KEYWORD" SP flag-keyword / + "NEW" / "OLD" / "ON" SP date / "RECENT" / "SEEN" / + "SINCE" SP date / "SUBJECT" SP astring / + "TEXT" SP astring / "TO" SP astring / + "UNANSWERED" / "UNDELETED" / "UNFLAGGED" / + "UNKEYWORD" SP flag-keyword / "UNSEEN" / + ; Above this line were in [IMAP2] + "DRAFT" / "HEADER" SP header-fld-name SP astring / + "LARGER" SP number / "NOT" SP search-key / + "OR" SP search-key SP search-key / + "SENTBEFORE" SP date / "SENTON" SP date / + "SENTSINCE" SP date / "SMALLER" SP number / + "UID" SP sequence-set / "UNDRAFT" / sequence-set / + "(" search-key *(SP search-key) ")" + +section = "[" [section-spec] "]" + +section-msgtext = "HEADER" / "HEADER.FIELDS" [".NOT"] SP header-list / + "TEXT" + ; top-level or MESSAGE/RFC822 part + +section-part = nz-number *("." nz-number) + ; body part nesting + + + +Crispin Standards Track [Page 89] + +RFC 3501 IMAPv4 March 2003 + + +section-spec = section-msgtext / (section-part ["." section-text]) + +section-text = section-msgtext / "MIME" + ; text other than actual body part (headers, etc.) + +select = "SELECT" SP mailbox + +seq-number = nz-number / "*" + ; message sequence number (COPY, FETCH, STORE + ; commands) or unique identifier (UID COPY, + ; UID FETCH, UID STORE commands). + ; * represents the largest number in use. In + ; the case of message sequence numbers, it is + ; the number of messages in a non-empty mailbox. + ; In the case of unique identifiers, it is the + ; unique identifier of the last message in the + ; mailbox or, if the mailbox is empty, the + ; mailbox's current UIDNEXT value. + ; The server should respond with a tagged BAD + ; response to a command that uses a message + ; sequence number greater than the number of + ; messages in the selected mailbox. This + ; includes "*" if the selected mailbox is empty. + +seq-range = seq-number ":" seq-number + ; two seq-number values and all values between + ; these two regardless of order. + ; Example: 2:4 and 4:2 are equivalent and indicate + ; values 2, 3, and 4. + ; Example: a unique identifer sequence range of + ; 3291:* includes the UID of the last message in + ; the mailbox, even if that value is less than 3291. + +sequence-set = (seq-number / seq-range) *("," sequence-set) + ; set of seq-number values, regardless of order. + ; Servers MAY coalesce overlaps and/or execute the + ; sequence in any order. + ; Example: a message sequence number set of + ; 2,4:7,9,12:* for a mailbox with 15 messages is + ; equivalent to 2,4,5,6,7,9,12,13,14,15 + ; Example: a message sequence number set of *:4,5:7 + ; for a mailbox with 10 messages is equivalent to + ; 10,9,8,7,6,5,4,5,6,7 and MAY be reordered and + ; overlap coalesced to be 4,5,6,7,8,9,10. + +status = "STATUS" SP mailbox SP + "(" status-att *(SP status-att) ")" + + + + +Crispin Standards Track [Page 90] + +RFC 3501 IMAPv4 March 2003 + + +status-att = "MESSAGES" / "RECENT" / "UIDNEXT" / "UIDVALIDITY" / + "UNSEEN" + +status-att-list = status-att SP number *(SP status-att SP number) + +store = "STORE" SP sequence-set SP store-att-flags + +store-att-flags = (["+" / "-"] "FLAGS" [".SILENT"]) SP + (flag-list / (flag *(SP flag))) + +string = quoted / literal + +subscribe = "SUBSCRIBE" SP mailbox + +tag = 1*<any ASTRING-CHAR except "+"> + +text = 1*TEXT-CHAR + +TEXT-CHAR = <any CHAR except CR and LF> + +time = 2DIGIT ":" 2DIGIT ":" 2DIGIT + ; Hours minutes seconds + +uid = "UID" SP (copy / fetch / search / store) + ; Unique identifiers used instead of message + ; sequence numbers + +uniqueid = nz-number + ; Strictly ascending + +unsubscribe = "UNSUBSCRIBE" SP mailbox + +userid = astring + +x-command = "X" atom <experimental command arguments> + +zone = ("+" / "-") 4DIGIT + ; Signed four-digit value of hhmm representing + ; hours and minutes east of Greenwich (that is, + ; the amount that the given time differs from + ; Universal Time). Subtracting the timezone + ; from the given time will give the UT form. + ; The Universal Time zone is "+0000". + + + + + + + + +Crispin Standards Track [Page 91] + +RFC 3501 IMAPv4 March 2003 + + +10. Author's Note + + This document is a revision or rewrite of earlier documents, and + supercedes the protocol specification in those documents: RFC 2060, + RFC 1730, unpublished IMAP2bis.TXT document, RFC 1176, and RFC 1064. + +11. Security Considerations + + IMAP4rev1 protocol transactions, including electronic mail data, are + sent in the clear over the network unless protection from snooping is + negotiated. This can be accomplished either by the use of STARTTLS, + negotiated privacy protection in the AUTHENTICATE command, or some + other protection mechanism. + +11.1. STARTTLS Security Considerations + + The specification of the STARTTLS command and LOGINDISABLED + capability in this document replaces that in [IMAP-TLS]. [IMAP-TLS] + remains normative for the PLAIN [SASL] authenticator. + + IMAP client and server implementations MUST implement the + TLS_RSA_WITH_RC4_128_MD5 [TLS] cipher suite, and SHOULD implement the + TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA [TLS] cipher suite. This is + important as it assures that any two compliant implementations can be + configured to interoperate. All other cipher suites are OPTIONAL. + Note that this is a change from section 2.1 of [IMAP-TLS]. + + During the [TLS] negotiation, the client MUST check its understanding + of the server hostname against the server's identity as presented in + the server Certificate message, in order to prevent man-in-the-middle + attacks. If the match fails, the client SHOULD either ask for + explicit user confirmation, or terminate the connection and indicate + that the server's identity is suspect. Matching is performed + according to these rules: + + The client MUST use the server hostname it used to open the + connection as the value to compare against the server name + as expressed in the server certificate. The client MUST + NOT use any form of the server hostname derived from an + insecure remote source (e.g., insecure DNS lookup). CNAME + canonicalization is not done. + + If a subjectAltName extension of type dNSName is present in + the certificate, it SHOULD be used as the source of the + server's identity. + + Matching is case-insensitive. + + + + +Crispin Standards Track [Page 92] + +RFC 3501 IMAPv4 March 2003 + + + A "*" wildcard character MAY be used as the left-most name + component in the certificate. For example, *.example.com + would match a.example.com, foo.example.com, etc. but would + not match example.com. + + If the certificate contains multiple names (e.g., more than + one dNSName field), then a match with any one of the fields + is considered acceptable. + + Both the client and server MUST check the result of the STARTTLS + command and subsequent [TLS] negotiation to see whether acceptable + authentication or privacy was achieved. + +11.2. Other Security Considerations + + A server error message for an AUTHENTICATE command which fails due to + invalid credentials SHOULD NOT detail why the credentials are + invalid. + + Use of the LOGIN command sends passwords in the clear. This can be + avoided by using the AUTHENTICATE command with a [SASL] mechanism + that does not use plaintext passwords, by first negotiating + encryption via STARTTLS or some other protection mechanism. + + A server implementation MUST implement a configuration that, at the + time of authentication, requires: + (1) The STARTTLS command has been negotiated. + OR + (2) Some other mechanism that protects the session from password + snooping has been provided. + OR + (3) The following measures are in place: + (a) The LOGINDISABLED capability is advertised, and [SASL] + mechanisms (such as PLAIN) using plaintext passwords are NOT + advertised in the CAPABILITY list. + AND + (b) The LOGIN command returns an error even if the password is + correct. + AND + (c) The AUTHENTICATE command returns an error with all [SASL] + mechanisms that use plaintext passwords, even if the password + is correct. + + A server error message for a failing LOGIN command SHOULD NOT specify + that the user name, as opposed to the password, is invalid. + + A server SHOULD have mechanisms in place to limit or delay failed + AUTHENTICATE/LOGIN attempts. + + + +Crispin Standards Track [Page 93] + +RFC 3501 IMAPv4 March 2003 + + + Additional security considerations are discussed in the section + discussing the AUTHENTICATE and LOGIN commands. + +12. IANA Considerations + + IMAP4 capabilities are registered by publishing a standards track or + IESG approved experimental RFC. The registry is currently located + at: + + http://www.iana.org/assignments/imap4-capabilities + + As this specification revises the STARTTLS and LOGINDISABLED + extensions previously defined in [IMAP-TLS], the registry will be + updated accordingly. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Crispin Standards Track [Page 94] + +RFC 3501 IMAPv4 March 2003 + + +Appendices + +A. Normative References + + The following documents contain definitions or specifications that + are necessary to understand this document properly: + [ABNF] Crocker, D. and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", RFC 2234, + November 1997. + + [ANONYMOUS] Newman, C., "Anonymous SASL Mechanism", RFC + 2245, November 1997. + + [CHARSET] Freed, N. and J. Postel, "IANA Character Set + Registration Procedures", RFC 2978, October + 2000. + + [DIGEST-MD5] Leach, P. and C. Newman, "Using Digest + Authentication as a SASL Mechanism", RFC 2831, + May 2000. + + [DISPOSITION] Troost, R., Dorner, S. and K. Moore, + "Communicating Presentation Information in + Internet Messages: The Content-Disposition + Header", RFC 2183, August 1997. + + [IMAP-TLS] Newman, C., "Using TLS with IMAP, POP3 and + ACAP", RFC 2595, June 1999. + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to + Indicate Requirement Levels", BCP 14, RFC 2119, + March 1997. + + [LANGUAGE-TAGS] Alvestrand, H., "Tags for the Identification of + Languages", BCP 47, RFC 3066, January 2001. + + [LOCATION] Palme, J., Hopmann, A. and N. Shelness, "MIME + Encapsulation of Aggregate Documents, such as + HTML (MHTML)", RFC 2557, March 1999. + + [MD5] Myers, J. and M. Rose, "The Content-MD5 Header + Field", RFC 1864, October 1995. + + + + + + + + + +Crispin Standards Track [Page 95] + +RFC 3501 IMAPv4 March 2003 + + + [MIME-HDRS] Moore, K., "MIME (Multipurpose Internet Mail + Extensions) Part Three: Message Header + Extensions for Non-ASCII Text", RFC 2047, + November 1996. + + [MIME-IMB] Freed, N. and N. Borenstein, "MIME + (Multipurpose Internet Mail Extensions) Part + One: Format of Internet Message Bodies", RFC + 2045, November 1996. + + [MIME-IMT] Freed, N. and N. Borenstein, "MIME + (Multipurpose Internet Mail Extensions) Part + Two: Media Types", RFC 2046, November 1996. + + [RFC-2822] Resnick, P., "Internet Message Format", RFC + 2822, April 2001. + + [SASL] Myers, J., "Simple Authentication and Security + Layer (SASL)", RFC 2222, October 1997. + + [TLS] Dierks, T. and C. Allen, "The TLS Protocol + Version 1.0", RFC 2246, January 1999. + + [UTF-7] Goldsmith, D. and M. Davis, "UTF-7: A Mail-Safe + Transformation Format of Unicode", RFC 2152, + May 1997. + + The following documents describe quality-of-implementation issues + that should be carefully considered when implementing this protocol: + + [IMAP-IMPLEMENTATION] Leiba, B., "IMAP Implementation + Recommendations", RFC 2683, September 1999. + + [IMAP-MULTIACCESS] Gahrns, M., "IMAP4 Multi-Accessed Mailbox + Practice", RFC 2180, July 1997. + +A.1 Informative References + + The following documents describe related protocols: + + [IMAP-DISC] Austein, R., "Synchronization Operations for + Disconnected IMAP4 Clients", Work in Progress. + + [IMAP-MODEL] Crispin, M., "Distributed Electronic Mail + Models in IMAP4", RFC 1733, December 1994. + + + + + + +Crispin Standards Track [Page 96] + +RFC 3501 IMAPv4 March 2003 + + + [ACAP] Newman, C. and J. Myers, "ACAP -- Application + Configuration Access Protocol", RFC 2244, + November 1997. + + [SMTP] Klensin, J., "Simple Mail Transfer Protocol", + STD 10, RFC 2821, April 2001. + + The following documents are historical or describe historical aspects + of this protocol: + + [IMAP-COMPAT] Crispin, M., "IMAP4 Compatibility with + IMAP2bis", RFC 2061, December 1996. + + [IMAP-HISTORICAL] Crispin, M., "IMAP4 Compatibility with IMAP2 + and IMAP2bis", RFC 1732, December 1994. + + [IMAP-OBSOLETE] Crispin, M., "Internet Message Access Protocol + - Obsolete Syntax", RFC 2062, December 1996. + + [IMAP2] Crispin, M., "Interactive Mail Access Protocol + - Version 2", RFC 1176, August 1990. + + [RFC-822] Crocker, D., "Standard for the Format of ARPA + Internet Text Messages", STD 11, RFC 822, + August 1982. + + [RFC-821] Postel, J., "Simple Mail Transfer Protocol", + STD 10, RFC 821, August 1982. + +B. Changes from RFC 2060 + + 1) Clarify description of unique identifiers and their semantics. + + 2) Fix the SELECT description to clarify that UIDVALIDITY is required + in the SELECT and EXAMINE responses. + + 3) Added an example of a failing search. + + 4) Correct store-att-flags: "#flag" should be "1#flag". + + 5) Made search and section rules clearer. + + 6) Correct the STORE example. + + 7) Correct "BASE645" misspelling. + + 8) Remove extraneous close parenthesis in example of two-part message + with text and BASE64 attachment. + + + +Crispin Standards Track [Page 97] + +RFC 3501 IMAPv4 March 2003 + + + 9) Remove obsolete "MAILBOX" response from mailbox-data. + + 10) A spurious "<" in the rule for mailbox-data was removed. + + 11) Add CRLF to continue-req. + + 12) Specifically exclude "]" from the atom in resp-text-code. + + 13) Clarify that clients and servers should adhere strictly to the + protocol syntax. + + 14) Emphasize in 5.2 that EXISTS can not be used to shrink a mailbox. + + 15) Add NEWNAME to resp-text-code. + + 16) Clarify that the empty string, not NIL, is used as arguments to + LIST. + + 17) Clarify that NIL can be returned as a hierarchy delimiter for the + empty string mailbox name argument if the mailbox namespace is flat. + + 18) Clarify that addr-mailbox and addr-name have RFC-2822 quoting + removed. + + 19) Update UTF-7 reference. + + 20) Fix example in 6.3.11. + + 21) Clarify that non-existent UIDs are ignored. + + 22) Update DISPOSITION reference. + + 23) Expand state diagram. + + 24) Clarify that partial fetch responses are only returned in + response to a partial fetch command. + + 25) Add UIDNEXT response code. Correct UIDVALIDITY definition + reference. + + 26) Further clarification of "can" vs. "MAY". + + 27) Reference RFC-2119. + + 28) Clarify that superfluous shifts are not permitted in modified + UTF-7. + + 29) Clarify that there are no implicit shifts in modified UTF-7. + + + +Crispin Standards Track [Page 98] + +RFC 3501 IMAPv4 March 2003 + + + 30) Clarify that "INBOX" in a mailbox name is always INBOX, even if + it is given as a string. + + 31) Add missing open parenthesis in media-basic grammar rule. + + 32) Correct attribute syntax in mailbox-data. + + 33) Add UIDNEXT to EXAMINE responses. + + 34) Clarify UNSEEN, PERMANENTFLAGS, UIDVALIDITY, and UIDNEXT + responses in SELECT and EXAMINE. They are required now, but weren't + in older versions. + + 35) Update references with RFC numbers. + + 36) Flush text-mime2. + + 37) Clarify that modified UTF-7 names must be case-sensitive and that + violating the convention should be avoided. + + 38) Correct UID FETCH example. + + 39) Clarify UID FETCH, UID STORE, and UID SEARCH vs. untagged EXPUNGE + responses. + + 40) Clarify the use of the word "convention". + + 41) Clarify that a command is not "in progress" until it has been + fully received (specifically, that a command is not "in progress" + during command continuation negotiation). + + 42) Clarify envelope defaulting. + + 43) Clarify that SP means one and only one space character. + + 44) Forbid silly states in LIST response. + + 45) Clarify that the ENVELOPE, INTERNALDATE, RFC822*, BODY*, and UID + for a message is static. + + 46) Add BADCHARSET response code. + + 47) Update formal syntax to [ABNF] conventions. + + 48) Clarify trailing hierarchy delimiter in CREATE semantics. + + 49) Clarify that the "blank line" is the [RFC-2822] delimiting blank + line. + + + +Crispin Standards Track [Page 99] + +RFC 3501 IMAPv4 March 2003 + + + 50) Clarify that RENAME should also create hierarchy as needed for + the command to complete. + + 51) Fix body-ext-mpart to not require language if disposition + present. + + 52) Clarify the RFC822.HEADER response. + + 53) Correct missing space after charset astring in search. + + 54) Correct missing quote for BADCHARSET in resp-text-code. + + 55) Clarify that ALL, FAST, and FULL preclude any other data items + appearing. + + 56) Clarify semantics of reference argument in LIST. + + 57) Clarify that a null string for SEARCH HEADER X-FOO means any + message with a header line with a field-name of X-FOO regardless of + the text of the header. + + 58) Specifically reserve 8-bit mailbox names for future use as UTF-8. + + 59) It is not an error for the client to store a flag that is not in + the PERMANENTFLAGS list; however, the server will either ignore the + change or make the change in the session only. + + 60) Correct/clarify the text regarding superfluous shifts. + + 61) Correct typographic errors in the "Changes" section. + + 62) Clarify that STATUS must not be used to check for new messages in + the selected mailbox + + 63) Clarify LSUB behavior with "%" wildcard. + + 64) Change AUTHORIZATION to AUTHENTICATE in section 7.5. + + 65) Clarify description of multipart body type. + + 66) Clarify that STORE FLAGS does not affect \Recent. + + 67) Change "west" to "east" in description of timezone. + + 68) Clarify that commands which break command pipelining must wait + for a completion result response. + + 69) Clarify that EXAMINE does not affect \Recent. + + + +Crispin Standards Track [Page 100] + +RFC 3501 IMAPv4 March 2003 + + + 70) Make description of MIME structure consistent. + + 71) Clarify that date searches disregard the time and timezone of the + INTERNALDATE or Date: header. In other words, "ON 13-APR-2000" means + messages with an INTERNALDATE text which starts with "13-APR-2000", + even if timezone differential from the local timezone is sufficient + to move that INTERNALDATE into the previous or next day. + + 72) Clarify that the header fetches don't add a blank line if one + isn't in the [RFC-2822] message. + + 73) Clarify (in discussion of UIDs) that messages are immutable. + + 74) Add an example of CHARSET searching. + + 75) Clarify in SEARCH that keywords are a type of flag. + + 76) Clarify the mandatory nature of the SELECT data responses. + + 77) Add optional CAPABILITY response code in the initial OK or + PREAUTH. + + 78) Add note that server can send an untagged CAPABILITY command as + part of the responses to AUTHENTICATE and LOGIN. + + 79) Remove statement about it being unnecessary to issue a CAPABILITY + command more than once in a connection. That statement is no longer + true. + + 80) Clarify that untagged EXPUNGE decrements the number of messages + in the mailbox. + + 81) Fix definition of "body" (concatenation has tighter binding than + alternation). + + 82) Add a new "Special Notes to Implementors" section with reference + to [IMAP-IMPLEMENTATION]. + + 83) Clarify that an untagged CAPABILITY response to an AUTHENTICATE + command should only be done if a security layer was not negotiated. + + 84) Change the definition of atom to exclude "]". Update astring to + include "]" for compatiblity with the past. Remove resp-text-atom. + + 85) Remove NEWNAME. It can't work because mailbox names can be + literals and can include "]". Functionality can be addressed via + referrals. + + + + +Crispin Standards Track [Page 101] + +RFC 3501 IMAPv4 March 2003 + + + 86) Move modified UTF-7 rationale in order to have more logical + paragraph flow. + + 87) Clarify UID uniqueness guarantees with the use of MUST. + + 88) Note that clients should read response data until the connection + is closed instead of immediately closing on a BYE. + + 89) Change RFC-822 references to RFC-2822. + + 90) Clarify that RFC-2822 should be followed instead of RFC-822. + + 91) Change recommendation of optional automatic capabilities in LOGIN + and AUTHENTICATE to use the CAPABILITY response code in the tagged + OK. This is more interoperable than an unsolicited untagged + CAPABILITY response. + + 92) STARTTLS and AUTH=PLAIN are mandatory to implement; add + recommendations for other [SASL] mechanisms. + + 93) Clarify that a "connection" (as opposed to "server" or "command") + is in one of the four states. + + 94) Clarify that a failed or rejected command does not change state. + + 95) Split references between normative and informative. + + 96) Discuss authentication failure issues in security section. + + 97) Clarify that a data item is not necessarily of only one data + type. + + 98) Clarify that sequence ranges are independent of order. + + 99) Change an example to clarify that superfluous shifts in + Modified-UTF7 can not be fixed just by omitting the shift. The + entire string must be recalculated. + + 100) Change Envelope Structure definition since [RFC-2822] uses + "envelope" to refer to the [SMTP] envelope and not the envelope data + that appears in the [RFC-2822] header. + + 101) Expand on RFC822.HEADER response data vs. BODY[HEADER]. + + 102) Clarify Logout state semantics, change ASCII art. + + 103) Security changes to comply with IESG requirements. + + + + +Crispin Standards Track [Page 102] + +RFC 3501 IMAPv4 March 2003 + + + 104) Add definition for body URI. + + 105) Break sequence range definition into three rules, with rewritten + descriptions for each. + + 106) Move STARTTLS and LOGINDISABLED here from [IMAP-TLS]. + + 107) Add IANA Considerations section. + + 108) Clarify valid client assumptions for new message UIDs vs. + UIDNEXT. + + 109) Clarify that changes to permanentflags affect concurrent + sessions as well as subsequent sessions. + + 110) Clarify that authenticated state can be entered by the CLOSE + command. + + 111) Emphasize that SELECT and EXAMINE are the exceptions to the rule + that a failing command does not change state. + + 112) Clarify that newly-appended messages have the Recent flag set. + + 113) Clarify that newly-copied messages SHOULD have the Recent flag + set. + + 114) Clarify that UID commands always return the UID in FETCH + responses. + +C. Key Word Index + + +FLAGS <flag list> (store command data item) ............... 59 + +FLAGS.SILENT <flag list> (store command data item) ........ 59 + -FLAGS <flag list> (store command data item) ............... 59 + -FLAGS.SILENT <flag list> (store command data item) ........ 59 + ALERT (response code) ...................................... 64 + ALL (fetch item) ........................................... 55 + ALL (search key) ........................................... 50 + ANSWERED (search key) ...................................... 50 + APPEND (command) ........................................... 45 + AUTHENTICATE (command) ..................................... 27 + BAD (response) ............................................. 66 + BADCHARSET (response code) ................................. 64 + BCC <string> (search key) .................................. 51 + BEFORE <date> (search key) ................................. 51 + BODY (fetch item) .......................................... 55 + BODY (fetch result) ........................................ 73 + BODY <string> (search key) ................................. 51 + + + +Crispin Standards Track [Page 103] + +RFC 3501 IMAPv4 March 2003 + + + BODY.PEEK[<section>]<<partial>> (fetch item) ............... 57 + BODYSTRUCTURE (fetch item) ................................. 57 + BODYSTRUCTURE (fetch result) ............................... 74 + BODY[<section>]<<origin octet>> (fetch result) ............. 74 + BODY[<section>]<<partial>> (fetch item) .................... 55 + BYE (response) ............................................. 67 + Body Structure (message attribute) ......................... 12 + CAPABILITY (command) ....................................... 24 + CAPABILITY (response code) ................................. 64 + CAPABILITY (response) ...................................... 68 + CC <string> (search key) ................................... 51 + CHECK (command) ............................................ 47 + CLOSE (command) ............................................ 48 + COPY (command) ............................................. 59 + CREATE (command) ........................................... 34 + DELETE (command) ........................................... 35 + DELETED (search key) ....................................... 51 + DRAFT (search key) ......................................... 51 + ENVELOPE (fetch item) ...................................... 57 + ENVELOPE (fetch result) .................................... 77 + EXAMINE (command) .......................................... 33 + EXISTS (response) .......................................... 71 + EXPUNGE (command) .......................................... 48 + EXPUNGE (response) ......................................... 72 + Envelope Structure (message attribute) ..................... 12 + FAST (fetch item) .......................................... 55 + FETCH (command) ............................................ 54 + FETCH (response) ........................................... 73 + FLAGGED (search key) ....................................... 51 + FLAGS (fetch item) ......................................... 57 + FLAGS (fetch result) ....................................... 78 + FLAGS (response) ........................................... 71 + FLAGS <flag list> (store command data item) ................ 59 + FLAGS.SILENT <flag list> (store command data item) ......... 59 + FROM <string> (search key) ................................. 51 + FULL (fetch item) .......................................... 55 + Flags (message attribute) .................................. 11 + HEADER (part specifier) .................................... 55 + HEADER <field-name> <string> (search key) .................. 51 + HEADER.FIELDS <header-list> (part specifier) ............... 55 + HEADER.FIELDS.NOT <header-list> (part specifier) ........... 55 + INTERNALDATE (fetch item) .................................. 57 + INTERNALDATE (fetch result) ................................ 78 + Internal Date (message attribute) .......................... 12 + KEYWORD <flag> (search key) ................................ 51 + Keyword (type of flag) ..................................... 11 + LARGER <n> (search key) .................................... 51 + LIST (command) ............................................. 40 + + + +Crispin Standards Track [Page 104] + +RFC 3501 IMAPv4 March 2003 + + + LIST (response) ............................................ 69 + LOGIN (command) ............................................ 30 + LOGOUT (command) ........................................... 25 + LSUB (command) ............................................. 43 + LSUB (response) ............................................ 70 + MAY (specification requirement term) ....................... 4 + MESSAGES (status item) ..................................... 45 + MIME (part specifier) ...................................... 56 + MUST (specification requirement term) ...................... 4 + MUST NOT (specification requirement term) .................. 4 + Message Sequence Number (message attribute) ................ 10 + NEW (search key) ........................................... 51 + NO (response) .............................................. 66 + NOOP (command) ............................................. 25 + NOT <search-key> (search key) .............................. 52 + OK (response) .............................................. 65 + OLD (search key) ........................................... 52 + ON <date> (search key) ..................................... 52 + OPTIONAL (specification requirement term) .................. 4 + OR <search-key1> <search-key2> (search key) ................ 52 + PARSE (response code) ...................................... 64 + PERMANENTFLAGS (response code) ............................. 64 + PREAUTH (response) ......................................... 67 + Permanent Flag (class of flag) ............................. 12 + READ-ONLY (response code) .................................. 65 + READ-WRITE (response code) ................................. 65 + RECENT (response) .......................................... 72 + RECENT (search key) ........................................ 52 + RECENT (status item) ....................................... 45 + RENAME (command) ........................................... 37 + REQUIRED (specification requirement term) .................. 4 + RFC822 (fetch item) ........................................ 57 + RFC822 (fetch result) ...................................... 78 + RFC822.HEADER (fetch item) ................................. 57 + RFC822.HEADER (fetch result) ............................... 78 + RFC822.SIZE (fetch item) ................................... 57 + RFC822.SIZE (fetch result) ................................. 78 + RFC822.TEXT (fetch item) ................................... 58 + RFC822.TEXT (fetch result) ................................. 79 + SEARCH (command) ........................................... 49 + SEARCH (response) .......................................... 71 + SEEN (search key) .......................................... 52 + SELECT (command) ........................................... 31 + SENTBEFORE <date> (search key) ............................. 52 + SENTON <date> (search key) ................................. 52 + SENTSINCE <date> (search key) .............................. 52 + SHOULD (specification requirement term) .................... 4 + SHOULD NOT (specification requirement term) ................ 4 + + + +Crispin Standards Track [Page 105] + +RFC 3501 IMAPv4 March 2003 + + + SINCE <date> (search key) .................................. 52 + SMALLER <n> (search key) ................................... 52 + STARTTLS (command) ......................................... 27 + STATUS (command) ........................................... 44 + STATUS (response) .......................................... 70 + STORE (command) ............................................ 58 + SUBJECT <string> (search key) .............................. 53 + SUBSCRIBE (command) ........................................ 38 + Session Flag (class of flag) ............................... 12 + System Flag (type of flag) ................................. 11 + TEXT (part specifier) ...................................... 56 + TEXT <string> (search key) ................................. 53 + TO <string> (search key) ................................... 53 + TRYCREATE (response code) .................................. 65 + UID (command) .............................................. 60 + UID (fetch item) ........................................... 58 + UID (fetch result) ......................................... 79 + UID <sequence set> (search key) ............................ 53 + UIDNEXT (response code) .................................... 65 + UIDNEXT (status item) ...................................... 45 + UIDVALIDITY (response code) ................................ 65 + UIDVALIDITY (status item) .................................. 45 + UNANSWERED (search key) .................................... 53 + UNDELETED (search key) ..................................... 53 + UNDRAFT (search key) ....................................... 53 + UNFLAGGED (search key) ..................................... 53 + UNKEYWORD <flag> (search key) .............................. 53 + UNSEEN (response code) ..................................... 65 + UNSEEN (search key) ........................................ 53 + UNSEEN (status item) ....................................... 45 + UNSUBSCRIBE (command) ...................................... 39 + Unique Identifier (UID) (message attribute) ................ 8 + X<atom> (command) .......................................... 62 + [RFC-2822] Size (message attribute) ........................ 12 + \Answered (system flag) .................................... 11 + \Deleted (system flag) ..................................... 11 + \Draft (system flag) ....................................... 11 + \Flagged (system flag) ..................................... 11 + \Marked (mailbox name attribute) ........................... 69 + \Noinferiors (mailbox name attribute) ...................... 69 + \Noselect (mailbox name attribute) ......................... 69 + \Recent (system flag) ...................................... 11 + \Seen (system flag) ........................................ 11 + \Unmarked (mailbox name attribute) ......................... 69 + + + + + + + +Crispin Standards Track [Page 106] + +RFC 3501 IMAPv4 March 2003 + + +Author's Address + + Mark R. Crispin + Networks and Distributed Computing + University of Washington + 4545 15th Avenue NE + Seattle, WA 98105-4527 + + Phone: (206) 543-5762 + + EMail: MRC@CAC.Washington.EDU + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Crispin Standards Track [Page 107] + +RFC 3501 IMAPv4 March 2003 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2003). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. v This + document and the information contained herein is provided on an "AS + IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK + FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT + LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL + NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY + OR FITNESS FOR A PARTICULAR PURPOSE. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + + + + + + + + + + + + + + +Crispin Standards Track [Page 108] + + diff --git a/imap/docs/rfc/rfc3502.txt b/imap/docs/rfc/rfc3502.txt new file mode 100644 index 00000000..f6b61a44 --- /dev/null +++ b/imap/docs/rfc/rfc3502.txt @@ -0,0 +1,395 @@ + + + + + + +Network Working Group M. Crispin +Request for Comments: 3502 University of Washington +Category: Standards Track March 2003 + + + Internet Message Access Protocol (IMAP) - MULTIAPPEND Extension + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2003). All Rights Reserved. + +Abstract + + This document describes the multiappending extension to the Internet + Message Access Protocol (IMAP) (RFC 3501). This extension provides + substantial performance improvements for IMAP clients which upload + multiple messages at a time to a mailbox on the server. + + A server which supports this extension indicates this with a + capability name of "MULTIAPPEND". + +Terminology + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "MAY", and "OPTIONAL" in this document are to + be interpreted as described in [KEYWORDS]. + +Introduction + + The MULTIAPPEND extension permits uploading of multiple messages with + a single command. When used in conjunction with the [LITERAL+] + extension, the entire upload is accomplished in a single + command/response round trip. + + A MULTIAPPEND APPEND operation is atomic; either all messages are + successfully appended, or no messages are appended. + + In the base IMAP specification, each message must be appended in a + separate command, and there is no mechanism to "unappend" messages if + an error occurs while appending. Also, some mail stores may require + + + +Crispin Standards Track [Page 1] + +RFC 3502 IMAP MULTIAPPEND March 2003 + + + an expensive "open/lock + sync/unlock/close" operation as part of + appending; this can be quite expensive if it must be done on a + per-message basis. + + If the server supports both LITERAL+ and pipelining but not + MULTIAPPEND, it may be possible to get some of the performance + advantages of MULTIAPPEND by doing a pipelined "batch" append. + However, it will not work as well as MULTIAPPEND for the following + reasons: + + 1) Multiple APPEND commands, even as part of a pipelined batch, + are non-atomic by definition. There is no way to revert the + mailbox to the state before the batch append in the event of an + error. + + 2) It may not be feasible for the server to coalesce pipelined + APPEND operations so as to avoid the "open/lock + + sync/unlock/close" overhead described above. In any case, such + coalescing would be timing dependent and thus potentially + unreliable. In particular, with traditional UNIX mailbox files, + it is assumed that a lock is held only for a single atomic + operation, and many applications disregard any lock that is + older than 5 minutes. + + 3) If an error occurs, depending upon the nature of the error, + it is possible for additional messages to be appended after the + error. For example, the user wants to append 5 messages, but a + disk quota error occurs with the third message because of its + size. However, the fourth and fifth messages have already been + sent in the pipeline, so the mailbox ends up with the first, + second, fourth, and fifth messages of the batch appended. + +6.3.11. APPEND Command + + Arguments: mailbox name + one or more messages to upload, specified as: + OPTIONAL flag parenthesized list + OPTIONAL date/time string + message literal + + Data: no specific responses for this command + + Result: OK - append completed + NO - append error: can't append to that mailbox, error + in flags or date/time or message text, + append cancelled + BAD - command unknown or arguments invalid + + + + +Crispin Standards Track [Page 2] + +RFC 3502 IMAP MULTIAPPEND March 2003 + + + The APPEND command appends the literal arguments as new messages + to the end of the specified destination mailbox. This argument + SHOULD be in the format of an [RFC-2822] message. 8-bit + characters are permitted in the message. A server implementation + that is unable to preserve 8-bit data properly MUST be able to + reversibly convert 8-bit APPEND data to 7-bit using a [MIME-IMB] + content transfer encoding. + + Note: There MAY be exceptions, e.g., draft messages, in + which required [RFC-2822] header lines are omitted in the + message literal argument to APPEND. The full implications + of doing so MUST be understood and carefully weighed. + + If a flag parenthesized list is specified, the flags SHOULD be set + in the resulting message; otherwise, the flag list of the + resulting message is set empty by default. + + If a date-time is specified, the internal date SHOULD be set in + the resulting message; otherwise, the internal date of the + resulting message is set to the current date and time by default. + + A zero-length message literal argument is an error, and MUST + return a NO. This can be used to cancel the append. + + If the append is unsuccessful for any reason (including being + cancelled), the mailbox MUST be restored to its state before the + APPEND attempt; no partial appending is permitted. The server MAY + return an error before processing all the message arguments. + + If the destination mailbox does not exist, a server MUST return an + error, and MUST NOT automatically create the mailbox. Unless it + is certain that the destination mailbox can not be created, the + server MUST send the response code "[TRYCREATE]" as the prefix of + the text of the tagged NO response. This gives a hint to the + client that it can attempt a CREATE command and retry the APPEND + if the CREATE is successful. + + If the mailbox is currently selected, the normal new message + actions SHOULD occur. Specifically, the server SHOULD notify the + client immediately via an untagged EXISTS response. If the server + does not do so, the client MAY issue a NOOP command (or failing + that, a CHECK command) after one or more APPEND commands. + + + + + + + + + +Crispin Standards Track [Page 3] + +RFC 3502 IMAP MULTIAPPEND March 2003 + + + Example: C: A003 APPEND saved-messages (\Seen) {329} + S: + Ready for literal data + C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST) + C: From: Fred Foobar <foobar@Blurdybloop.example.COM> + C: Subject: afternoon meeting + C: To: mooch@owatagu.example.net + C: Message-Id: <B27397-0100000@Blurdybloop.example.COM> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: Hello Joe, do you think we can meet at 3:30 tomorrow? + C: (\Seen) " 7-Feb-1994 22:43:04 -0800" {295} + S: + Ready for literal data + C: Date: Mon, 7 Feb 1994 22:43:04 -0800 (PST) + C: From: Joe Mooch <mooch@OWaTaGu.example.net> + C: Subject: Re: afternoon meeting + C: To: foobar@blurdybloop.example.com + C: Message-Id: <a0434793874930@OWaTaGu.example.net> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: 3:30 is fine with me. + C: + S: A003 OK APPEND completed + C: A004 APPEND bogusname (\Flagged) {1023} + S: A004 NO [TRYCREATE] No such mailbox as bogusname + C: A005 APPEND test (\Flagged) {99} + S: + Ready for literal data + C: Date: Mon, 7 Feb 2000 22:43:04 -0800 (PST) + C: From: Fred Foobar <fred@example.com> + C: Subject: hmm... + C: {35403} + S: A005 NO APPEND failed: Disk quota exceeded + + Note: The APPEND command is not used for message delivery, + because it does not provide a mechanism to transfer [SMTP] + envelope information. + +Modification to IMAP4rev1 Base Protocol Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [ABNF]. + + append = "APPEND" SP mailbox 1*append-message + + append-message = [SP flag-list] [SP date-time] SP literal + + + + + +Crispin Standards Track [Page 4] + +RFC 3502 IMAP MULTIAPPEND March 2003 + + +MULTIAPPEND Interaction with UIDPLUS Extension + + Servers which support both MULTIAPPEND and [UIDPLUS] will have the + "resp-code-apnd" rule modified as follows: + + resp-code-apnd = "APPENDUID" SP nz-number SP set + + That is, the APPENDUID response code returns as many UIDs as there + were messages appended in the multiple append. The UIDs returned + should be in the order the articles where appended. The message set + may not contain extraneous UIDs or the symbol "*". + +Security Considerations + + The MULTIAPPEND extension does not raise any security considerations + that are not present in the base [IMAP] protocol, and these issues + are discussed in [IMAP]. Nevertheless, it is important to remember + that IMAP4rev1 protocol transactions, including electronic mail data, + are sent in the clear over the network unless protection from + snooping is negotiated, either by the use of STARTTLS, privacy + protection is negotiated in the AUTHENTICATE command, or some other + protection mechanism is in effect. + +Normative References + + [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 2234, November 1997. + + [IMAP] Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 3501, March 2003. + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [MIME-IMB] Freed, N. and N. Borenstein, "MIME (Multipurpose Internet + Mail Extensions) Part One: Format of Internet Message + Bodies", RFC 2045, November 1996. + + [RFC-2822] Resnick, P., "Internet Message Format", RFC 2822, April + 2001. + + + + + + + + + + + +Crispin Standards Track [Page 5] + +RFC 3502 IMAP MULTIAPPEND March 2003 + + +Informative References + + [LITERAL+] Myers, J., "IMAP4 non-synchronizing literals", RFC 2088, + January 1997. + + [UIDPLUS] Myers, J., "IMAP4 UIDPLUS extension", RFC 2359, June 1988. + + [SMTP] Klensin, J., Editor, "Simple Mail Transfer Protocol", RFC + 2821, April 2001. + +Author's Address + + Mark R. Crispin + Networks and Distributed Computing + University of Washington + 4545 15th Avenue NE + Seattle, WA 98105-4527 + + Phone: (206) 543-5762 + EMail: MRC@CAC.Washington.EDU + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Crispin Standards Track [Page 6] + +RFC 3502 IMAP MULTIAPPEND March 2003 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2003). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. + + This document and the information contained herein is provided on an + "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING + TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING + BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION + HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF + MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + + + + + + + + + + + + + +Crispin Standards Track [Page 7] + diff --git a/imap/docs/rfc/rfc3503.txt b/imap/docs/rfc/rfc3503.txt new file mode 100644 index 00000000..5b82fb08 --- /dev/null +++ b/imap/docs/rfc/rfc3503.txt @@ -0,0 +1,507 @@ + + + + + + +Network Working Group A. Melnikov +Request for Comments: 3503 ACI Worldwide/MessagingDirect +Category: Standards Track March 2003 + + + Message Disposition Notification (MDN) profile for + Internet Message Access Protocol (IMAP) + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2003). All Rights Reserved. + +Abstract + + The Message Disposition Notification (MDN) facility defined in RFC + 2298 provides a means by which a message can request that message + processing by the recipient be acknowledged as well as a format to be + used for such acknowledgements. However, it doesn't describe how + multiple Mail User Agents (MUAs) should handle the generation of MDNs + in an Internet Message Access Protocol (IMAP4) environment. + + This document describes how to handle MDNs in such an environment and + provides guidelines for implementers of IMAP4 that want to add MDN + support to their products. + + + + + + + + + + + + + + + + + + + +Melnikov Standards Track [Page 1] + +RFC 3503 MDN profile for IMAP March 2003 + + +Table of Contents + + 1. Conventions Used in this Document............................. 2 + 2. Introduction and Overview..................................... 2 + 3. Client behavior............................................... 3 + 3.1. Client behavior when receiving a message................. 5 + 3.2. Client behavior when copying a message................... 5 + 3.3. Client behavior when sending a message................... 5 + 3.4. Client behavior when saving a temporary message.......... 5 + 4. Server behavior............................................... 5 + 4.1. Server that supports arbitrary keywords.................. 5 + 4.2. Server that supports only $MDNSent keyword............... 5 + 4.3. Interaction with IMAP ACL extension...................... 6 + 5. Examples...................................................... 6 + 6. Security Considerations....................................... 7 + 7. Formal Syntax................................................. 7 + 8. Acknowledgments............................................... 7 + 9. Normative References.......................................... 8 + 10. Author's Address.............................................. 8 + 11. Full Copyright Statement...................................... 9 + +1. Conventions Used in this Document + + "C:" and "S:" in examples show lines sent by the client and server + respectively. + + The keywords "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in + this document when typed in uppercase are to be interpreted as + defined in "Key words for use in RFCs to Indicate Requirement Levels" + [KEYWORDS]. + +2. Introduction and Overview + + This memo defines an additional [IMAP4] mailbox keyword that allows + multiple Mail User Agents (MUAs) to know if a requested receipt + notification was sent. + + Message Disposition Notification [MDN] does not require any special + support of IMAP in the case where a user has access to the mailstore + from only one computer and is using a single MUA. In this case, the + MUA behaves as described in [MDN], i.e., the MUA performs automatic + processing and generates corresponding MDNs, it performs requested + action and, with the user's permission, sends appropriate MDNs. The + MUA will not send MDN twice because the MUA keeps track of sent + notifications in a local configuration. However, that does not work + when IMAP is used to access the same mailstore from different + locations or is using different MUAs. + + + + +Melnikov Standards Track [Page 2] + +RFC 3503 MDN profile for IMAP March 2003 + + + This document defines a new special purpose mailbox keyword $MDNSent + that must be used by MUAs. It does not define any new command or + response for IMAP, but describes a technique that MUAs should use to + achieve interoperability. + + When a client opens a mailbox for the first time, it verifies that + the server is capable of storing the $MDNSent keyword by examining + the PERMANENTFLAGS response code. In order to support MDN in IMAP, a + server MUST support either the $MDNSent keyword, or arbitrary message + keywords. + +3. Client behavior + + The use of IMAP requires few additional steps in mail processing on + the client side. The following timeline modifies the timeline found + in Section 4 of [MDN]. + + -- User composes message. + + -- User tells MUA to send message. + + -- MUA passes message to MSA (original recipient information passed + along). MUA [optionally] saves message to a folder for sent mail + with $MDNSent flag set. + + -- MSA sends message to MTA. + + -- Final MTA receives message. + + -- Final MTA delivers message to MUA (possibly generating DSN). + + -- MUA logs into IMAP server, opens mailbox, verifies if mailbox can + store $MDNSent keyword by examining PERMANENTFLAGS response. + + -- MUA performs automatic processing and generates corresponding MDNs + ("dispatched", "processed", "deleted", "denied" or "failed" + disposition type with "automatic-action" and "MDN-sent- + automatically" disposition modes) for messages that do not have + $MDNSent keyword, or \Draft flag set. (*) + + -- MUA sets the $MDNSent keyword for every message that required an + automatic MDN to be sent, whether or not the MDN was sent. + + -- MUA displays a list of messages to user. + + -- User selects a message and requests that some action be performed + on it. + + + + +Melnikov Standards Track [Page 3] + +RFC 3503 MDN profile for IMAP March 2003 + + + -- MUA performs requested action and, with user's permission, sends + appropriate MDN ("displayed", "dispatched", "processed", + "deleted", "denied" or "failed" disposition type with "manual- + action" and "MDN-sent-manually" or "MDN-sent-automatically" + disposition mode). If the generated MDN is saved to a mailbox + with the APPEND command, the client MUST specify the $MDNSent + keyword in the APPEND. + + -- MUA sets the $MDNSent keyword for all messages for which the user + confirmed the dispatching of disposition (or was explicitly + prohibited to do so). + + -- User possibly performs other actions on message, but no further + MDNs are generated. + + (*) Note: MUA MUST NOT use \Recent flag as an indicator that it + should send MDN, because according to [IMAP4], "If multiple + connections have the same mailbox selected simultaneously, it is + undefined which of these connections will see newly-arrived + messages with \Recent set and which will see it without \Recent + set". Thus, using \Recent as an indicator will cause + unpredictable client behavior with different IMAP4 servers. + However, the client MAY use \Seen flag as one of the indicators + that MDN must not be sent. The client MUST NOT use any other + standard flags, like \Draft or \Answered, to indicate that MDN + was previously sent, because they have different well known + meaning. In any case, in the presence of the $MDNSent keyword, + the client MUST ignore all other flags or keywords for the + purpose of generating an MDN and MUST NOT send the MDN. + + When the client opens a mailbox for the first time, it must verify + that the server supports the $MDNSent keyword, or arbitrary message + keywords by examining PERMANENTFLAGS response code. + + The client MUST NOT try to set the $MDNSent keyword if the server is + incapable of storing it permanently. + + The client MUST be prepared to receive NO from the server as the + result of STORE $MDNSent when the server advertises the support of + storing arbitrary keywords, because the server may limit the number + of message keywords it can store in a particular mailbox. A client + SHOULD NOT send MDN if it fails to store the $MDNSent keyword. + + Once the $MDNSent keyword is set, it MUST NOT be unset by a client. + The client MAY set the $MDNSent keyword when a user denies sending + the notification. This prohibits all other MUAs from sending MDN for + this message. + + + + +Melnikov Standards Track [Page 4] + +RFC 3503 MDN profile for IMAP March 2003 + + +3.1. Client behavior when receiving a message + + The client MUST NOT send MDN if a message has the $MDNSent keyword + set. It also MUST NOT send MDN if a message has \Draft flag, because + some clients use this flag to mark a message as incomplete. + + See the timeline in section 3 for details on client behavior when + receiving a message. + +3.2. Client behavior when copying a message + + The client SHOULD verify that $MDNSent is preserved on a COPY + operation. Furthermore, when a message is copied between servers + with the APPEND command, the client MUST set the $MDNSent keyword + correctly. + +3.3. Client behavior when sending a message + + When saving a sent message to any folder, the client MUST set the + $MDNSent keyword to prevent another client from sending MDN for the + message. + +3.4. Client behavior when saving a temporary message + + When saving an unfinished message to any folder client MUST set + $MDNSent keyword to prevent another client from sending MDN for the + message. + +4. Server behavior + + Server implementors that want to follow this specification must + insure that their server complies with either section 4.1 or section + 4.2. If the server also supports the IMAP [ACL] extension, it MUST + also comply with the section 4.3. + +4.1. Server that supports arbitrary keywords + + No changes are required from the server to make it compatible with + the extension described in this document if it supports arbitrary + keywords. + +4.2. Server that supports only $MDNSent keyword + + Servers that support only the $MDNSent keyword MUST preserve it on + the COPY operation. It is also expected that a server that supports + SEARCH <flag> will also support the SEARCH KEYWORD $MDNSent. + + + + + +Melnikov Standards Track [Page 5] + +RFC 3503 MDN profile for IMAP March 2003 + + +4.3. Interaction with IMAP ACL extension + + Any server that conforms to either 4.1 or 4.2 and also supports the + IMAP [ACL] extension, SHOULD preserve the $MDNSent keyword on COPY + even if the client does not have 'w' right. This will prevent the + generation of a duplicated MDN for the same message. Note that the + server MUST still check if the client has rights to perform the COPY + operation on a message according to [ACL]. + +5. Examples + + 1) MUA opens mailbox for the first time. + + a) The server supports storing of arbitrary keywords + + C: a100 select INBOX + S: * FLAGS (\Flagged \Draft \Deleted \Seen) + S: * OK [PERMANENTFLAGS (\Flagged \Draft \Deleted \Seen \*)] + S: * 5 EXISTS + S: * 3 RECENT + S: * OK [UIDVALIDITY 894294713] + S: a100 OK [READ-WRITE] Completed + + b) The server supports storing of the $MDNSent keyword + + C: a100 select INBOX + S: * FLAGS (\Flagged \Draft \Deleted \Seen $MDNSent) + S: * OK [PERMANENTFLAGS (\Flagged \Draft \Deleted \Seen $MDNSent)] + S: * 5 EXISTS + S: * 3 RECENT + S: * OK [UIDVALIDITY 894294713] + S: a100 OK [READ-WRITE] Completed + + 2) The MUA successfully sets the $MDNSent keyword + + C: a200 STORE 4 +FLAGS ($MDNSent) + S: * 4 FETCH (FLAGS (\Flagged \Seen $MDNSent)) + S: * FLAGS ($MDNSent \Flagged \Deleted \Draft \Seen) + S: * OK [PERMANENTFLAGS ($MDNSent \Flagged \Deleted \Draft \Seen \*)] + S: a200 OK STORE completed + + 3) The server refuses to store the $MDNSent keyword + + C: a200 STORE 4 +FLAGS ($MDNSent) + S: a200 NO STORE failed : no space left to store $MDNSent keyword + + + + + + +Melnikov Standards Track [Page 6] + +RFC 3503 MDN profile for IMAP March 2003 + + + 4) All clients and servers MUST treat the $MDNSent keyword as case + insensitive in all operations, as stated in [IMAP]. + + C: a300 FETCH 1:* FLAGS + S: * 1 FETCH (FLAGS (\Seen)) + S: * 2 FETCH (FLAGS (\Answered \Seen $MdnSENt)) + S: * 3 FETCH (FLAGS ()) + S: * 4 FETCH (FLAGS (\Flagged \Seen $MdnSENT)) + S: * 5 FETCH (FLAGS ($MDNSent)) + S: * 6 FETCH (FLAGS (\Recent)) + S: a300 OK FETCH completed + C: a400 SEARCH KEYWORDS $mdnsent + S: * SEARCH 2 4 5 + S: a400 OK SEARCH completed + +6. Security Considerations + + There are no known security issues with this extension, not found in + [MDN] and/or [IMAP4]. + + Section 4.3 changes ACL checking requirements on an IMAP server that + implements IMAP [ACL] extension. + +7. Formal Syntax + + The following syntax specification uses the augmented Backus-Naur + Form (BNF) notation as specified in [RFC-822], as modified by + [IMAP4]. Non-terminals referenced, but not defined below, are as + defined by [IMAP4]. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper or lower case characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + flag_keyword ::= "$MDNSent" / other_keywords + + other_keywords ::= atom + +8. Acknowledgments + + This document is the product of discussions that took place on the + IMAP mailing list. Special gratitude to Cyrus Daboo and Randall + Gellens for reviewing the document. + + Thank you to my father who as he has helped to make me what I am. I + miss you terribly. + + + + +Melnikov Standards Track [Page 7] + +RFC 3503 MDN profile for IMAP March 2003 + + +9. Normative References + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [MDN] Fajman, R., "An Extensible Message Format for Message + Disposition Notifications", RFC 2298, March 1998. + + [IMAP4] Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 3501, March 2003. + + [ACL] Myers, J., "IMAP4 ACL extension", RFC 2086, January 1997. + +10. Author's Address + + Alexey Melnikov + ACI Worldwide/MessagingDirect + 59 Clarendon Road + Watford, Hertfordshire + United Kingdom, WD17 1FQ + + Phone: +44 1923 81 2877 + EMail: mel@messagingdirect.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov Standards Track [Page 8] + +RFC 3503 MDN profile for IMAP March 2003 + + +11. Full Copyright Statement + + Copyright (C) The Internet Society (2003). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. + + This document and the information contained herein is provided on an + "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING + TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING + BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION + HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF + MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + + + + + + + + + + + + + +Melnikov Standards Track [Page 9] + diff --git a/imap/docs/rfc/rfc3516.txt b/imap/docs/rfc/rfc3516.txt new file mode 100644 index 00000000..4d021975 --- /dev/null +++ b/imap/docs/rfc/rfc3516.txt @@ -0,0 +1,451 @@ + + + + + + +Network Working Group L. Nerenberg +Request for Comments: 3516 Orthanc Systems +Category: Standards Track April 2003 + + + IMAP4 Binary Content Extension + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2003). All Rights Reserved. + +Abstract + + This memo defines the Binary extension to the Internet Message Access + Protocol (IMAP4). It provides a mechanism for IMAP4 clients and + servers to exchange message body data without using a MIME content- + transfer-encoding. + +1. Conventions Used in this Document + + The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" + in this document are to be interpreted as described in [KEYWORD]. + + The abbreviation "CTE" means content-transfer-encoding. + +2. Introduction + + The MIME extensions to Internet messaging allow for the transmission + of non-textual (binary) message content [MIME-IMB]. Since the + traditional transports for messaging are not always capable of + passing binary data transparently, MIME provides encoding schemes + that allow binary content to be transmitted over transports that are + not otherwise able to do so. + + The overhead of MIME-encoding this content can be considerable in + some contexts (e.g., slow radio links, streaming multimedia). + Reducing the overhead associated with CTE schemes such as base64 + + + + + + +Nerenberg Standards Track [Page 1] + +RFC 3516 IMAP4 Binary Content Extension April 2003 + + + can give a noticeable reduction in resource consumption. The Binary + extension lets the server perform CTE decoding prior to transmitting + message data to the client. + +3. Content-Transfer-Encoding Considerations + + Every IMAP4 body section has a MIME content-transfer-encoding. + (Those without an explicit Content-Transfer-Encoding header are + implicitly labeled as "7bit" content.) In the terminology of [MIME- + IMB], the CTE specifies both a decoding algorithm and the domain of + the decoded data. In this memo, "decoding" refers to the CTE + decoding step described in [MIME-IMB]. + + Certain CTEs use an identity encoding transformation. For these CTEs + there is no decoding required, however the domain of the underlying + data may not be expressible in the IMAP4 protocol (e.g., MIME + "binary" content containing NUL octets). To accommodate these cases + the Binary extension introduces a new type of literal protocol + element that is fully eight bit transparent. + + Thus, server processing of the FETCH BINARY command involves two + logical steps: + + 1) perform any CTE-related decoding + + 2) determine the domain of the decoded data + + Step 2 is necessary to determine which protocol element should be + used to transmit the decoded data. (See FETCH Response Extensions + for further details.) + +4. Framework for the IMAP4 Binary Extension + + This memo defines the following extensions to [IMAP4rev1]. + +4.1. CAPABILITY Identification + + IMAP4 servers that support this extension MUST include "BINARY" in + the response list to the CAPABILITY command. + +4.2. FETCH Command Extensions + + This extension defines three new FETCH command data items. + + BINARY<section-binary>[<partial>] + + Requests that the specified section be transmitted after + performing CTE-related decoding. + + + +Nerenberg Standards Track [Page 2] + +RFC 3516 IMAP4 Binary Content Extension April 2003 + + + The <partial> argument, if present, requests that a subset of + the data be returned. The semantics of a partial FETCH BINARY + command are the same as for a partial FETCH BODY command, with + the exception that the <partial> arguments refer to the DECODED + section data. + + BINARY.PEEK<section-binary>[<partial>] + + An alternate form of FETCH BINARY that does not implicitly set + the \Seen flag. + + BINARY.SIZE<section-binary> + + Requests the decoded size of the section (i.e., the size to + expect in response to the corresponding FETCH BINARY request). + + Note: client authors are cautioned that this might be an + expensive operation for some server implementations. + Needlessly issuing this request could result in degraded + performance due to servers having to calculate the value every + time the request is issued. + +4.3. FETCH Response Extensions + + This extension defines two new FETCH response data items. + + BINARY<section-binary>[<<number>>] + + An <nstring> or <literal8> expressing the content of the + specified section after removing any CTE-related encoding. If + <number> is present it refers to the offset within the DECODED + section data. + + If the domain of the decoded data is "8bit" and the data does + not contain the NUL octet, the server SHOULD return the data in + a <string> instead of a <literal8>; this allows the client to + determine if the "8bit" data contains the NUL octet without + having to explicitly scan the data stream for for NULs. + + If the server does not know how to decode the section's CTE, it + MUST fail the request and issue a "NO" response that contains + the "UNKNOWN-CTE" extended response code. + + + + + + + + + +Nerenberg Standards Track [Page 3] + +RFC 3516 IMAP4 Binary Content Extension April 2003 + + + BINARY.SIZE<section-binary> + + The size of the section after removing any CTE-related + encoding. The value returned MUST match the size of the + <nstring> or <literal8> that will be returned by the + corresponding FETCH BINARY request. + + If the server does not know how to decode the section's CTE, it + MUST fail the request and issue a "NO" response that contains + the "UNKNOWN-CTE" extended response code. + +4.4. APPEND Command Extensions + + The APPEND command is extended to allow the client to append data + containing NULs by using the <literal8> syntax. The server MAY + modify the CTE of the appended data, however any such transformation + MUST NOT result in a loss of data. + + If the destination mailbox does not support the storage of binary + content, the server MUST fail the request and issue a "NO" response + that contains the "UNKNOWN-CTE" extended response code. + +5. MIME Encoded Headers + + [MIME-MHE] defines an encoding that allows for non-US-ASCII text in + message headers. This encoding is not the same as the content- + transfer-encoding applied to message bodies, and the decoding + transformations described in this memo do not apply to [MIME-MHE] + encoded header text. A server MUST NOT perform any conversion of + [MIME-MHE] encoded header text in response to any binary FETCH or + APPEND request. + +6. Implementation Considerations + + Messaging clients and servers have been notoriously lax in their + adherence to the Internet CRLF convention for terminating lines of + textual data in Internet protocols. When sending data using the + Binary extension, servers MUST ensure that textual line-oriented + sections are always transmitted using the IMAP4 CRLF line termination + syntax, regardless of the underlying storage representation of the + data on the server. + + A server may choose to store message body binary content in a non- + encoded format. Regardless of the internal storage representation + used, the server MUST issue BODYSTRUCTURE responses that describe the + message as though the binary-encoded sections are encoded in a CTE + + + + + +Nerenberg Standards Track [Page 4] + +RFC 3516 IMAP4 Binary Content Extension April 2003 + + + acceptable to the IMAP4 base specification. Furthermore, the results + of a FETCH BODY MUST return the message body content in the format + described by the corresponding FETCH BODYSTRUCTURE response. + + While the server is allowed to modify the CTE of APPENDed <literal8> + data, this should only be done when it is absolutely necessary. + Gratuitous encoding changes will render useless most cryptographic + operations that have been performed on the message. + + This extension provides an optimization that is useful in certain + specific situations. It does not absolve clients from providing + basic functionality (content transfer decoding) that should be + available in all messaging clients. Clients supporting this + extension SHOULD be prepared to perform their own CTE decoding + operations. + +7. Formal Protocol Syntax + + The following syntax specification uses the augmented Backus-Naur + Form (ABNF) notation as used in [ABNF], and incorporates by reference + the Core Rules defined in that document. + + This syntax augments the grammar specified in [IMAP4rev1]. + + append =/ "APPEND" SP mailbox [SP flag-list] + [SP date-time] SP literal8 + + fetch-att =/ "BINARY" [".PEEK"] section-binary [partial] + / "BINARY.SIZE" section-binary + + literal8 = "~{" number "}" CRLF *OCTET + ; <number> represents the number of OCTETs + ; in the response string. + + msg-att-static =/ "BINARY" section-binary SP (nstring / literal8) + / "BINARY.SIZE" section-binary SP number + + partial = "<" number "." nz-number ">" + + resp-text-code =/ "UNKNOWN-CTE" + + section-binary = "[" [section-part] "]" + + + + + + + + + +Nerenberg Standards Track [Page 5] + +RFC 3516 IMAP4 Binary Content Extension April 2003 + + +8. Normative References + + [ABNF] Crocker, D., Editor, and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", RFC 2234, November 1997. + + [IMAP4rev1] Crispin, M., "Internet Message Access Protocol Version + 4rev1", RFC 3501, March 2003. + + [KEYWORD] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [MIME-IMB] Freed, N. and N. Borenstein, "Multipurpose Internet Mail + Extensions (MIME) Part One: Format of Internet Message + Bodies", RFC 2045, November 1996. + + [MIME-MHE] Moore, K., "MIME (Multipurpose Internet Mail Extensions) + Part Three: Message Header Extensions for Non-ASCII + Text", RFC 2047, November 1996. + +9. Security Considerations + + There are no known additional security issues with this extension + beyond those described in the base protocol described in [IMAP4rev1]. + +10. Intellectual Property + + The IETF takes no position regarding the validity or scope of any + intellectual property or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; neither does it represent that it + has made any effort to identify any such rights. Information on the + IETF's procedures with respect to rights in standards-track and + standards-related documentation can be found in BCP-11. Copies of + claims of rights made available for publication and any assurances of + licenses to be made available, or the result of an attempt made to + obtain a general license or permission for the use of such + proprietary rights by implementors or users of this specification can + be obtained from the IETF Secretariat. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights which may cover technology that may be required to practice + this standard. Please address the information to the IETF Executive + Director. + + + + + + +Nerenberg Standards Track [Page 6] + +RFC 3516 IMAP4 Binary Content Extension April 2003 + + +11. Author's Address + + Lyndon Nerenberg + Orthanc Systems + 1606 - 10770 Winterburn Road + Edmonton, Alberta + Canada T5S 1T6 + + EMail: lyndon@orthanc.ab.ca + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Nerenberg Standards Track [Page 7] + +RFC 3516 IMAP4 Binary Content Extension April 2003 + + +12. Full Copyright Statement + + Copyright (C) The Internet Society (2003). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. + + This document and the information contained herein is provided on an + "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING + TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING + BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION + HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF + MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + + + + + + + + + + + + + +Nerenberg Standards Track [Page 8] + diff --git a/imap/docs/rfc/rfc3656.txt b/imap/docs/rfc/rfc3656.txt new file mode 100644 index 00000000..6c0ab5b1 --- /dev/null +++ b/imap/docs/rfc/rfc3656.txt @@ -0,0 +1,1067 @@ + + + + + + +Network Working Group R. Siemborski +Request for Comments: 3656 Carnegie Mellon University +Category: Experimental December 2003 + + + The Mailbox Update (MUPDATE) + Distributed Mailbox Database Protocol + +Status of this Memo + + This memo defines an Experimental Protocol for the Internet + community. It does not specify an Internet standard of any kind. + Discussion and suggestions for improvement are requested. + Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2003). All Rights Reserved. + +Abstract + + As the demand for high-performance mail delivery agents increases, it + becomes apparent that single-machine solutions are inadequate to the + task, both because of capacity limits and that the failure of the + single machine means a loss of mail delivery for all users. It is + preferable to allow many machines to share the responsibility of mail + delivery. + + The Mailbox Update (MUPDATE) protocol allows a group of Internet + Message Access Protocol (IMAP) or Post Office Protocol - Version 3 + (POP3) servers to function with a unified mailbox namespace. This + document is intended to serve as a reference guide to that protocol. + + + + + + + + + + + + + + + + + + + +Siemborski Experimental [Page 1] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 + 2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3 + 2.1. Atoms . . . . . . . . . . . . . . . . . . . . . . . . . 4 + 2.2. Strings . . . . . . . . . . . . . . . . . . . . . . . . 4 + 3. Server Responses . . . . . . . . . . . . . . . . . . . . . . 4 + 3.1. Response: OK . . . . . . . . . . . . . . . . . . . . . 5 + 3.2. Response: NO . . . . . . . . . . . . . . . . . . . . . 5 + 3.3. Response: BAD . . . . . . . . . . . . . . . . . . . . . 5 + 3.4. Response: BYE . . . . . . . . . . . . . . . . . . . . . 6 + 3.5. Response: RESERVE . . . . . . . . . . . . . . . . . . . 6 + 3.6. Response: MAILBOX . . . . . . . . . . . . . . . . . . . 6 + 3.7. Response: DELETE . . . . . . . . . . . . . . . . . . . 7 + 3.8. Server Capability Response. . . . . . . . . . . . . . . 7 + 4. Client Commands . . . . . . . . . . . . . . . . . . . . . . . 8 + 4.1. Command: ACTIVATE . . . . . . . . . . . . . . . . . . . 8 + 4.2. Command: AUTHENTICATE . . . . . . . . . . . . . . . . . 8 + 4.3. Command: DEACTIVATE . . . . . . . . . . . . . . . . . . 9 + 4.4. Command: DELETE . . . . . . . . . . . . . . . . . . . . 9 + 4.5. Command: FIND . . . . . . . . . . . . . . . . . . . . . 9 + 4.6. Command: LIST . . . . . . . . . . . . . . . . . . . . . 10 + 4.7. Command: LOGOUT . . . . . . . . . . . . . . . . . . . . 10 + 4.8. Command: NOOP . . . . . . . . . . . . . . . . . . . . . 10 + 4.9. Command: RESERVE. . . . . . . . . . . . . . . . . . . . 10 + 4.10. Command: STARTTLS . . . . . . . . . . . . . . . . . . . 11 + 4.11. Command: UPDATE . . . . . . . . . . . . . . . . . . . . 12 + 5. MUPDATE Formal Syntax . . . . . . . . . . . . . . . . . . . . 12 + 6. MUPDATE URL Scheme. . . . . . . . . . . . . . . . . . . . . . 14 + 6.1. MUPDATE URL Scheme Registration Form. . . . . . . . . . 14 + 7. Security Considerations . . . . . . . . . . . . . . . . . . . 15 + 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 + 9. Intellectual Property Rights. . . . . . . . . . . . . . . . . 16 + 10. References. . . . . . . . . . . . . . . . . . . . . . . . . . 17 + 10.1. Normative References. . . . . . . . . . . . . . . . . . 17 + 10.2. Informative References. . . . . . . . . . . . . . . . . 17 + 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 + 12. Author's Address. . . . . . . . . . . . . . . . . . . . . . . 18 + 13. Full Copyright Statement. . . . . . . . . . . . . . . . . . . 19 + + + + + + + + + + + + +Siemborski Experimental [Page 2] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + +1. Introduction + + In order to support an architecture where there are multiple [IMAP, + POP3] servers sharing a common mailbox database, it is necessary to + be able to provide atomic mailbox operations, as well as offer + sufficient guarantees about database consistency. + + The primary goal of the MUPDATE protocol is to be simple to implement + yet allow for database consistency between participants. + + The key words "MUST, "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", + "RECOMMENDED", and "MAY" in this document are to be interpreted as + defined in BCP 14, RFC 2119 [KEYWORDS]. + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. + +2. Protocol Overview + + The MUPDATE protocol assumes a reliable data stream such as a TCP + network connection. IANA has registered port 3905 with a short name + of "mupdate" for this purpose. + + In the current implementation of the MUPDATE protocol there are three + types of participants: a single master server, slave (or replica) + servers, and clients. The master server maintains an authoritative + copy of the mailbox database. Slave servers connect to the MUPDATE + master server as clients, and function as replicas from the point of + view of end clients. End clients may connect to either the master or + any slave and perform searches against the database, however + operations that change the database can only be performed against the + master. For the purposes of protocol discussion we will consider a + slave's connection to the master identical to that of any other + client. + + After connection, all commands from a client to server must have an + associated unique tag which is an alphanumeric string. Commands MAY + be pipelined from the client to the server (that is, the client need + not wait for the response before sending the next command). The + server MUST execute the commands in the order they were received, + however. + + If the server supports an inactivity login timeout, it MUST be at + least 15 minutes. + + + + + + + +Siemborski Experimental [Page 3] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + + MUPDATE uses data formats similar to those used in [ACAP]. That is, + atoms and strings. All commands and tags in the protocol are + transmitted as atoms. All other data is considered to a string, and + must be quoted or transmitted as a literal. + + Outside of a literal, both clients and servers MUST support line + lengths of at least 1024 octets (including the trailing CR and LF + characters). If a line of a longer length must be transmitted, + implementations MUST make use of literals to do so. + +2.1. Atoms + + An atom consists of one or more alphanumeric characters. Atoms MUST + be less than 15 octets in length. + +2.2. Strings + + As in [ACAP], a string may be either literal or a quoted string. A + literal is a sequence of zero or more octets (including CR and LF), + prefix-quoted with an octet count in the form of an open brace ("{"), + the number of octets, an optional plus sign to indicate that the data + follows immediately (a non-synchronized literal), a close brace + ("}"), and a CRLF sequence. If the plus sign is omitted (a + synchronized literal), then the receiving side MUST send a "+ go + ahead" response, and the sending side MUST wait for this response. + Servers MUST support literals of atleast 4096 octets. + + Strings that are sent from server to client SHOULD NOT be in the + synchronized literal format. + + A quoted string is a sequence of zero or more 7-bit characters, + excluding CR, LF, and the double quote (<">), with double quote + characters at each end. + + The empty string is represented as either "" (a quoted string with + zero characters between double quotes) or as {0} followed by CRLF (a + literal with an octet count of 0). + +3. Server Responses + + Every client command in the MUPDATE protocol may receive one or more + tagged responses from the server. Each response is preceded by the + same tag as the command that elicited the response from the server. + + + + + + + + +Siemborski Experimental [Page 4] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + +3.1. Response: OK + + A tagged OK response indicates that the operation completed + successfully. There is a mandatory implementation-defined string + after the OK response. This response also indicates the beginning of + the streaming update mode when given in response to an UPDATE + command. + + Example: + +C: N01 NOOP +S: N01 OK "NOOP Complete" + +3.2. Response: NO + + A tagged NO response indicates that the operation was explicitly + denied by the server or otherwise failed. There is a mandatory + implementation-defined string after the NO response that SHOULD + explain the reason for denial. + + Example: + +C: A01 AUTHENTICATE "PLAIN" +S: A01 NO "PLAIN is not a supported SASL mechanism" + +3.3. Response: BAD + + A tagged BAD response indicates that the command from the client + could not be parsed or understood. There is a mandatory + implementation-defined string after the BAD response to provide + additional information about the error. Note that untagged BAD + responses are allowed if it is unclear what the tag for a given + command is (for example, if a blank line is received by the mupdate + server, it can generate an untagged BAD response). In the case of an + untagged response, the tag should be replaced with a "*". + + Example: + +C: C01 SELECT "INBOX" +S: C01 BAD "This is not an IMAP server" +C: +S: * BAD "Need Command" + + + + + + + + + +Siemborski Experimental [Page 5] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + +3.4. Response: BYE + + A tagged BYE response indicates that the server has decided to close + the connection. There is a mandatory implementation-defined string + after the BYE response that SHOULD explain the reason for closing the + connection. The server MUST close the connection immediately after + transmitting the BYE response. + + Example: + +C: L01 LOGOUT +S: L01 BYE "User Logged Out" + +3.5. Response: RESERVE + + A tagged RESERVE response may only be given in response to a FIND, + LIST, or UPDATE command. It includes two parameters: the name of the + mailbox that is being reserved (in mUTF-7 encoding, as specified in + [IMAP]) and a location string whose contents is defined by the + clients that are using the database, though it is RECOMMENDED that + the format of this string be the hostname of the server which is + storing the mailbox. + + This response indicates that the given name is no longer available in + the namespace, though it does not indicate that the given mailbox is + available to clients at the current time. + + Example: + +S: U01 RESERVE "internet.bugtraq" "mail2.example.org" + +3.6. Response: MAILBOX + + A tagged MAILBOX response may only be given in response to a FIND, + LIST, or UPDATE command. It includes three parameters: the name of + the mailbox, a location string (as with RESERVE), and a client- + defined string that specifies the IMAP ACL [IMAP-ACL] of the mailbox. + This message indicates that the given mailbox is ready to be accessed + by clients. + + Example: + +S: U01 MAILBOX "internet.bugtraq" "mail2.example.org" "anyone rls" + + + + + + + + +Siemborski Experimental [Page 6] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + +3.7. Response: DELETE + + A tagged DELETE response may only be given in response to an UPDATE + command, and MUST NOT be given before the OK response to the UPDATE + command is given. It contains a single parameter, that of the + mailbox that should be deleted from the slave's database. This + response indicates that the given mailbox no longer exists in the + namespace of the database, and may be given for any mailbox name, + active, reserved, or nonexistent. (Though implementations SHOULD NOT + issue DELETE responses for nonexistent mailboxes). + + Example: + +S: U01 DELETE "user.rjs3.sent-mail-jan-2002" + +3.8. Server Capability Response + + Upon connection of the client to the server, and directly following a + successful STARTTLS command, the server MUST issue a capabilities + banner, of the following format: + + The banner MUST contain a line that begins with "* AUTH" and contain + a space-separated list of SASL mechanisms that the server will accept + for authentication. The mechanism names are transmitted as atoms. + Servers MAY advertise no available mechanisms (to indicate that + STARTTLS must be completed before authentication may occur). If + STARTTLS is not supported by the server, then the line MUST contain + at least one mechanism. + + If the banner is being issued without a TLS layer, and the server + supports the STARTTLS command, the banner MUST contain the line "* + STARTTLS". If the banner is being issued under a TLS layer (or the + server does not support STARTTLS), the banner MUST NOT contain this + line. + + The last line of the banner MUST start with "* OK MUPDATE" and be + followed by four strings: the server's hostname, an implementation- + defined string giving the name of the implementation, an + implementation-defined string giving the version of the + implementation, and a string that indicates if the server is a master + or a slave. The master/slave indication MUST be either "(master)" or + an MUPDATE URL that defines where the master can be contacted. + + Any unrecognized responses before the "* OK MUPDATE" response MUST be + ignored by the client. + + + + + + +Siemborski Experimental [Page 7] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + + Example: + +S: * AUTH KERBEROS_V4 GSSAPI +S: * STARTTLS +S: * OK MUPDATE "mupdate.example.org" "Cyrus" "v2.1.2" "(master)" + +4. Client Commands + + The following are valid commands that a client may send to the + MUPDATE server: AUTHENTICATE, ACTIVATE, DEACTIVATE, DELETE, FIND, + LIST, LOGOUT, NOOP, RESERVE, STARTTLS, and UPDATE. + + Before a successful AUTHENTICATE command has occurred, the server + MUST NOT accept any commands except for AUTHENTICATE, STARTTLS, and + LOGOUT (and SHOULD reply with a NO response for all other commands). + +4.1. Command: ACTIVATE + + The ACTIVATE command has 3 parameters: the mailbox name, its + location, and its ACL. This command MUST NOT not be issued to a + slave server. + + This command can also be used to update the ACL or location + information of a mailbox. Note that it is not a requirement for a + mailbox to be reserved (or even exist in the database) for an + ACTIVATE command to succeed, implementations MUST allow this behavior + as it facilitates synchronization of the database with the current + state of the mailboxes. + +4.2. Command: AUTHENTICATE + + The AUTHENTICATE command initiates a [SASL] negotiation session + between the client and the server. It has two parameters. The first + parameter is mandatory, and is a string indicating the desired [SASL] + mechanism. The second is a string containing an optional BASE64 + encoded (as defined in section 6.8 of [MIME]) client first send. + + All of the remaining SASL blobs that are sent MUST be sent across the + wire must be in BASE64 encoded format, and followed by a CR and LF + combination. They MUST NOT be encoded as strings. + + Clients may cancel authentication by sending a * followed by a CR and + LF. + + The [SASL] service name for the MUPDATE protocol is "mupdate". + Implementations are REQUIRED to implement the GSSAPI [SASL] + mechanism, though they SHOULD implement as many mechanisms as + possible. + + + +Siemborski Experimental [Page 8] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + + If a security layer is negotiated, it should be used directly + following the CR and LF combination at the end of the server's OK + response (i.e., beginning with the client's next command) Only one + successful AUTHENTICATE command may be issued per session. + +4.3. Command: DEACTIVATE + + The DEACTIVATE command takes two parameters, the mailbox name and + location data. The mailbox MUST already exist and be activated on + the MUPDATE server. If the server responds OK, then the mailbox name + has been moved to the RESERVE state. If the server responds NO, then + the mailbox name has not been moved (for example, the mailbox was not + already active). Any ACL information that is known about the mailbox + MAY be lost when a DEACTIVATE succeeds. This command MUST NOT be + issued to a slave. + + Example: + +C: A01 DEACTIVATE "user.rjs3.new" "mail3.example.org!u4" +S: A01 OK "Mailbox Reserved." + +4.4. Command: DELETE + + The DELETE command takes only a single parameter, the mailbox name to + be removed from the database's namespace. The server SHOULD give a + NO response if the mailbox does not exist. This command MUST NOT be + issued to a slave server. + +4.5. Command: FIND + + The FIND command takes a single parameter, a mailbox name. The + server then responds with the current record for the given mailbox, + if any, and an OK response. + + Example (mailbox does not exist): + +C: F01 FIND "user.rjs3.xyzzy" +S: F01 OK "Search Complete" + + Example (mailbox is reserved): + +C: F01 FIND "user.rjs3" +S: F01 RESERVE "user.rjs3" "mail4.example.org" +S: F01 OK "Search Complete" + + + + + + + +Siemborski Experimental [Page 9] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + +4.6. Command: LIST + + The LIST command is similar to running FIND across the entire + database. The LIST command takes a single optional parameter, which + is a prefix to try to match against the location field of the + records. Without the parameter, LIST returns every record in the + database. + + For each mailbox that matches, either a MAILBOX or a RESERVE response + (as applicable) is sent to the client. When all responses are + complete, an OK response is issued. + + Example: + +C: L01 LIST +S: L01 RESERVE "user.rjs3" "mail4.example.org!u2" +S: L01 MAILBOX "user.leg" "mail2.example.org!u1" "leg lrswipcda" +S: L01 OK "List Complete" +C: L02 LIST "mail4.example.org!" +S: L02 RESERVE "user.rjs3" "mail4.example.org!u2" +S: L02 OK "List Complete" + +4.7. Command: LOGOUT + + The LOGOUT command tells the server to close the connection. Its + only valid response is the BYE response. The LOGOUT command takes no + parameters. + +4.8. Command: NOOP + + The NOOP command takes no parameters. Provided the client is + authenticated, its only acceptable response is an OK. Any idle + timeouts that the server may have on the connection SHOULD be reset + upon receipt of this command. + + If this command is issued after an UPDATE command has been issued, + then the OK response also indicates that all pending database updates + have been sent to the client. That is, the slave can guarantee that + its local database is up to date as of a certain time by issuing a + NOOP and waiting for the OK. The OK MUST NOT return until all + updates that were pending at the time of the NOOP have been sent. + +4.9. Command: RESERVE + + The RESERVE command takes two parameters (just like the RESERVE + response), the mailbox name to reserve and location data. If the + server responds OK, then the mailbox name has been reserved. If the + server responds NO, then the mailbox name has not been reserved (for + + + +Siemborski Experimental [Page 10] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + + example, another server has reserved it already). This command MUST + NOT be issued to a slave. + + The typical sequence for mailbox creation is: + +C: R01 RESERVE "user.rjs3.new" "mail3.example.org!u4" +S: R01 OK "Mailbox Reserved." +<client does local mailbox create operations> +C: A01 ACTIVATE "user.rjs3.new" "mail3.example.org!u4" "rjs3 lrswipcda" +S: A01 OK "Mailbox Activated." + +4.10. Command: STARTTLS + + The STARTTLS command requests the commencement of a [TLS] + negotiation. The negotiation begins immediately after the CRLF in + the OK response. After a client issues a STARTTLS command, it MUST + NOT issue further commands until a server response is seen and the + [TLS] negotiation is complete. + + The STARTTLS command is only valid in non-authenticated state. The + server remains in non-authenticated state, even if client credentials + are supplied during the [TLS] negotiation. The [SASL] EXTERNAL + mechanism MAY be used to authenticate once [TLS] client credentials + are successfully exchanged. Note that servers are not required to + support the EXTERNAL mechanism. + + After the [TLS] layer is established, the server MUST re-issue the + initial response banner (see Section 3.8). This is necessary to + protect against man-in-the-middle attacks which alter the + capabilities list prior to STARTTLS, as well as to advertise any new + SASL mechanisms (or other capabilities) that may be available under + the layer. The client MUST discard cached capability information and + replace it with the new information. + + After the a successful STARTTLS command, the server SHOULD return a + NO response to additional STARTTLS commands. + + Servers MAY choose to not implement STARTTLS. In this case, they + MUST NOT advertise STARTTLS in their capabilities banner, and SHOULD + return a BAD response to the STARTTLS command, if it is issued. + + Example: + +C: S01 STARTTLS +S: S01 OK "Begin TLS negotiation now" +<TLS negotiation, further commands are under TLS layer> +S: * AUTH KERBEROS_V4 GSSAPI PLAIN +S: * OK MUPDATE "mupdate.example.org" "Cyrus" "v2.1.2" "(master)" + + + +Siemborski Experimental [Page 11] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + +4.11. Command: UPDATE + + The UPDATE command is how a slave initializes an update stream from + the master (though it is also valid to issue this command to a + slave). In response to the command, the server returns a list of all + mailboxes in its database (the same results as a parameterless LIST + command) followed by an OK response. From this point forward, + whenever an update occurs to the master database, it MUST stream the + update to the slave within 30 seconds. That is, it will send + RESERVE, MAILBOX, or DELETE responses as they are applicable. + + After a client has issued an UPDATE command, it may only issue NOOP + and LOGOUT commands for the remainder of the session. + + Example: + +C: U01 UPDATE +S: U01 MAILBOX "user.leg" "mail2.example.org!u1" "leg lrswipcda" +S: U01 MAILBOX "user.rjs3" "mail3.example.org!u4" "rjs3 lrswipcda" +S: U01 RESERVE "internet.bugtraq" "mail1.example.org!u5" "anyone lrs" +S: U01 OK "Streaming Begins" +<some time goes by, and another client creates a new mailbox> +S: U01 RESERVE "user.leg.new" "mail2.example.org!u1" +<some more time passes, and the create succeeds> +S: U01 MAILBOX "user.leg.new" "mail2.example.org!u1" "leg lrswipcda" +<much more time passes, and the slave decides to send a NOOP to reset +its inactivity timer> +C: N01 NOOP +S: U01 DELETE "user.leg.new" +S: N01 OK "NOOP Complete" + +5. MUPDATE Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [ABNF]. This uses the ABNF core + rules as specified in Appendix A of [ABNF]. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper or lower case characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + Note that this specification also uses some terminals from section 8 + of [ACAP]. + + cmd-activate = "ACTIVATE" SP string SP string SP string + + cmd-authenticate = "AUTHENTICATE" SP sasl-mech [ SP string ] + + + +Siemborski Experimental [Page 12] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + + cmd-delete = "DELETE" SP string + + cmd-find = "FIND" SP string + + cmd-list = "LIST" [ SP string ] + + cmd-logout = "LOGOUT" + + cmd-noop = "NOOP" + + cmd-reserve = "RESERVE" SP string SP string + + cmd-starttls = "STARTTLS" + + cmd-update = "UPDATE" + + command = tag SP command-type CRLF + + command-type = cmd-activate / cmd-authenticate / cmd-delete / + cmd-find / cmd-list / cmd-logout / cmd-noop / + cmd-reserve / cmd-starttls / cmd-update + + response = tag SP response-type CRLF + + response-type = rsp-ok / rsp-no / rsp-bad / rsp-bye / rsp-mailbox / + rsp-reserve / rsp-delete + + rsp-bad = "BAD" SP string + + rsp-bye = "BYE" SP string + + rsp-mailbox = "MAILBOX" SP string SP string SP string + + rsp-no = "NO" SP string + + rsp-ok = "OK" SP string + + rsp-reserve = "RESERVE" SP string SP string + + rsp-delete = "DELETE" SP string + + sasl-mech = 1*ATOM-CHAR + ; ATOM-CHAR is defined in [ACAP] + + string = quoted / literal + ; quoted and literal are defined in [ACAP] + + + + + +Siemborski Experimental [Page 13] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + + tag = 1*ATOM-CHAR + ; ATOM-CHAR is defined in [ACAP] + +6. MUPDATE URL Scheme + + This document defines the a URL scheme for the purposes of + referencing MUPDATE resources, according to the requirements in + [RFC2717]. This includes both MUPDATE servers as a whole, along with + individual mailbox entries on a given MUPDATE server. + + There is no MIME type associated with these resources. It is + intended that a URL consumer would either retrieve the MUPDATE record + in question, or simply connect to the MUPDATE server running on the + specified host. Note that the consumer will need to have + authentication credentials for the specified host. + + The MUPDATE URL scheme is similar to the IMAP URL scheme [IMAP-URL]. + However, it only takes one of two possible forms: + + mupdate://<iserver>/ + mupdate://<iserver>/<mailbox> + + The first form refers to a MUPDATE server as a whole, the second form + indicates both the server and a mailbox to run a FIND against once + authenticated to the server. Note that part of <iserver> may include + username and authentication information along with a hostname and + port. + +6.1. MUPDATE URL Scheme Registration Form + + URL scheme name: "mupdate" + + URL scheme syntax: + + This defines the MUPDATE URL Scheme in [ABNF]. Terminals from the + BNF of IMAP URLs [IMAP-URL] are also used. + + mupdateurl = "mupdate://" iserver "/" [ enc_mailbox ] + ; iserver and enc_mailbox are as defined in [IMAP-URL] + + Character encoding considerations: + + Identical to those described in [IMAP-URL] for the appropriate + terminals. + + + + + + + +Siemborski Experimental [Page 14] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + + Intended Usage: + + The form of the URL without an associated mailbox is intended to + designate a MUPDATE server only. If a mailbox name is included in + the URL, then the consumer is expected to execute a FIND command + for that mailbox on the specified server. + + Applications and/or protocols which use this URL scheme name: + + The protocol described in this document. + + Interoperability Considerations: + + None. + + Security Considerations: + + Users of the MUPDATE URL Scheme should review the security + considerations that are discussed in [IMAP-URL]. In particular, + the consequences of including authentication mechanism information + in a URL should be reviewed. + + Relevant Publications: + + This document and [IMAP-URL]. + + Author, Change Controller, and Contact for Further Information: + + Author of this document. + +7. Security Considerations + + While no unauthenticated users may make modifications or even perform + searches on the database, it is important to note that this + specification assumes no protections of any type for authenticated + users. + + All authenticated users have complete access to the database. For + this reason it is important to ensure that accounts that are making + use of the database are well secured. + + A more secure deployment might have all read only access go through a + slave, and only have accounts which need write access use the master. + This has the disadvantage of a marginally longer time for updates to + reach the clients. + + + + + + +Siemborski Experimental [Page 15] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + + The protocol assumes that all authenticated users are cooperating to + maintain atomic operations. Therefore, all new mailboxes SHOULD be + RESERVEd before they are ACTIVATEd, despite the fact that the + protocol does not require this, and it is therefore possible for a + set of participants which do not obey the provided locking to create + an inconsistent database. RESERVEing the mailbox first is not + required to perform an activate because this behavior simplifies + synchronization with the actual location of the mailboxes. + +8. IANA Considerations + + The IANA has assigned TCP port number 3905 to "mupdate". + + The IANA has registered a URL scheme for the MUPDATE protocol, as + defined in section 6.1 of this document. + + IANA has registered a GSSAPI service name of "mupdate" for the + MUPDATE protocol in the registry maintained at: + + http://www.iana.org/assignments/gssapi-service-names + +9. Intellectual Property Rights + + The IETF takes no position regarding the validity or scope of any + intellectual property or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; neither does it represent that it + has made any effort to identify any such rights. Information on the + IETF's procedures with respect to rights in standards-track and + standards-related documentation can be found in BCP-11. Copies of + claims of rights made available for publication and any assurances of + licenses to be made available, or the result of an attempt made to + obtain a general license or permission for the use of such + proprietary rights by implementors or users of this specification can + be obtained from the IETF Secretariat. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights which may cover technology that may be required to practice + this standard. Please address the information to the IETF Executive + Director. + + + + + + + + + +Siemborski Experimental [Page 16] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + +10. References + +10.1. Normative References + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [IMAP] Crispin, M., "Internet Message Access Protocol - Version + 4", RFC 3501, March 2003. + + [ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", RFC 2234, November 1997. + + [MIME] Freed, N. and N. Bornstein, "Multipurpose Internet Mail + Extensions (MIME) Part One: Format of Internet Message + Bodies", RFC 2045, November 1996. + + [IMAP-ACL] Myers, J., "IMAP4 ACL extension", RFC 2086, January 1997. + + [SASL] Myers, J., "Simple Authentication and Security Layer + (SASL)", RFC 2222, October 1997. + + [IMAP-URL] Newman, C., "IMAP URL Scheme", RFC 2192, September 1997. + + [ACAP] Newman, C. and J. Myers, "ACAP -- Application + Configuration Access Protocol", RFC 2244, November 1997. + + [TLS] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", + RFC 2246, January 1999. + +10.2. Informative References + + [POP3] Myers, J. and M. Rose, "Post Office Protocol - Version + 3", STD 53, RFC 1939, May 1996. + + [RFC2717] Petke, R. and I. King, "Registration Procedures for URL + Scheme Names", BCP 35, RFC 2717, November 1999. + + + + + + + + + + + + + + +Siemborski Experimental [Page 17] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + +11. Acknowledgments + + Lawrence Greenfield and Ken Murchison, for a great deal of input on + both the protocol and the text of the documents. + +12. Author's Address + + Robert Siemborski + Carnegie Mellon, Andrew Systems Group + Cyert Hall 207 + 5000 Forbes Avenue + Pittsburgh, PA 15213 + + Phone: (412) 268-7456 + EMail: rjs3+@andrew.cmu.edu + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Siemborski Experimental [Page 18] + +RFC 3656 MUPDATE Distributed Mailbox Database Protocol December 2003 + + +13. Full Copyright Statement + + Copyright (C) The Internet Society (2003). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assignees. + + This document and the information contained herein is provided on an + "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING + TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING + BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION + HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF + MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + + + + + + + + + + + + + +Siemborski Experimental [Page 19] + diff --git a/imap/docs/rfc/rfc3691.txt b/imap/docs/rfc/rfc3691.txt new file mode 100644 index 00000000..2f4e9b44 --- /dev/null +++ b/imap/docs/rfc/rfc3691.txt @@ -0,0 +1,283 @@ + + + + + + +Network Working Group A. Melnikov +Request for Comments: 3691 Isode Ltd. +Category: Standards Track February 2004 + + + Internet Message Access Protocol (IMAP) UNSELECT command + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2004). All Rights Reserved. + +Abstract + + This document defines an UNSELECT command that can be used to close + the current mailbox in an Internet Message Access Protocol - version + 4 (IMAP4) session without expunging it. Certain types of IMAP + clients need to release resources associated with the selected + mailbox without selecting a different mailbox. While IMAP4 provides + this functionality (via a SELECT command with a nonexistent mailbox + name or reselecting the same mailbox with EXAMINE command), a more + clean solution is desirable. + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 + 2. UNSELECT command . . . . . . . . . . . . . . . . . . . . . . . 2 + 3. Security Considerations. . . . . . . . . . . . . . . . . . . . 3 + 4. Formal Syntax. . . . . . . . . . . . . . . . . . . . . . . . . 3 + 5. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 3 + 6. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 3 + 7. Normative References . . . . . . . . . . . . . . . . . . . . . 4 + 8. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 4 + 9. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 5 + + + + + + + + + + +Melnikov Standards Track [Page 1] + +RFC 3691 IMAP UNSELECT command February 2004 + + +1. Introduction + + Certain types of IMAP clients need to release resources associated + with the selected mailbox without selecting a different mailbox. + While [IMAP4] provides this functionality (via a SELECT command with + a nonexistent mailbox name or reselecting the same mailbox with + EXAMINE command), a more clean solution is desirable. + + [IMAP4] defines the CLOSE command that closes the selected mailbox as + well as permanently removes all messages with the \Deleted flag set. + + However [IMAP4] lacks a command that simply closes the mailbox + without expunging it. This document defines the UNSELECT command for + this purpose. + + A server which supports this extension indicates this with a + capability name of "UNSELECT". + + "C:" and "S:" in examples show lines sent by the client and server + respectively. + + The keywords "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in + this document when typed in uppercase are to be interpreted as + defined in "Key words for use in RFCs to Indicate Requirement Levels" + [KEYWORDS]. + +2. UNSELECT Command + + Arguments: none + + Responses: no specific responses for this command + + Result: OK - unselect completed, now in authenticated state + BAD - no mailbox selected, or argument supplied but + none permitted + + The UNSELECT command frees server's resources associated with the + selected mailbox and returns the server to the authenticated + state. This command performs the same actions as CLOSE, except + that no messages are permanently removed from the currently + selected mailbox. + + Example: C: A341 UNSELECT + S: A341 OK Unselect completed + + + + + + + +Melnikov Standards Track [Page 2] + +RFC 3691 IMAP UNSELECT command February 2004 + + +3. Security Considerations + + It is believed that this extension doesn't raise any additional + security concerns not already discussed in [IMAP4]. + +4. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [ABNF]. Non-terminals + referenced but not defined below are as defined by [IMAP4]. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper or lower case characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + command-select /= "UNSELECT" + +5. IANA Considerations + + IMAP4 capabilities are registered by publishing a standards track or + IESG approved experimental RFC. The registry is currently located + at: + + http://www.iana.org/assignments/imap4-capabilities + + This document defines the UNSELECT IMAP capabilities. IANA has added + this capability to the registry. + +6. Acknowledgments + + UNSELECT command was originally implemented by Tim Showalter in Cyrus + IMAP server. + + Also, the author of the document would like to thank Vladimir Butenko + and Mark Crispin for reminding that UNSELECT has to be documented. + Also thanks to Simon Josefsson for pointing out that there are + multiple ways to implement UNSELECT. + + + + + + + + + + + + + +Melnikov Standards Track [Page 3] + +RFC 3691 IMAP UNSELECT command February 2004 + + +7. Normative References + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [IMAP4] Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 3501, March 2003. + + [ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 2234, November 1997. + +8. Author's Address + + Alexey Melnikov + Isode Limited + 5 Castle Business Village + Hampton, Middlesex TW12 2BX + + EMail: Alexey.Melnikov@isode.com + URI: http://www.melnikov.ca/ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov Standards Track [Page 4] + +RFC 3691 IMAP UNSELECT command February 2004 + + +9. Full Copyright Statement + + Copyright (C) The Internet Society (2004). This document is subject + to the rights, licenses and restrictions contained in BCP 78 and + except as set forth therein, the authors retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE + REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE + INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR + IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed + to pertain to the implementation or use of the technology + described in this document or the extent to which any license + under such rights might or might not be available; nor does it + represent that it has made any independent effort to identify any + such rights. Information on the procedures with respect to + rights in RFC documents can be found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use + of such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository + at http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention + any copyrights, patents or patent applications, or other + proprietary rights that may cover technology that may be required + to implement this standard. Please address the information to the + IETF at ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + + + +Melnikov Standards Track [Page 5] + diff --git a/imap/docs/rfc/rfc4314.txt b/imap/docs/rfc/rfc4314.txt new file mode 100644 index 00000000..e73a56f2 --- /dev/null +++ b/imap/docs/rfc/rfc4314.txt @@ -0,0 +1,1515 @@ + + + + + + +Network Working Group A. Melnikov +Request for Comments: 4314 Isode Ltd. +Obsoletes: 2086 December 2005 +Category: Standards Track + + + IMAP4 Access Control List (ACL) Extension + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2005). + +Abstract + + The Access Control List (ACL) extension (RFC 2086) of the Internet + Message Access Protocol (IMAP) permits mailbox access control lists + to be retrieved and manipulated through the IMAP protocol. + + This document is a revision of RFC 2086. It defines several new + access control rights and clarifies which rights are required for + different IMAP commands. + + + + + + + + + + + + + + + + + + + + + + +Melnikov Standards Track [Page 1] + +RFC 4314 IMAP ACL December 2005 + + +Table of Contents + + 1. Introduction and Overview .......................................3 + 1.1. Conventions Used in This Document ..........................3 + 2. Access Control ..................................................3 + 2.1. Standard Rights ............................................5 + 2.1.1. Obsolete Rights .....................................5 + 2.2. Rights Defined in RFC 2086 .................................8 + 3. Access control management commands and responses ................8 + 3.1. SETACL Command .............................................8 + 3.2. DELETEACL Command ..........................................9 + 3.3. GETACL Command ............................................10 + 3.4. LISTRIGHTS Command ........................................10 + 3.5. MYRIGHTS Command ..........................................11 + 3.6. ACL Response ..............................................11 + 3.7. LISTRIGHTS Response .......................................12 + 3.8. MYRIGHTS Response .........................................12 + 4. Rights Required to Perform Different IMAP4rev1 Commands ........12 + 5. Other Considerations ...........................................17 + 5.1. Additional Requirements and Implementation Notes ..........17 + 5.1.1. Servers ............................................17 + 5.1.2. Clients ............................................18 + 5.2. Mapping of ACL Rights to READ-WRITE and READ-ONLY + Response Codes ............................................19 + 6. Security Considerations ........................................20 + 7. Formal Syntax ..................................................21 + 8. IANA Considerations ............................................22 + 9. Internationalization Considerations ............................22 + Appendix A. Changes since RFC 2086 ................................23 + Appendix B. Compatibility with RFC 2086 ...........................24 + Appendix C. Known Deficiencies ....................................24 + Appendix D. Acknowledgements ......................................25 + Normative References ..............................................25 + Informative References ............................................25 + + + + + + + + + + + + + + + + + +Melnikov Standards Track [Page 2] + +RFC 4314 IMAP ACL December 2005 + + +1. Introduction and Overview + + The ACL (Access Control List) extension of the Internet Message + Access Protocol [IMAP4] permits mailbox access control lists to be + retrieved and manipulated through the IMAP protocol. + + This document is a revision of RFC 2086 [RFC2086]. It tries to + clarify different ambiguities in RFC 2086, in particular, the use of + UTF-8 [UTF-8] in access identifiers, which rights are required for + different IMAP4 commands, and how READ-WRITE/READ-ONLY response codes + are related to ACL. + +1.1. Conventions Used in This Document + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. + + In all examples "/" character is used as hierarchy separator. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [KEYWORDS]. + + The phrase "ACL server" is just a shortcut for saying "IMAP server + that supports ACL extension as defined in this document". + +2. Access Control + + The ACL extension is present in any IMAP4 implementation that returns + "ACL" as one of the supported capabilities to the CAPABILITY command. + + A server implementation conformant to this document MUST also return + rights (see below) not defined in Section 2.2 in the "RIGHTS=" + capability. + + An access control list is a set of <access identifier,rights> pairs. + An ACL applies to a mailbox name. + + Access identifier (or just "identifier") is a UTF-8 [UTF-8] string. + The identifier "anyone" is reserved to refer to the universal + identity (all authentications, including anonymous). All user name + strings accepted by the LOGIN or AUTHENTICATE commands to + authenticate to the IMAP server are reserved as identifiers for the + corresponding users. Identifiers starting with a dash ("-") are + reserved for "negative rights", described below. All other + identifier strings are interpreted in an implementation-defined + manner. + + + + +Melnikov Standards Track [Page 3] + +RFC 4314 IMAP ACL December 2005 + + + Rights is a string listing a (possibly empty) set of alphanumeric + characters, each character listing a set of operations that is being + controlled. Lowercase letters are reserved for "standard" rights, + listed in Section 2.1. (Note that for compatibility with deployed + clients and servers uppercase rights are not allowed.) The set of + standard rights can only be extended by a standards-track document. + Digits are reserved for implementation- or site-defined rights. + + An implementation MAY tie rights together or MAY force rights to + always or never be granted to particular identifiers. For example, + in an implementation that uses UNIX mode bits, the rights "swite" are + tied, the "a" right is always granted to the owner of a mailbox and + is never granted to another user. If rights are tied in an + implementation, the implementation must be conservative in granting + rights in response to SETACL commands--unless all rights in a tied + set are specified, none of that set should be included in the ACL + entry for that identifier. A client can discover the set of rights + that may be granted to a given identifier in the ACL for a given + mailbox name by using the LISTRIGHTS command. + + It is possible for multiple identifiers in an access control list to + apply to a given user. For example, an ACL may include rights to be + granted to the identifier matching the user, one or more + implementation-defined identifiers matching groups that include the + user, and/or the identifier "anyone". How these rights are combined + to determine the user's access is implementation defined. An + implementation may choose, for example, to use the union of the + rights granted to the applicable identifiers. An implementation may + instead choose, for example, to use only those rights granted to the + most specific identifier present in the ACL. A client can determine + the set of rights granted to the logged-in user for a given mailbox + name by using the MYRIGHTS command. + + When an identifier in an ACL starts with a dash ("-"), that indicates + that associated rights are to be removed from the identifier prefixed + by the dash. This is referred to as a "negative right". This + differs from DELETEACL in that a negative right is added to the ACL + and is a part of the calculation of the rights. + + Let's assume that an identifier "fred" refers to a user with login + "fred". If the identifier "-fred" is granted the "w" right, that + indicates that the "w" right is to be removed from users matching the + identifier "fred", even though the user "fred" might have the "w" + right as a consequence of some other identifier in the ACL. A + DELETEACL of "fred" simply deletes the identifier "fred" from the + ACL; it does not affect any rights that the user "fred" may get from + another entry in the ACL, in particular it doesn't affect rights + granted to the identifier "-fred". + + + +Melnikov Standards Track [Page 4] + +RFC 4314 IMAP ACL December 2005 + + + Server implementations are not required to support "negative right" + identifiers. + +2.1. Standard Rights + + The currently defined standard rights are (note that the list below + doesn't list all commands that use a particular right): + + l - lookup (mailbox is visible to LIST/LSUB commands, SUBSCRIBE + mailbox) + r - read (SELECT the mailbox, perform STATUS) + s - keep seen/unseen information across sessions (set or clear + \SEEN flag via STORE, also set \SEEN during APPEND/COPY/ + FETCH BODY[...]) + w - write (set or clear flags other than \SEEN and \DELETED via + STORE, also set them during APPEND/COPY) + i - insert (perform APPEND, COPY into mailbox) + p - post (send mail to submission address for mailbox, + not enforced by IMAP4 itself) + k - create mailboxes (CREATE new sub-mailboxes in any + implementation-defined hierarchy, parent mailbox for the new + mailbox name in RENAME) + x - delete mailbox (DELETE mailbox, old mailbox name in RENAME) + t - delete messages (set or clear \DELETED flag via STORE, set + \DELETED flag during APPEND/COPY) + e - perform EXPUNGE and expunge as a part of CLOSE + a - administer (perform SETACL/DELETEACL/GETACL/LISTRIGHTS) + +2.1.1. Obsolete Rights + + Due to ambiguity in RFC 2086, some existing RFC 2086 server + implementations use the "c" right to control the DELETE command. + Others chose to use the "d" right to control the DELETE command. For + the former group, let's define the "create" right as union of the "k" + and "x" rights, and the "delete" right as union of the "e" and "t" + rights. For the latter group, let's define the "create" rights as a + synonym to the "k" right, and the "delete" right as union of the "e", + "t", and "x" rights. + + For compatibility with RFC 2086, this section defines two virtual + rights "d" and "c". + + If a client includes the "d" right in a rights list, then it MUST be + treated as if the client had included every member of the "delete" + right. (It is not an error for a client to specify both the "d" + right and one or more members of the "delete" right, but the effect + is no different than if just the "d" right or all members of the + "delete" right had been specified.) + + + +Melnikov Standards Track [Page 5] + +RFC 4314 IMAP ACL December 2005 + + + When any of the "delete" member rights is set in a list of rights, + the server MUST also include the "d" right when returning the list in + a MYRIGHTS or ACL response. This is to enable older clients + conforming to RFC 2086 to work with newer servers. (*) + + Example: C: A001 SeTacl INBOX/Drafts David lrswida + S: A001 OK Setacl complete + + The client has specified the "d" right in the SETACL command above + and it expands to "et" on the server: + + C: A002 getacl INBOX/Drafts + S: * ACL INBOX Fred rwipslxcetda David lrswideta + S: A002 OK Getacl complete + + If the identifier specified in the LISTRIGHTS command can be granted + any of the "delete" member rights on a mailbox, then the server MUST + include the "d" right in the corresponding LISTRIGHTS response. (*) + If the member rights aren't tied to non-member rights, then the "d" + right is returned by itself in the LISTRIGHTS response. If any of + the member rights needs to be tied to one (or more) non-member right, + then the "d" right and all of the member rights need to be tied to + the same non-member right(s) (**). + + If a client includes the "c" right in a rights list, then it MUST be + treated as if the client had included every member of the "create" + right. (It is not an error for a client to specify both the "c" + right and one or more members of the "create" right, but the effect + is no different than if just the "c" right or all members of the + "create" right had been specified.) + + When any of the "create" member rights is set in a list of rights, + the server MUST also include the "c" right when returning the list in + a MYRIGHTS or ACL response. This is to enable older clients + conforming to RFC 2086 to work with newer servers. (*) + + Example: C: A003 Setacl INBOX/Drafts Byron lrswikda + S: A001 OK Setacl complete + C: A002 getAcl INBOX/Drafts + S: * ACL INBOX Fred rwipslxcetda Byron lrswikcdeta + S: A002 OK Getacl complete + + The client has specified the "d" right in the SETACL command above + and it expands to "et" on the server: As the client has specified the + "k" right (which is a member of the "c" right), the server also + returns the "c" right. + + + + + +Melnikov Standards Track [Page 6] + +RFC 4314 IMAP ACL December 2005 + + + If the identifier specified in the LISTRIGHTS command can be granted + any of the "create" member rights on a mailbox, then the server MUST + include the "c" right in the corresponding LISTRIGHTS response. (*) + If the member rights aren't tied to non-member rights, then the "c" + right is returned by itself in the LISTRIGHTS response. If any of + the member rights needs to be tied to one (or more) non-member right, + then the "c" right and all of the member rights need to be tied to + the same non-member right(s) (**). + + Example: The server that ties the rights as follows: + + lr s w i p k x t + + and c=k + + will return: + + S: * LISTRIGHTS archive/imap anyone "" + lr s w i p k x t c d + + Example: The server that ties the rights as follows: + + lr s w i p k xte + + and c=k + + will return: + + S: * LISTRIGHTS archive/imap anyone "" + lr s w i p k xte c d + + Example: The server that ties the rights as follows: + + lr s w i p k x te + + and c=k + + will return: + + S: * LISTRIGHTS archive/imap anyone "" + lr s w i p k c x te d + + Example: The server that ties the rights as follows: + + lr swte i p k x + + and c=kx + + + + +Melnikov Standards Track [Page 7] + +RFC 4314 IMAP ACL December 2005 + + + will return: + + S: * LISTRIGHTS archive/imap anyone "" + lr swted i p k x c + + (*) Clients conforming to this document MUST ignore the virtual "d" + and "c" rights in MYRIGHTS, ACL, and LISTRIGHTS responses. + + (**) The IMAPEXT Working Group has debated this issue in great length + and after reviewing existing ACL implementations concluded that + this is a reasonable restriction. + +2.2. Rights Defined in RFC 2086 + + The "RIGHTS=" capability MUST NOT include any of the rights defined + in RFC 2086: "l", "r", "s", "w", "i", "p", "a", "c", "d", and the + digits ("0" .. "9"). + +3. Access control management commands and responses + + Servers, when processing a command that has an identifier as a + parameter (i.e., any of SETACL, DELETEACL, and LISTRIGHTS commands), + SHOULD first prepare the received identifier using "SASLprep" profile + [SASLprep] of the "stringprep" algorithm [Stringprep]. If the + preparation of the identifier fails or results in an empty string, + the server MUST refuse to perform the command with a BAD response. + Note that Section 6 recommends additional identifier's verification + steps. + +3.1. SETACL Command + + Arguments: mailbox name + identifier + access right modification + + Data: no specific data for this command + + Result: OK - setacl completed + NO - setacl failure: can't set acl + BAD - arguments invalid + + The SETACL command changes the access control list on the specified + mailbox so that the specified identifier is granted permissions as + specified in the third argument. + + The third argument is a string containing an optional plus ("+") or + minus ("-") prefix, followed by zero or more rights characters. If + the string starts with a plus, the following rights are added to any + + + +Melnikov Standards Track [Page 8] + +RFC 4314 IMAP ACL December 2005 + + + existing rights for the identifier. If the string starts with a + minus, the following rights are removed from any existing rights for + the identifier. If the string does not start with a plus or minus, + the rights replace any existing rights for the identifier. + + Note that an unrecognized right MUST cause the command to return the + BAD response. In particular, the server MUST NOT silently ignore + unrecognized rights. + + Example: C: A001 GETACL INBOX/Drafts + S: * ACL INBOX/Drafts Fred rwipslxetad Chris lrswi + S: A001 OK Getacl complete + C: A002 SETACL INBOX/Drafts Chris +cda + S: A002 OK Setacl complete + C: A003 GETACL INBOX/Drafts + S: * ACL INBOX/Drafts Fred rwipslxetad Chris lrswicdakxet + S: A003 OK Getacl complete + + + C: A035 SETACL INBOX/Drafts John lrQswicda + S: A035 BAD Uppercase rights are not allowed + + + C: A036 SETACL INBOX/Drafts John lrqswicda + S: A036 BAD The q right is not supported + +3.2. DELETEACL Command + + Arguments: mailbox name + identifier + + Data: no specific data for this command + + Result: OK - deleteacl completed + NO - deleteacl failure: can't delete acl + BAD - arguments invalid + + The DELETEACL command removes any <identifier,rights> pair for the + specified identifier from the access control list for the specified + mailbox. + + Example: C: B001 getacl INBOX + S: * ACL INBOX Fred rwipslxetad -Fred wetd $team w + S: B001 OK Getacl complete + C: B002 DeleteAcl INBOX Fred + S: B002 OK Deleteacl complete + + + + + +Melnikov Standards Track [Page 9] + +RFC 4314 IMAP ACL December 2005 + + + C: B003 GETACL INBOX + S: * ACL INBOX -Fred wetd $team w + S: B003 OK Getacl complete + +3.3. GETACL Command + + Arguments: mailbox name + + Data: untagged responses: ACL + + Result: OK - getacl completed + NO - getacl failure: can't get acl + BAD - arguments invalid + + The GETACL command returns the access control list for mailbox in an + untagged ACL response. + + Some implementations MAY permit multiple forms of an identifier to + reference the same IMAP account. Usually, such implementations will + have a canonical form that is stored internally. An ACL response + caused by a GETACL command MAY include a canonicalized form of the + identifier that might be different from the one used in the + corresponding SETACL command. + + Example: C: A002 GETACL INBOX + S: * ACL INBOX Fred rwipsldexta + S: A002 OK Getacl complete + +3.4. LISTRIGHTS Command + + Arguments: mailbox name + identifier + + Data: untagged responses: LISTRIGHTS + + Result: OK - listrights completed + NO - listrights failure: can't get rights list + BAD - arguments invalid + + The LISTRIGHTS command takes a mailbox name and an identifier and + returns information about what rights can be granted to the + identifier in the ACL for the mailbox. + + Some implementations MAY permit multiple forms of an identifier to + reference the same IMAP account. Usually, such implementations will + have a canonical form that is stored internally. A LISTRIGHTS + + + + + +Melnikov Standards Track [Page 10] + +RFC 4314 IMAP ACL December 2005 + + + response caused by a LISTRIGHTS command MUST always return the same + form of an identifier as specified by the client. This is to allow + the client to correlate the response with the command. + + Example: C: a001 LISTRIGHTS ~/Mail/saved smith + S: * LISTRIGHTS ~/Mail/saved smith la r swicdkxte + S: a001 OK Listrights completed + + Example: C: a005 listrights archive/imap anyone + S: * LISTRIGHTS archive.imap anyone "" + l r s w i p k x t e c d a 0 1 2 3 4 5 6 7 8 9 + S: a005 Listrights successful + +3.5. MYRIGHTS Command + + Arguments: mailbox name + + Data: untagged responses: MYRIGHTS + + Result: OK - myrights completed + NO - myrights failure: can't get rights + BAD - arguments invalid + + The MYRIGHTS command returns the set of rights that the user has to + mailbox in an untagged MYRIGHTS reply. + + Example: C: A003 MYRIGHTS INBOX + S: * MYRIGHTS INBOX rwiptsldaex + S: A003 OK Myrights complete + +3.6. ACL Response + + Data: mailbox name + zero or more identifier rights pairs + + The ACL response occurs as a result of a GETACL command. The first + string is the mailbox name for which this ACL applies. This is + followed by zero or more pairs of strings; each pair contains the + identifier for which the entry applies followed by the set of rights + that the identifier has. + + Section 2.1.1 details additional server requirements related to + handling of the virtual "d" and "c" rights. + + + + + + + + +Melnikov Standards Track [Page 11] + +RFC 4314 IMAP ACL December 2005 + + +3.7. LISTRIGHTS Response + + Data: mailbox name + identifier + required rights + list of optional rights + + The LISTRIGHTS response occurs as a result of a LISTRIGHTS command. + The first two strings are the mailbox name and identifier for which + this rights list applies. Following the identifier is a string + containing the (possibly empty) set of rights the identifier will + always be granted in the mailbox. + + Following this are zero or more strings each containing a set of + rights the identifier can be granted in the mailbox. Rights + mentioned in the same string are tied together. The server MUST + either grant all tied rights to the identifier in the mailbox or + grant none. Section 2.1.1 details additional server requirements + related to handling of the virtual "d" and "c" rights. + + The same right MUST NOT be listed more than once in the LISTRIGHTS + command. + +3.8. MYRIGHTS Response + + Data: mailbox name + rights + + The MYRIGHTS response occurs as a result of a MYRIGHTS command. The + first string is the mailbox name for which these rights apply. The + second string is the set of rights that the client has. + + Section 2.1.1 details additional server requirements related to + handling of the virtual "d" and "c" rights. + +4. Rights Required to Perform Different IMAP4rev1 Commands + + Before executing a command, an ACL-compliant server MUST check which + rights are required to perform it. This section groups command by + functions they perform and list the rights required. It also gives + the detailed description of any special processing required. + + For the purpose of this section the UID counterpart of a command is + considered to be the same command, e.g., both UID COPY and COPY + commands require the same set of rights. + + + + + + +Melnikov Standards Track [Page 12] + +RFC 4314 IMAP ACL December 2005 + + + The table below summarizes different rights or their combinations + that are required in order to perform different IMAP operations. As + it is not always possible to express complex right checking and + interactions, the description after the table should be used as the + primary reference. + + +-------------------+---+---+---+---+---+---+---+---+---+---+---+---+ + |Operations\Rights | l | r | s | w | i | k | x | t | e | a |Any|Non| + +-------------------+---+---+---+---+---+---+---+---+---+---+---+---+ + | commands in authenticated state | + +-------------------------------------------------------------------+ + | LIST | + | | | | | | | | | | | | + | SUBSCRIBE | * | | | | | | | | | | | * | + | UNSUBSCRIBE | | | | | | | | | | | | + | + | LSUB | * | | | | | | | | | | | * | + |CREATE (for parent)| | | | | | + | | | | | | | + | DELETE | | ? | | | | | + | ? | ? | | | | + | RENAME | | | | | | + | + | | | | | | + | SELECT/EXAMINE | | + | | | | | | | | | | | + | STATUS | | + | | | | | | | | | | | + | SETACL/DELETEACL | | | | | | | | | | + | | | + | GETACL/LISTRIGHTS | | | | | | | | | | + | | | + | MYRIGHTS | | | | | | | | | | | + | | + | APPEND | | | ? | ? | + | | | ? | | | | | + +-------------------------------------------------------------------+ + | commands in selected state | + +-------------------------------------------------------------------+ + | COPY | | | ? | ? | + | | | ? | | | | | + | EXPUNGE | | | | | | | | | + | | | | + | CLOSE | | | | | | | | | ? | | | | + | FETCH | | | ? | | | | | | | | | | + | STORE flags | | | ? | ? | | | | ? | | | | | + +-------------------+---+---+---+---+---+---+---+---+---+---+---+---+ + + Note: for all commands in the selected state, the "r" is implied, + because it is required to SELECT/EXAMINE a mailbox. Servers are not + required to check presence of the "r" right once a mailbox is + successfully selected. + + Legend: + + - The right is required + * - Only one of the rights marked with * is required + (see description below) + ? - The right is OPTIONAL (see description below) + "Any" - at least one of the "l", "r", "i", "k", "x", "a" rights is + required + "Non" - No rights required to perform the command + + + + +Melnikov Standards Track [Page 13] + +RFC 4314 IMAP ACL December 2005 + + + Listing and subscribing/unsubscribing mailboxes: + LIST - "l" right is required. However, unlike other commands + (e.g., SELECT) the server MUST NOT return a NO response if it + can't list a mailbox. + Note that if the user has "l" right to a mailbox "A/B", but not to + its parent mailbox "A", the LIST command should behave as if the + mailbox "A" doesn't exist, for example: + + C: A777 LIST "" * + S: * LIST (\NoInferiors) "/" "A/B" + S: * LIST () "/" "C" + S: * LIST (\NoInferiors) "/" "C/D" + S: A777 OK LIST completed + + + SUBSCRIBE - "l" right is required only if the server checks for + mailbox existence when performing SUBSCRIBE. + + UNSUBSCRIBE - no rights required to perform this operation. + + LSUB - "l" right is required only if the server checks for mailbox + existence when performing SUBSCRIBE. However, unlike other + commands (e.g., SELECT) the server MUST NOT return a NO response + if it can't list a subscribed mailbox. + + Mailbox management: + CREATE - "k" right on a nearest existing parent mailbox. When a + new mailbox is created, it SHOULD inherit the ACL from the parent + mailbox (if one exists) in the defined hierarchy. + + DELETE - "x" right on the mailbox. Note that some servers don't + allow to delete a non-empty mailbox. If this is the case, the + user would also need "r", "e", and "t" rights, in order to open + the mailbox and empty it. + + The DELETE command MUST delete the ACL associated with the deleted + mailbox. + + RENAME - Moving a mailbox from one parent to another requires the + "x" right on the mailbox itself and the "k" right for the new + parent. For example, if the user wants to rename the mailbox + named "A/B/C" to "D/E", the user must have the "x" right for the + mailbox "A/B/C" and the "k" right for the mailbox "D". + The RENAME command SHOULD NOT change the ACLs on the renamed + mailbox and submailboxes. + + + + + + +Melnikov Standards Track [Page 14] + +RFC 4314 IMAP ACL December 2005 + + + Copying or appending messages: + Before performing a COPY/APPEND command, the server MUST check if + the user has "i" right for the target mailbox. If the user + doesn't have "i" right, the operation fails. Otherwise for each + copied/appended message the server MUST check if the user has + "t" right - when the message has \Deleted flag set + "s" right - when the message has \Seen flag set + "w" right - for all other message flags. + Only when the user has a particular right are the corresponding + flags stored for the newly created message. The server MUST NOT + fail a COPY/APPEND if the user has no rights to set a particular + flag. + + Example: C: A003 MYRIGHTS TargetMailbox + S: * MYRIGHTS TargetMailbox rwis + S: A003 OK Myrights complete + + C: A004 FETCH 1:3 (FLAGS) + S: * 1 FETCH (FLAGS (\Draft \Deleted) + S: * 2 FETCH (FLAGS (\Answered) + S: * 3 FETCH (FLAGS ($Forwarded \Seen) + S: A004 OK Fetch Completed + + C: A005 COPY 1:3 TargetMailbox + S: A005 OK Copy completed + + C: A006 SELECT TargetMailbox + ... + S: A006 Select Completed + + Let's assume that the copied messages received message numbers + 77:79. + + C: A007 FETCH 77:79 (FLAGS) + S: * 77 FETCH (FLAGS (\Draft)) + S: * 78 FETCH (FLAGS (\Answered)) + S: * 79 FETCH (FLAGS ($Forwarded \Seen)) + S: A007 OK Fetch Completed + + \Deleted flag was lost on COPY, as the user has no "t" right in + the target mailbox. + If the MYRIGHTS command with the tag A003 would have returned: + + S: * MYRIGHTS TargetMailbox rsti + + the response from the FETCH with the tag A007 would have been: + + C: A007 FETCH 77:79 (FLAGS) + + + +Melnikov Standards Track [Page 15] + +RFC 4314 IMAP ACL December 2005 + + + S: * 77 FETCH (FLAGS (\Deleted)) + S: * 78 FETCH (FLAGS ()) + S: * 79 FETCH (FLAGS (\Seen)) + S: A007 OK Fetch Completed + + In the latter case, \Answered, $Forwarded, and \Draft flags were + lost on COPY, as the user has no "w" right in the target mailbox. + + Expunging the selected mailbox: + EXPUNGE - "e" right on the selected mailbox. + + CLOSE - "e" right on the selected mailbox. If the server is + unable to expunge the mailbox because the user doesn't have the + "e" right, the server MUST ignore the expunge request, close the + mailbox, and return the tagged OK response. + + Fetch information about a mailbox and its messages: + SELECT/EXAMINE/STATUS - "r" right on the mailbox. + + FETCH - A FETCH request that implies setting \Seen flag MUST NOT + set it, if the current user doesn't have "s" right. + + Changing flags: + STORE - the server MUST check if the user has + "t" right - when the user modifies \Deleted flag + "s" right - when the user modifies \Seen flag + "w" right - for all other message flags. + STORE operation SHOULD NOT fail if the user has rights to modify + at least one flag specified in the STORE, as the tagged NO + response to a STORE command is not handled very well by deployed + clients. + + Changing ACLs: + SETACL/DELETEACL - "a" right on the mailbox. + + Reading ACLs: + GETACL - "a" right on the mailbox. + + MYRIGHTS - any of the following rights is required to perform the + operation: "l", "r", "i", "k", "x", "a". + + LISTRIGHTS - "a" right on the mailbox. + + + + + + + + + +Melnikov Standards Track [Page 16] + +RFC 4314 IMAP ACL December 2005 + + +5. Other Considerations + +5.1. Additional Requirements and Implementation Notes + +5.1.1. Servers + + This document defines an additional capability that is used to + announce the list of extra rights (excluding the ones defined in RFC + 2086) supported by the server. The set of rights MUST include "t", + "e", "x", and "k". Note that the extra rights can appear in any + order. + + Example: C: 1 capability + S: * CAPABILITY IMAP4REV1 STARTTLS LITERAL+ + ACL RIGHTS=texk + S: 1 OK completed + + Any server implementing an ACL extension MUST accurately reflect the + current user's rights in FLAGS and PERMANENTFLAGS responses. + + Example: C: A142 SELECT INBOX + S: * 172 EXISTS + S: * 1 RECENT + S: * OK [UNSEEN 12] Message 12 is first unseen + S: * OK [UIDVALIDITY 3857529045] UIDs valid + S: * OK [UIDNEXT 4392] Predicted next UID + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS (\Seen \Answered \Flagged \*)] L + S: A142 OK [READ-WRITE] SELECT completed + C: A143 MYRIGHTS INBOX + S: * MYRIGHTS INBOX lrwis + S: A143 OK completed + + Note that in order to get better performance the client MAY pipeline + SELECT and MYRIGHTS commands: + + C: A142 SELECT INBOX + C: A143 MYRIGHTS INBOX + S: * 172 EXISTS + S: * 1 RECENT + S: * OK [UNSEEN 12] Message 12 is first unseen + S: * OK [UIDVALIDITY 3857529045] UIDs valid + S: * OK [UIDNEXT 4392] Predicted next UID + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS (\Seen \Answered \Flagged \*)] L + S: A142 OK [READ-WRITE] SELECT completed + S: * MYRIGHTS INBOX lrwis + S: A143 OK completed + + + +Melnikov Standards Track [Page 17] + +RFC 4314 IMAP ACL December 2005 + + + Servers MAY cache the rights a user has on a mailbox when the mailbox + is selected, so that if a client's rights on a mailbox are changed + with SETACL or DELETEACL, commands specific to the selected state + (e.g., STORE, EXPUNGE) might not reflect the changed rights until the + mailbox is re-selected. If the server checks the rights on each + command, then it SHOULD send FLAGS and PERMANENTFLAGS responses if + they have changed. If such server detects that the user no longer + has read access to the mailbox, it MAY send an untagged BYE response + and close connection. It MAY also refuse to execute all commands + specific to the selected state until the mailbox is closed; however, + server implementors should note that most clients don't handle NO + responses very well. + + An ACL server MAY modify one or more ACLs for one or more identifiers + as a side effect of modifying the ACL specified in a + SETACL/DELETEACL. If the server does that, it MUST send untagged ACL + response(s) to notify the client about the changes made. + + An ACL server implementation MUST treat received ACL modification + commands as a possible ambiguity with respect to subsequent commands + affected by the ACL, as described in Section 5.5 of [IMAP4]. Hence a + pipeline SETACL + MYRIGHTS is an ambiguity with respect to the + server, meaning that the server must execute the SETACL command to + completion before the MYRIGHTS. However, clients are permitted to + send such a pipeline. + +5.1.2. Clients + + The following requirement is put on clients in order to allow for + future extensibility. A client implementation that allows a user to + read and update ACLs MUST preserve unrecognized rights that it + doesn't allow the user to change. That is, if the client + + 1) can read ACLs + and + 2) can update ACLs + but + 3) doesn't allow the user to change the rights the client doesn't + recognize, then it MUST preserve unrecognized rights. + + Otherwise the client could risk unintentionally removing permissions + it doesn't understand. + + + + + + + + + +Melnikov Standards Track [Page 18] + +RFC 4314 IMAP ACL December 2005 + + +5.2. Mapping of ACL Rights to READ-WRITE and READ-ONLY Response Codes + + A particular ACL server implementation MAY allow "shared multiuser + access" to some mailboxes. "Shared multiuser access" to a mailbox + means that multiple different users are able to access the same + mailbox, if they have proper access rights. "Shared multiuser + access" to the mailbox doesn't mean that the ACL for the mailbox is + currently set to allow access by multiple users. Let's denote a + "shared multiuser write access" as a "shared multiuser access" when a + user can be granted flag modification rights (any of "w", "s", or + "t"). + + Section 4 describes which rights are required for modifying different + flags. + + If the ACL server implements some flags as shared for a mailbox + (i.e., the ACL for the mailbox MAY be set up so that changes to those + flags are visible to another user), let's call the set of rights + associated with these flags (as described in Section 4) for that + mailbox collectively as "shared flag rights". Note that the "shared + flag rights" set MAY be different for different mailboxes. + + If the server doesn't support "shared multiuser write access" to a + mailbox or doesn't implement shared flags on the mailbox, "shared + flag rights" for the mailbox is defined to be the empty set. + + Example 1: Mailbox "banan" allows "shared multiuser write access" and + implements flags \Deleted, \Answered, and $MDNSent as + shared flags. "Shared flag rights" for the mailbox "banan" + is a set containing flags "t" (because system flag + \Deleted requires "t" right) and "w" (because both + \Answered and $MDNSent require "w" right). + + Example 2: Mailbox "apple" allows "shared multiuser write access" and + implements \Seen system flag as shared flag. "Shared flag + rights" for the mailbox "apple" contains "s" right + because system flag \Seen requires "s" right. + + Example 3: Mailbox "pear" allows "shared multiuser write access" and + implements flags \Seen, \Draft as shared flags. "Shared + flag rights" for the mailbox "apple" is a set containing + flags "s" (because system flag \Seen requires "s" right) + and "w" (because system flag \Draft requires "w" right). + + The server MUST include a READ-ONLY response code in the tagged OK + response to a SELECT command if none of the following rights is + granted to the current user: + + + + +Melnikov Standards Track [Page 19] + +RFC 4314 IMAP ACL December 2005 + + + "i", "e", and "shared flag rights"(***). + + The server SHOULD include a READ-WRITE response code in the tagged OK + response if at least one of the "i", "e", or "shared flag + rights"(***) is granted to the current user. + + (***) Note that a future extension to this document can extend the + list of rights that causes the server to return the READ-WRITE + response code. + + Example 1 (continued): The user that has "lrs" rights for the mailbox + "banan". The server returns READ-ONLY + response code on SELECT, as none of "iewt" + rights is granted to the user. + + Example 2 (continued): The user that has "rit" rights for the mailbox + "apple". The server returns READ-WRITE + response code on SELECT, as the user has "i" + right. + + Example 3 (continued): The user that has "rset" rights for the + mailbox "pear". The server returns READ-WRITE + response code on SELECT, as the user has "e" + and "s" rights. + +6. Security Considerations + + An implementation MUST make sure the ACL commands themselves do not + give information about mailboxes with appropriately restricted ACLs. + For example, when a user agent executes a GETACL command on a mailbox + that the user has no permission to LIST, the server would respond to + that request with the same error that would be used if the mailbox + did not exist, thus revealing no existence information, much less the + mailbox's ACL. + + IMAP clients implementing ACL that are able to modify ACLs SHOULD + warn a user that wants to give full access (or even just the "a" + right) to the special identifier "anyone". + + This document relies on [SASLprep] to describe steps required to + perform identifier canonicalization (preparation). The preparation + algorithm in SASLprep was specifically designed such that its output + is canonical, and it is well-formed. However, due to an anomaly + [PR29] in the specification of Unicode normalization, canonical + equivalence is not guaranteed for a select few character sequences. + Identifiers prepared with SASLprep can be stored and returned by an + ACL server. The anomaly affects ACL manipulation and evaluation of + identifiers containing the selected character sequences. These + + + +Melnikov Standards Track [Page 20] + +RFC 4314 IMAP ACL December 2005 + + + sequences, however, do not appear in well-formed text. In order to + address this problem, an ACL server MAY reject identifiers containing + sequences described in [PR29] by sending the tagged BAD response. + This is in addition to the requirement to reject identifiers that + fail SASLprep preparation as described in Section 3. + + Other security considerations described in [IMAP4] are relevant to + this document. In particular, ACL information is sent in the clear + over the network unless confidentiality protection is negotiated. + + This can be accomplished either by the use of STARTTLS, negotiated + privacy protection in the AUTHENTICATE command, or some other + protection mechanism. + +7. Formal Syntax + + Formal syntax is defined using ABNF [ABNF], extending the ABNF rules + in Section 9 of [IMAP4]. Elements not defined here can be found in + [ABNF] and [IMAP4]. + + Except as noted otherwise, all alphabetic characters are case + insensitive. The use of uppercase or lowercase characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + LOWER-ALPHA = %x61-7A ;; a-z + + acl-data = "ACL" SP mailbox *(SP identifier SP + rights) + + capability =/ rights-capa + ;;capability is defined in [IMAP4] + + command-auth =/ setacl / deleteacl / getacl / + listrights / myrights + ;;command-auth is defined in [IMAP4] + + deleteacl = "DELETEACL" SP mailbox SP identifier + + getacl = "GETACL" SP mailbox + + identifier = astring + + listrights = "LISTRIGHTS" SP mailbox SP identifier + + listrights-data = "LISTRIGHTS" SP mailbox SP identifier + SP rights *(SP rights) + + + + +Melnikov Standards Track [Page 21] + +RFC 4314 IMAP ACL December 2005 + + + mailbox-data =/ acl-data / listrights-data / myrights-data + ;;mailbox-data is defined in [IMAP4] + + mod-rights = astring + ;; +rights to add, -rights to remove + ;; rights to replace + + myrights = "MYRIGHTS" SP mailbox + + myrights-data = "MYRIGHTS" SP mailbox SP rights + + new-rights = 1*LOWER-ALPHA + ;; MUST include "t", "e", "x", and "k". + ;; MUST NOT include standard rights listed + ;; in section 2.2 + + rights = astring + ;; only lowercase ASCII letters and digits + ;; are allowed. + + rights-capa = "RIGHTS=" new-rights + ;; RIGHTS=... capability + + setacl = "SETACL" SP mailbox SP identifier + SP mod-rights + +8. IANA Considerations + + IMAP4 capabilities are registered by publishing a standards-track or + IESG-approved experimental RFC. The registry is currently located + at: + + http://www.iana.org/assignments/imap4-capabilities + + This document defines the RIGHTS= IMAP capability. IANA has added + this capability to the registry. + +9. Internationalization Considerations + + Section 3 states requirements on servers regarding + internationalization of identifiers. + + + + + + + + + + +Melnikov Standards Track [Page 22] + +RFC 4314 IMAP ACL December 2005 + + +Appendix A. Changes since RFC 2086 + + 1. Changed the charset of "identifier" from US-ASCII to UTF-8. + 2. Specified that mailbox deletion is controlled by the "x" right + and EXPUNGE is controlled by the "e" right. + 3. Added the "t" right that controls STORE \Deleted. Redefined the + "d" right to be a macro for "e", "t", and possibly "x". + 4. Added the "k" right that controls CREATE. Redefined the "c" + right to be a macro for "k" and possibly "x". + 5. Specified that the "a" right also controls DELETEACL. + 6. Specified that the "r" right also controls STATUS. + 7. Removed the requirement to check the "r" right for CHECK, SEARCH + and FETCH, as this is required for SELECT/EXAMINE to be + successful. + 8. LISTRIGHTS requires the "a" right on the mailbox (same as + SETACL). + 9. Deleted "PARTIAL", this is a deprecated feature of RFC 1730. + 10. Specified that the "w" right controls setting flags other than + \Seen and \Deleted on APPEND. Also specified that the "s" right + controls the \Seen flag and that the "t" right controls the + \Deleted flag. + 11. Specified that SUBSCRIBE is NOT allowed with the "r" right. + 12. Specified that the "l" right controls SUBSCRIBE. + 13. GETACL is NOT allowed with the "r" right, even though there are + several implementations that allows that. If a user only has + "r" right, GETACL can disclose information about identifiers + existing on the mail system. + 14. Clarified that RENAME requires the "k" right for the new parent + and the "x" right for the old name. + 15. Added new section that describes which rights are required + and/or checked when performing various IMAP commands. + 16. Added mail client security considerations when dealing with + special identifier "anyone". + 17. Clarified that negative rights are not the same as DELETEACL. + 18. Added "Compatibility with RFC 2086" section. + 19. Added section about mapping of ACL rights to READ-WRITE and + READ-ONLY response codes. + 20. Changed BNF to ABNF. + 21. Added "Implementation Notes" section. + 22. Updated "References" section. + 23. Added more examples. + 24. Clarified when the virtual "c" and "d" rights are returned in + ACL, MYRIGHTS, and LISTRIGHTS responses. + + + + + + + + +Melnikov Standards Track [Page 23] + +RFC 4314 IMAP ACL December 2005 + + +Appendix B. Compatibility with RFC 2086 + + This non-normative section gives guidelines as to how an existing RFC + 2086 server implementation may be updated to comply with this + document. + + This document splits the "d" right into several new different rights: + "t", "e", and possibly "x" (see Section 2.1.1 for more details). The + "d" right remains for backward-compatibility, but it is a virtual + right. There are two approaches for RFC 2086 server implementors to + handle the "d" right and the new rights that have replaced it: + + a. Tie "t", "e" (and possibly "x) together - almost no changes. + b. Implement separate "x", "t" and "e". Return the "d" right in a + MYRIGHTS response or an ACL response containing ACL information + when any of the "t", "e" (and "x") is granted. + + In a similar manner this document splits the "c" right into several + new different rights: "k" and possibly "x" (see Section 2.1.1 for + more details). The "c" right remains for backwards-compatibility but + it is a virtual right. Again, RFC 2086 server implementors can + choose to tie rights or to implement separate rights, as described + above. + + Also check Sections 5.1.1 and 5.1.2, as well as Appendix A, to see + other changes required. Server implementors should check which + rights are required to invoke different IMAP4 commands as described + in Section 4. + +Appendix C. Known Deficiencies + + This specification has some known deficiencies including: + + 1. This is inadequate to provide complete read-write access to + mailboxes protected by Unix-style rights bits because there is no + equivalent to "chown" and "chgrp" commands nor is there a good + way to discover such limitations are present. + 2. Because this extension leaves the specific semantics of how + rights are combined by the server as implementation defined, the + ability to build a user-friendly interface is limited. + 3. Users, groups, and special identifiers (e.g., anyone) exist in + the same namespace. + + The work-in-progress "ACL2" extension is intended to redesign this + extension to address these deficiencies without the constraint of + backward-compatibility and may eventually supercede this facility. + + + + + +Melnikov Standards Track [Page 24] + +RFC 4314 IMAP ACL December 2005 + + + However, RFC 2086 is deployed in multiple implementations so this + intermediate step, which fixes the straightforward deficiencies in a + backward-compatible fashion, is considered worthwhile. + +Appendix D. Acknowledgements + + This document is a revision of RFC 2086 written by John G. Myers. + + Editor appreciates comments received from Mark Crispin, Chris Newman, + Cyrus Daboo, John G. Myers, Dave Cridland, Ken Murchison, Steve Hole, + Vladimir Butenko, Larry Greenfield, Robert Siemborski, Harrie + Hazewinkel, Philip Guenther, Brian Candler, Curtis King, Lyndon + Nerenberg, Lisa Dusseault, Arnt Gulbrandsen, and other participants + of the IMAPEXT working group. + +Normative References + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 4234, October 2005. + + [IMAP4] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO + 10646", STD 63, RFC 3629, November 2003. + + [Stringprep] Hoffman, P. and M. Blanchet, "Preparation of + Internationalized Strings ("stringprep")", RFC 3454, + December 2002. + + [SASLprep] Zeilenga, K., "SASLprep: Stringprep Profile for User + Names and Passwords", RFC 4013, February 2005. + +Informative References + + [RFC2086] Myers, J., "IMAP4 ACL extension", RFC 2086, + January 1997. + + [PR29] "Public Review Issue #29: Normalization Issue", + February 2004, + <http://www.unicode.org/review/pr-29.html>. + + + + + + + +Melnikov Standards Track [Page 25] + +RFC 4314 IMAP ACL December 2005 + + +Author's Address + + Alexey Melnikov + Isode Ltd. + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + GB + + EMail: alexey.melnikov@isode.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov Standards Track [Page 26] + +RFC 4314 IMAP ACL December 2005 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2005). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at ietf- + ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + +Melnikov Standards Track [Page 27] + diff --git a/imap/docs/rfc/rfc4315.txt b/imap/docs/rfc/rfc4315.txt new file mode 100644 index 00000000..c026f422 --- /dev/null +++ b/imap/docs/rfc/rfc4315.txt @@ -0,0 +1,451 @@ + + + + + + +Network Working Group M. Crispin +Request for Comments: 4315 December 2005 +Obsoletes: 2359 +Category: Standards Track + + + Internet Message Access Protocol (IMAP) - UIDPLUS extension + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2005). + +Abstract + + The UIDPLUS extension of the Internet Message Access Protocol (IMAP) + provides a set of features intended to reduce the amount of time and + resources used by some client operations. The features in UIDPLUS + are primarily intended for disconnected-use clients. + +1. Introduction and Overview + + The UIDPLUS extension is present in any IMAP server implementation + that returns "UIDPLUS" as one of the supported capabilities to the + CAPABILITY command. + + The UIDPLUS extension defines an additional command. In addition, + this document recommends new status response codes in IMAP that + SHOULD be returned by all server implementations, regardless of + whether or not the UIDPLUS extension is implemented. + + The added facilities of the features in UIDPLUS are optimizations; + clients can provide equivalent functionality, albeit less + efficiently, by using facilities in the base protocol. + +1.1. Conventions Used in This Document + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. + + + + + +Crispin Standards Track [Page 1] + +RFC 4315 IMAP - UIDPLUS Extension December 2005 + + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "MAY", and "OPTIONAL" in this document are to + be interpreted as described in [KEYWORDS]. + + A "UID set" is similar to the [IMAP] sequence set; however, the "*" + value for a sequence number is not permitted. + +2. Additional Commands + + The following command definition is an extension to [IMAP] section + 6.4. + +2.1. UID EXPUNGE Command + + Arguments: sequence set + + Data: untagged responses: EXPUNGE + + Result: OK - expunge completed + NO - expunge failure (e.g., permission denied) + BAD - command unknown or arguments invalid + + The UID EXPUNGE command permanently removes all messages that both + have the \Deleted flag set and have a UID that is included in the + specified sequence set from the currently selected mailbox. If a + message either does not have the \Deleted flag set or has a UID + that is not included in the specified sequence set, it is not + affected. + + This command is particularly useful for disconnected use clients. + By using UID EXPUNGE instead of EXPUNGE when resynchronizing with + the server, the client can ensure that it does not inadvertantly + remove any messages that have been marked as \Deleted by other + clients between the time that the client was last connected and + the time the client resynchronizes. + + If the server does not support the UIDPLUS capability, the client + should fall back to using the STORE command to temporarily remove + the \Deleted flag from messages it does not want to remove, then + issuing the EXPUNGE command. Finally, the client should use the + STORE command to restore the \Deleted flag on the messages in + which it was temporarily removed. + + Alternatively, the client may fall back to using just the EXPUNGE + command, risking the unintended removal of some messages. + + + + + + +Crispin Standards Track [Page 2] + +RFC 4315 IMAP - UIDPLUS Extension December 2005 + + + Example: C: A003 UID EXPUNGE 3000:3002 + S: * 3 EXPUNGE + S: * 3 EXPUNGE + S: * 3 EXPUNGE + S: A003 OK UID EXPUNGE completed + +3. Additional Response Codes + + The following response codes are extensions to the response codes + defined in [IMAP] section 7.1. With limited exceptions, discussed + below, server implementations that advertise the UIDPLUS extension + SHOULD return these response codes. + + In the case of a mailbox that has permissions set so that the client + can COPY or APPEND to the mailbox, but not SELECT or EXAMINE it, the + server SHOULD NOT send an APPENDUID or COPYUID response code as it + would disclose information about the mailbox. + + In the case of a mailbox that has UIDNOTSTICKY status (as defined + below), the server MAY omit the APPENDUID or COPYUID response code as + it is not meaningful. + + If the server does not return the APPENDUID or COPYUID response + codes, the client can discover this information by selecting the + destination mailbox. The location of messages placed in the + destination mailbox by COPY or APPEND can be determined by using + FETCH and/or SEARCH commands (e.g., for Message-ID or some unique + marker placed in the message in an APPEND). + + APPENDUID + + Followed by the UIDVALIDITY of the destination mailbox and the UID + assigned to the appended message in the destination mailbox, + indicates that the message has been appended to the destination + mailbox with that UID. + + If the server also supports the [MULTIAPPEND] extension, and if + multiple messages were appended in the APPEND command, then the + second value is a UID set containing the UIDs assigned to the + appended messages, in the order they were transmitted in the + APPEND command. This UID set may not contain extraneous UIDs or + the symbol "*". + + Note: the UID set form of the APPENDUID response code MUST NOT + be used if only a single message was appended. In particular, + a server MUST NOT send a range such as 123:123. This is + because a client that does not support [MULTIAPPEND] expects + only a single UID and not a UID set. + + + +Crispin Standards Track [Page 3] + +RFC 4315 IMAP - UIDPLUS Extension December 2005 + + + UIDs are assigned in strictly ascending order in the mailbox + (refer to [IMAP], section 2.3.1.1) and UID ranges are as in + [IMAP]; in particular, note that a range of 12:10 is exactly + equivalent to 10:12 and refers to the sequence 10,11,12. + + This response code is returned in a tagged OK response to the + APPEND command. + + COPYUID + + Followed by the UIDVALIDITY of the destination mailbox, a UID set + containing the UIDs of the message(s) in the source mailbox that + were copied to the destination mailbox and containing the UIDs + assigned to the copied message(s) in the destination mailbox, + indicates that the message(s) have been copied to the destination + mailbox with the stated UID(s). + + The source UID set is in the order the message(s) were copied; the + destination UID set corresponds to the source UID set and is in + the same order. Neither of the UID sets may contain extraneous + UIDs or the symbol "*". + + UIDs are assigned in strictly ascending order in the mailbox + (refer to [IMAP], section 2.3.1.1) and UID ranges are as in + [IMAP]; in particular, note that a range of 12:10 is exactly + equivalent to 10:12 and refers to the sequence 10,11,12. + + This response code is returned in a tagged OK response to the COPY + command. + + UIDNOTSTICKY + + The selected mailbox is supported by a mail store that does not + support persistent UIDs; that is, UIDVALIDITY will be different + each time the mailbox is selected. Consequently, APPEND or COPY + to this mailbox will not return an APPENDUID or COPYUID response + code. + + This response code is returned in an untagged NO response to the + SELECT command. + + Note: servers SHOULD NOT have any UIDNOTSTICKY mail stores. + This facility exists to support legacy mail stores in which it + is technically infeasible to support persistent UIDs. This + should be avoided when designing new mail stores. + + + + + + +Crispin Standards Track [Page 4] + +RFC 4315 IMAP - UIDPLUS Extension December 2005 + + + Example: C: A003 APPEND saved-messages (\Seen) {297} + C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST) + C: From: Fred Foobar <foobar@example.com> + C: Subject: afternoon meeting + C: To: mooch@example.com + C: Message-Id: <B27397-0100000@example.com> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: Hello Joe, do you think we can meet at 3:30 tomorrow? + C: + S: A003 OK [APPENDUID 38505 3955] APPEND completed + C: A004 COPY 2:4 meeting + S: A004 OK [COPYUID 38505 304,319:320 3956:3958] Done + C: A005 UID COPY 305:310 meeting + S: A005 OK No matching messages, so nothing copied + C: A006 COPY 2 funny + S: A006 OK Done + C: A007 SELECT funny + S: * 1 EXISTS + S: * 1 RECENT + S: * OK [UNSEEN 1] Message 1 is first unseen + S: * OK [UIDVALIDITY 3857529045] Validity session-only + S: * OK [UIDNEXT 2] Predicted next UID + S: * NO [UIDNOTSTICKY] Non-persistent UIDs + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS (\Deleted \Seen)] Limited + S: A007 OK [READ-WRITE] SELECT completed + + In this example, A003 and A004 demonstrate successful appending and + copying to a mailbox that returns the UIDs assigned to the messages. + A005 is an example in which no messages were copied; this is because + in A003, we see that message 2 had UID 304, and message 3 had UID + 319; therefore, UIDs 305 through 310 do not exist (refer to section + 2.3.1.1 of [IMAP] for further explanation). A006 is an example of a + message being copied that did not return a COPYUID; and, as expected, + A007 shows that the mail store containing that mailbox does not + support persistent UIDs. + +4. Formal Syntax + + Formal syntax is defined using ABNF [ABNF], which extends the ABNF + rules defined in [IMAP]. The IMAP4 ABNF should be imported before + attempting to validate these rules. + + append-uid = uniqueid + + capability =/ "UIDPLUS" + + + +Crispin Standards Track [Page 5] + +RFC 4315 IMAP - UIDPLUS Extension December 2005 + + + command-select =/ uid-expunge + + resp-code-apnd = "APPENDUID" SP nz-number SP append-uid + + resp-code-copy = "COPYUID" SP nz-number SP uid-set SP uid-set + + resp-text-code =/ resp-code-apnd / resp-code-copy / "UIDNOTSTICKY" + ; incorporated before the expansion rule of + ; atom [SP 1*<any TEXT-CHAR except "]">] + ; that appears in [IMAP] + + uid-expunge = "UID" SP "EXPUNGE" SP sequence-set + + uid-set = (uniqueid / uid-range) *("," uid-set) + + uid-range = (uniqueid ":" uniqueid) + ; two uniqueid values and all values + ; between these two regards of order. + ; Example: 2:4 and 4:2 are equivalent. + + Servers that support [MULTIAPPEND] will have the following extension + to the above rules: + + append-uid =/ uid-set + ; only permitted if client uses [MULTIAPPEND] + ; to append multiple messages. + +5. Security Considerations + + The COPYUID and APPENDUID response codes return information about the + mailbox, which may be considered sensitive if the mailbox has + permissions set that permit the client to COPY or APPEND to the + mailbox, but not SELECT or EXAMINE it. + + Consequently, these response codes SHOULD NOT be issued if the client + does not have access to SELECT or EXAMINE the mailbox. + +6. IANA Considerations + + This document constitutes registration of the UIDPLUS capability in + the imap4-capabilities registry, replacing [RFC2359]. + +7. Normative References + + [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 4234, October 2005. + + + + + +Crispin Standards Track [Page 6] + +RFC 4315 IMAP - UIDPLUS Extension December 2005 + + + [IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - + VERSION 4rev1", RFC 3501, March 2003. + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [MULTIAPPEND] Crispin, M., "Internet Message Access Protocol (IMAP) - + MULTIAPPEND Extension", RFC 3502, March 2003. + +8. Informative References + + [RFC2359] Myers, J., "IMAP4 UIDPLUS extension", RFC 2359, June + 1998. + +9. Changes from RFC 2359 + + This document obsoletes [RFC2359]. However, it is based upon that + document, and takes substantial text from it (albeit with numerous + clarifications in wording). + + [RFC2359] implied that a server must always return COPYUID/APPENDUID + data; thus suggesting that in such cases the server should return + arbitrary data if the destination mailbox did not support persistent + UIDs. This document adds the UIDNOTSTICKY response code to indicate + that a mailbox does not support persistent UIDs, and stipulates that + a UIDPLUS server does not return COPYUID/APPENDUID data when the COPY + (or APPEND) destination mailbox has UIDNOTSTICKY status. + +Author's Address + + Mark R. Crispin + Networks and Distributed Computing + University of Washington + 4545 15th Avenue NE + Seattle, WA 98105-4527 + + Phone: (206) 543-5762 + EMail: MRC@CAC.Washington.EDU + + + + + + + + + + + + + +Crispin Standards Track [Page 7] + +RFC 4315 IMAP - UIDPLUS Extension December 2005 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2005). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at ietf- + ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + +Crispin Standards Track [Page 8] + diff --git a/imap/docs/rfc/rfc4422.txt b/imap/docs/rfc/rfc4422.txt new file mode 100644 index 00000000..049fa8c5 --- /dev/null +++ b/imap/docs/rfc/rfc4422.txt @@ -0,0 +1,1851 @@ + + + + + + +Network Working Group A. Melnikov, Ed. +Request for Comments: 4422 Isode Limited +Obsoletes: 2222 K. Zeilenga, Ed. +Category: Standards Track OpenLDAP Foundation + June 2006 + + + Simple Authentication and Security Layer (SASL) + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + The Simple Authentication and Security Layer (SASL) is a framework + for providing authentication and data security services in + connection-oriented protocols via replaceable mechanisms. It + provides a structured interface between protocols and mechanisms. + The resulting framework allows new protocols to reuse existing + mechanisms and allows old protocols to make use of new mechanisms. + The framework also provides a protocol for securing subsequent + protocol exchanges within a data security layer. + + This document describes how a SASL mechanism is structured, describes + how protocols include support for SASL, and defines the protocol for + carrying a data security layer over a connection. In addition, this + document defines one SASL mechanism, the EXTERNAL mechanism. + + This document obsoletes RFC 2222. + + + + + + + + + + + + + +Melnikov & Zeilenga Standards Track [Page 1] + +RFC 4422 SASL June 2006 + + +Table of Contents + + 1. Introduction ....................................................3 + 1.1. Document Audiences .........................................4 + 1.2. Relationship to Other Documents ............................4 + 1.3. Conventions ................................................5 + 2. Identity Concepts ...............................................5 + 3. The Authentication Exchange .....................................6 + 3.1. Mechanism Naming ...........................................8 + 3.2. Mechanism Negotiation ......................................9 + 3.3. Request Authentication Exchange ............................9 + 3.4. Challenges and Responses ...................................9 + 3.4.1. Authorization Identity String ......................10 + 3.5. Aborting Authentication Exchanges .........................10 + 3.6. Authentication Outcome ....................................11 + 3.7. Security Layers ...........................................12 + 3.8. Multiple Authentications ..................................12 + 4. Protocol Requirements ..........................................13 + 5. Mechanism Requirements .........................................16 + 6. Security Considerations ........................................18 + 6.1. Active Attacks ............................................19 + 6.1.1. Hijack Attacks .....................................19 + 6.1.2. Downgrade Attacks ..................................19 + 6.1.3. Replay Attacks .....................................20 + 6.1.4. Truncation Attacks .................................20 + 6.1.5. Other Active Attacks ...............................20 + 6.2. Passive Attacks ...........................................20 + 6.3. Re-keying .................................................21 + 6.4. Other Considerations ......................................21 + 7. IANA Considerations ............................................22 + 7.1. SASL Mechanism Registry ...................................22 + 7.2. Registration Changes ......................................26 + 8. References .....................................................26 + 8.1. Normative References ......................................26 + 8.2. Informative References ....................................27 + 9. Acknowledgements ...............................................28 + Appendix A. The SASL EXTERNAL Mechanism ..........................29 + A.1. EXTERNAL Technical Specification ..........................29 + A.2. SASL EXTERNAL Examples ....................................30 + A.3. Security Considerations ...................................31 + Appendix B. Changes since RFC 2222 ...............................31 + + + + + + + + + + +Melnikov & Zeilenga Standards Track [Page 2] + +RFC 4422 SASL June 2006 + + +1. Introduction + + The Simple Authentication and Security Layer (SASL) is a framework + for providing authentication and data security services in + connection-oriented protocols via replaceable mechanisms. SASL + provides a structured interface between protocols and mechanisms. + SASL also provides a protocol for securing subsequent protocol + exchanges within a data security layer. The data security layer can + provide data integrity, data confidentiality, and other services. + + SASL's design is intended to allow new protocols to reuse existing + mechanisms without requiring redesign of the mechanisms and allows + existing protocols to make use of new mechanisms without redesign of + protocols. + + SASL is conceptually a framework that provides an abstraction layer + between protocols and mechanisms as illustrated in the following + diagram. + + SMTP LDAP XMPP Other protocols ... + \ | | / + \ | | / + SASL abstraction layer + / | | \ + / | | \ + EXTERNAL GSSAPI PLAIN Other mechanisms ... + + It is through the interfaces of this abstraction layer that the + framework allows any protocol to utilize any mechanism. While this + layer does generally hide the particulars of protocols from + mechanisms and the particulars of mechanisms from protocols, this + layer does not generally hide the particulars of mechanisms from + protocol implementations. For example, different mechanisms require + different information to operate, some of them use password-based + authentication, some of then require realm information, others make + use of Kerberos tickets, certificates, etc. Also, in order to + perform authorization, server implementations generally have to + implement identity mapping between authentication identities, whose + form is mechanism specific, and authorization identities, whose form + is application protocol specific. Section 2 discusses identity + concepts. + + It is possible to design and implement this framework in ways that do + abstract away particulars of similar mechanisms. Such a framework + implementation, as well as mechanisms implementations, could be + designed not only to be shared by multiple implementations of a + particular protocol but to be shared by implementations of multiple + protocols. + + + +Melnikov & Zeilenga Standards Track [Page 3] + +RFC 4422 SASL June 2006 + + + The framework incorporates interfaces with both protocols and + mechanisms in which authentication exchanges are carried out. + Section 3 discusses SASL authentication exchanges. + + To use SASL, each protocol (amongst other items) provides a method + for identifying which mechanism is to be used, a method for exchange + of mechanism-specific server-challenges and client-responses, and a + method for communicating the outcome of the authentication exchange. + Section 4 discusses SASL protocol requirements. + + Each SASL mechanism defines (amongst other items) a series of + server-challenges and client-responses that provide authentication + services and negotiate data security services. Section 5 discusses + SASL mechanism requirements. + + Section 6 discusses security considerations. Section 7 discusses + IANA considerations. Appendix A defines the SASL EXTERNAL mechanism. + +1.1. Document Audiences + + This document is written to serve several different audiences: + + - protocol designers using this specification to support + authentication in their protocol, + + - mechanism designers that define new SASL mechanisms, and + + - implementors of clients or servers for those protocols that + support SASL. + + While the document organization is intended to allow readers to focus + on details relevant to their engineering, readers are encouraged to + read and understand all aspects of this document. + +1.2. Relationship to Other Documents + + This document obsoletes RFC 2222. It replaces all portions of RFC + 2222 excepting sections 7.1 (the KERBEROS_IV mechanism), 7.2 (the + GSSAPI mechanism), 7.3 (the SKEY mechanism). The KERBEROS_IV and + SKEY mechanisms are now viewed as obsolete and their specifications + provided in RFC 2222 are Historic. The GSSAPI mechanism is now + separately specified [SASL-GSSAPI]. + + Appendix B provides a summary of changes since RFC 2222. + + + + + + + +Melnikov & Zeilenga Standards Track [Page 4] + +RFC 4422 SASL June 2006 + + +1.3. Conventions + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in BCP 14 [RFC2119]. + + Character names in this document use the notation for code points and + names from the Unicode Standard [Unicode]. For example, the letter + "a" may be represented as either <U+0061> or <LATIN SMALL LETTER A>. + + Note: a glossary of terms used in Unicode can be found in [Glossary]. + Information on the Unicode character encoding model can be found in + [CharModel]. + + In examples, "C:" and "S:" indicate lines of data to be sent by the + client and server, respectively. Lines have been wrapped for + improved readability. + +2. Identity Concepts + + In practice, authentication and authorization may involve multiple + identities, possibly in different forms (simple username, Kerberos + principal, X.500 Distinguished Name, etc.), possibly with different + representations (e.g., ABNF-described UTF-8 encoded Unicode character + string, BER-encoded Distinguished Name). While technical + specifications often prescribe both the identity form and + representation used on the network, different identity forms and/or + representations may be (and often are) used within implementations. + How identities of different forms relate to each other is, generally, + a local matter. In addition, the forms and representations used + within an implementation are a local matter. + + However, conceptually, the SASL framework involves two identities: + + 1) an identity associated with the authentication credentials + (termed the authentication identity), and + + 2) an identity to act as (termed the authorization identity). + + SASL mechanism specifications describe the credential form(s) (e.g., + X.509 certificates, Kerberos tickets, simple username/password) used + to authenticate the client, including (where appropriate) the syntax + and semantics of authentication identities carried in the + credentials. SASL protocol specifications describe the identity + form(s) used in authorization and, in particular, prescribe the + syntax and semantics of the authorization identity character string + to be transferred by mechanisms. + + + + +Melnikov & Zeilenga Standards Track [Page 5] + +RFC 4422 SASL June 2006 + + + The client provides its credentials (which include or imply an + authentication identity) and, optionally, a character string + representing the requested authorization identity as part of the SASL + exchange. When this character string is omitted or empty, the client + is requesting to act as the identity associated with the credentials + (e.g., the user is requesting to act as the authentication identity). + + The server is responsible for verifying the client's credentials and + verifying that the identity it associates with the client's + credentials (e.g., the authentication identity) is allowed to act as + the authorization identity. A SASL exchange fails if either (or + both) of these verifications fails. (The SASL exchange may fail for + other reasons, such as service authorization failure.) + + However, the precise form(s) of the authentication identities (used + within the server in its verifications, or otherwise) and the precise + form(s) of the authorization identities (used in making authorization + decisions, or otherwise) are beyond the scope of SASL and this + specification. In some circumstances, the precise identity forms + used in some context outside of the SASL exchange may be dictated by + other specifications. For instance, an identity assumption + authorization (proxy authorization) policy specification may dictate + how authentication and authorization identities are represented in + policy statements. + +3. The Authentication Exchange + + Each authentication exchange consists of a message from the client to + the server requesting authentication via a particular mechanism, + followed by one or more pairs of challenges from the server and + responses from the client, followed by a message from the server + indicating the outcome of the authentication exchange. (Note: + exchanges may also be aborted as discussed in Section 3.5.) + + The following illustration provides a high-level overview of an + authentication exchange. + + C: Request authentication exchange + S: Initial challenge + C: Initial response + <additional challenge/response messages> + S: Outcome of authentication exchange + + If the outcome is successful and a security layer was negotiated, + this layer is then installed (see Section 3.7). This also applies to + the following illustrations. + + + + + +Melnikov & Zeilenga Standards Track [Page 6] + +RFC 4422 SASL June 2006 + + + Some mechanisms specify that the first data sent in the + authentication exchange is from the client to the server. Protocols + may provide an optional initial response field in the request message + to carry this data. Where the mechanism specifies that the first + data sent in the exchange is from the client to the server, the + protocol provides an optional initial response field, and the client + uses this field, the exchange is shortened by one round-trip: + + C: Request authentication exchange + Initial response + <additional challenge/response messages> + S: Outcome of authentication exchange + + Where the mechanism specifies that the first data sent in the + exchange is from the client to the server and this field is + unavailable or unused, the client request is followed by an empty + challenge. + + C: Request authentication exchange + S: Empty Challenge + C: Initial Response + <additional challenge/response messages> + S: Outcome of authentication exchange + + Should a client include an initial response in its request where the + mechanism does not allow the client to send data first, the + authentication exchange fails. + + Some mechanisms specify that the server is to send additional data to + the client when indicating a successful outcome. Protocols may + provide an optional additional data field in the outcome message to + carry this data. Where the mechanism specifies that the server is to + return additional data with the successful outcome, the protocol + provides an optional additional data field in the outcome message, + and the server uses this field, the exchange is shortened by one + round-trip: + + C: Request authentication exchange + S: Initial challenge + C: Initial response + <additional challenge/response messages> + S: Outcome of authentication exchange with + additional data with success + + Where the mechanism specifies that the server is to return additional + data to the client with a successful outcome and this field is + unavailable or unused, the additional data is sent as a challenge + whose response is empty. After receiving this response, the server + then indicates the successful outcome. + + + +Melnikov & Zeilenga Standards Track [Page 7] + +RFC 4422 SASL June 2006 + + + C: Request authentication exchange + S: Initial challenge + C: Initial response + <additional challenge/response messages> + S: Additional data challenge + C: Empty Response + S: Outcome of authentication exchange + + Where mechanisms specify that the first data sent in the exchange is + from the client to the server and additional data is sent to the + client along with indicating a successful outcome, and the protocol + provides fields supporting both, then the exchange takes two fewer + round-trips: + + C: Request authentication exchange + Initial response + <additional challenge/response messages> + S: Outcome of authentication exchange + with additional data with success + + instead of: + + C: Request authentication exchange + S: Empty Challenge + C: Initial Response + <additional challenge/response messages> + S: Additional data challenge + C: Empty Response + S: Outcome of authentication exchange + +3.1. Mechanism Naming + + SASL mechanisms are named by character strings, from 1 to 20 + characters in length, consisting of ASCII [ASCII] uppercase letters, + digits, hyphens, and/or underscores. In the following Augmented + Backus-Naur Form (ABNF) [RFC4234] grammar, the <sasl-mech> production + defines the syntax of a SASL mechanism name. + + sasl-mech = 1*20mech-char + mech-char = UPPER-ALPHA / DIGIT / HYPHEN / UNDERSCORE + ; mech-char is restricted to A-Z (uppercase only), 0-9, -, and _ + ; from ASCII character set. + + UPPER-ALPHA = %x41-5A ; A-Z (uppercase only) + DIGIT = %x30-39 ; 0-9 + HYPHEN = %x2D ; hyphen (-) + UNDERSCORE = %x5F ; underscore (_) + + SASL mechanism names are registered as discussed in Section 7.1. + + + +Melnikov & Zeilenga Standards Track [Page 8] + +RFC 4422 SASL June 2006 + + +3.2. Mechanism Negotiation + + Mechanism negotiation is protocol specific. + + Commonly, a protocol will specify that the server advertises + supported and available mechanisms to the client via some facility + provided by the protocol, and the client will then select the "best" + mechanism from this list that it supports and finds suitable. + + Note that the mechanism negotiation is not protected by the + subsequent authentication exchange and hence is subject to downgrade + attacks if not protected by other means. + + To detect downgrade attacks, a protocol can allow the client to + discover available mechanisms subsequent to the authentication + exchange and installation of data security layers with at least data + integrity protection. This allows the client to detect changes to + the list of mechanisms supported by the server. + +3.3. Request Authentication Exchange + + The authentication exchange is initiated by the client by requesting + authentication via a mechanism it specifies. The client sends a + message that contains the name of the mechanism to the server. The + particulars of the message are protocol specific. + + Note that the name of the mechanism is not protected by the + mechanism, and hence is subject to alteration by an attacker if not + integrity protected by other means. + + Where the mechanism is defined to allow the client to send data + first, and the protocol's request message includes an optional + initial response field, the client may include the response to the + initial challenge in the authentication request message. + +3.4. Challenges and Responses + + The authentication exchange involves one or more pairs of server- + challenges and client-responses, the particulars of which are + mechanism specific. These challenges and responses are enclosed in + protocol messages, the particulars of which are protocol specific. + + Through these challenges and responses, the mechanism may: + + - authenticate the client to the server, + + - authenticate the server to the client, + + + + +Melnikov & Zeilenga Standards Track [Page 9] + +RFC 4422 SASL June 2006 + + + - transfer an authorization identity string, + + - negotiate a security layer, and + + - provide other services. + + The negotiation of the security layer may involve negotiation of the + security services to be provided in the layer, how these services + will be provided, and negotiation of a maximum cipher-text buffer + size each side is able to receive in the layer (see Section 3.6). + + After receiving an authentication request or any client response, the + server may issue a challenge, abort the exchange, or indicate the + outcome of an exchange. After receiving a challenge, a client + mechanism may issue a response or abort the exchange. + +3.4.1. Authorization Identity String + + The authorization identity string is a sequence of zero or more + Unicode [Unicode] characters, excluding the NUL (U+0000) character, + representing the identity to act as. + + If the authorization identity string is absent, the client is + requesting to act as the identity the server associates with the + client's credentials. An empty string is equivalent to an absent + authorization identity. + + A non-empty authorization identity string indicates that the client + wishes to act as the identity represented by the string. In this + case, the form of identity represented by the string, as well as the + precise syntax and semantics of the string, is protocol specific. + + While the character encoding schema used to transfer the + authorization identity string in the authentication exchange is + mechanism specific, mechanisms are expected to be capable of carrying + the entire Unicode repertoire (with the exception of the NUL + character). + +3.5. Aborting Authentication Exchanges + + A client or server may desire to abort an authentication exchange if + it is unwilling or unable to continue (or enter into). + + A client may abort the authentication exchange by sending a message, + the particulars of which are protocol specific, to the server, + indicating that the exchange is aborted. The server may be required + by the protocol to return a message in response to the client's abort + message. + + + +Melnikov & Zeilenga Standards Track [Page 10] + +RFC 4422 SASL June 2006 + + + Likewise, a server may abort the authentication exchange by sending a + message, the particulars of which are protocol specific, to the + client, indicating that the exchange is aborted. + +3.6. Authentication Outcome + + At the conclusion of the authentication exchange, the server sends a + message, the particulars of which are protocol specific, to the + client indicating the outcome of the exchange. + + The outcome is not successful if + + - the authentication exchange failed for any reason, + + - the client's credentials could not be verified, + + - the server cannot associate an identity with the client's + credentials, + + - the client-provided authorization identity string is malformed, + + - the identity associated with the client's credentials is not + authorized to act as the requested authorization identity, + + - the negotiated security layer (or lack thereof) is not + suitable, or + + - the server is not willing to provide service to the client for + any reason. + + The protocol may include an optional additional data field in this + outcome message. This field can only include additional data when + the outcome is successful. + + If the outcome is successful and a security layer was negotiated, + this layer is then installed. If the outcome is unsuccessful, or a + security layer was not negotiated, any existing security is left in + place. + + The outcome message provided by the server can provide a way for the + client to distinguish between errors that are best dealt with by re- + prompting the user for her credentials, errors that are best dealt + with by telling the user to try again later, and errors where the + user must contact a system administrator for resolution (see the SYS + and AUTH POP Response Codes [RFC3206] specification for an example). + This distinction is particularly useful during scheduled server + maintenance periods as it reduces support costs. It is also + important that the server can be configured such that the outcome + + + +Melnikov & Zeilenga Standards Track [Page 11] + +RFC 4422 SASL June 2006 + + + message will not distinguish between a valid user with invalid + credentials and an invalid user. + +3.7. Security Layers + + SASL mechanisms may offer a wide range of services in security + layers. Typical services include data integrity and data + confidentiality. SASL mechanisms that do not provide a security + layer are treated as negotiating no security layer. + + If use of a security layer is negotiated in the authentication + protocol exchange, the layer is installed by the server after + indicating the outcome of the authentication exchange and installed + by the client upon receipt of the outcome indication. In both cases, + the layer is installed before transfer of further protocol data. The + precise position upon which the layer takes effect in the protocol + data stream is protocol specific. + + Once the security layer is in effect in the protocol data stream, it + remains in effect until either a subsequently negotiated security + layer is installed or the underlying transport connection is closed. + + When in effect, the security layer processes protocol data into + buffers of protected data. If at any time the security layer is + unable or unwilling to continue producing buffers protecting protocol + data, the underlying transport connection MUST be closed. If the + security layer is not able to decode a received buffer, the + underlying connection MUST be closed. In both cases, the underlying + transport connection SHOULD be closed gracefully. + + Each buffer of protected data is transferred over the underlying + transport connection as a sequence of octets prepended with a four- + octet field in network byte order that represents the length of the + buffer. The length of the protected data buffer MUST be no larger + than the maximum size that the other side expects. Upon the receipt + of a length field whose value is greater than the maximum size, the + receiver SHOULD close the connection, as this might be a sign of an + attack. + + The maximum size that each side expects is fixed by the mechanism, + either through negotiation or by its specification. + +3.8. Multiple Authentications + + Unless explicitly permitted in the protocol (as stated in the + protocol's technical specification), only one successful SASL + authentication exchange may occur in a protocol session. In this + + + + +Melnikov & Zeilenga Standards Track [Page 12] + +RFC 4422 SASL June 2006 + + + case, once an authentication exchange has successfully completed, + further attempts to initiate an authentication exchange fail. + + Where multiple successful SASL authentication exchanges are permitted + in the protocol, then in no case may multiple SASL security layers be + simultaneously in effect. If a security layer is in effect and a + subsequent SASL negotiation selects a second security layer, then the + second security layer replaces the first. If a security layer is in + effect and a subsequent SASL negotiation selects no security layer, + the original security layer remains in effect. + + Where multiple successful SASL negotiations are permitted in the + protocol, the effect of a failed SASL authentication exchange upon + the previously established authentication and authorization state is + protocol specific. The protocol's technical specification should be + consulted to determine whether the previous authentication and + authorization state remains in force, or changed to an anonymous + state, or otherwise was affected. Regardless of the protocol- + specific effect upon previously established authentication and + authorization state, the previously negotiated security layer remains + in effect. + +4. Protocol Requirements + + In order for a protocol to offer SASL services, its specification + MUST supply the following information: + + 1) A service name, to be selected from registry of "service" elements + for the Generic Security Service Application Program Interface + (GSSAPI) host-based service name form, as described in Section 4.1 + of [RFC2743]. Note that this registry is shared by all GSSAPI and + SASL mechanisms. + + 2) Detail any mechanism negotiation facility that the protocol + provides (see Section 3.2). + + A protocol SHOULD specify a facility through which the client may + discover, both before initiation of the SASL exchange and after + installing security layers negotiated by the exchange, the names + of the SASL mechanisms that the server makes available to the + client. The latter is important to allow the client to detect + downgrade attacks. This facility is typically provided through + the protocol's extensions or capabilities discovery facility. + + 3) Definition of the messages necessary for authentication exchange, + including the following: + + + + + +Melnikov & Zeilenga Standards Track [Page 13] + +RFC 4422 SASL June 2006 + + + a) A message to initiate the authentication exchange (see Section + 3.3). + + This message MUST contain a field for carrying the name of the + mechanism selected by the client. + + This message SHOULD contain an optional field for carrying an + initial response. If the message is defined with this field, + the specification MUST describe how messages with an empty + initial response are distinguished from messages with no + initial response. This field MUST be capable of carrying + arbitrary sequences of octets (including zero-length sequences + and sequences containing zero-valued octets). + + b) Messages to transfer server challenges and client responses + (see Section 3.4). + + Each of these messages MUST be capable of carrying arbitrary + sequences of octets (including zero-length sequences and + sequences containing zero-valued octets). + + c) A message to indicate the outcome of the authentication + exchange (see Section 3.6). + + This message SHOULD contain an optional field for carrying + additional data with a successful outcome. If the message is + defined with this field, the specification MUST describe how + messages with an empty additional data are distinguished from + messages with no additional data. This field MUST be capable + of carrying arbitrary sequences of octets (including zero- + length sequences and sequences containing zero-valued octets). + + 4) Prescribe the syntax and semantics of non-empty authorization + identity strings (see Section 3.4.1). + + In order to avoid interoperability problems due to differing + normalizations, the protocol specification MUST detail precisely + how and where (client or server) non-empty authorization identity + strings are prepared, including all normalizations, for comparison + and other applicable functions to ensure proper function. + + Specifications are encouraged to prescribe use of existing + authorization identity forms as well as existing string + representations, such as simple user names [RFC4013]. + + Where the specification does not precisely prescribe how + identities in SASL relate to identities used elsewhere in the + protocol, for instance, in access control policy statements, it + + + +Melnikov & Zeilenga Standards Track [Page 14] + +RFC 4422 SASL June 2006 + + + may be appropriate for the protocol to provide a facility by which + the client can discover information (such as the representation of + the identity used in making access control decisions) about + established identities for these uses. + + 5) Detail any facility the protocol provides that allows the client + and/or server to abort authentication exchange (see Section 3.5). + + Protocols that support multiple authentications typically allow a + client to abort an ongoing authentication exchange by initiating a + new authentication exchange. Protocols that do not support + multiple authentications may require the client to close the + connection and start over to abort an ongoing authentication + exchange. + + Protocols typically allow the server to abort ongoing + authentication exchanges by returning a non-successful outcome + message. + + 6) Identify precisely where newly negotiated security layers start to + take effect, in both directions (see Section 3.7). + + Typically, specifications require security layers to start taking + effect on the first octet following the outcome message in data + being sent by the server and on the first octet sent after receipt + of the outcome message in data being sent by the client. + + 7) If the protocol supports other layered security services, such as + Transport Layer Security (TLS) [RFC4346], the specification MUST + prescribe the order in which security layers are applied to + protocol data. + + For instance, where a protocol supports both TLS and SASL security + layers, the specification could prescribe any of the following: + + a) SASL security layer is always applied first to data being sent + and, hence, applied last to received data, + + b) SASL security layer is always applied last to data being sent + and, hence, applied first to received data, + + c) Layers are applied in the order in which they were installed, + + d) Layers are applied in the reverse order in which they were + installed, or + + e) Both TLS and SASL security layers cannot be installed. + + + + +Melnikov & Zeilenga Standards Track [Page 15] + +RFC 4422 SASL June 2006 + + + 8) Indicate whether the protocol supports multiple authentications + (see Section 3.8). If so, the protocol MUST detail the effect a + failed SASL authentication exchange will have upon a previously + established authentication and authorization state. + + Protocol specifications SHOULD avoid stating implementation + requirements that would hinder replacement of applicable mechanisms. + In general, protocol specifications SHOULD be mechanism neutral. + There are a number of reasonable exceptions to this recommendation, + including + + - detailing how credentials (which are mechanism specific) are + managed in the protocol, + + - detailing how authentication identities (which are mechanism + specific) and authorization identities (which are protocol + specific) relate to each other, and + + - detailing which mechanisms are applicable to the protocol. + +5. Mechanism Requirements + + SASL mechanism specifications MUST supply the following information: + + 1) The name of the mechanism (see Section 3.1). This name MUST be + registered as discussed in Section 7.1. + + 2) A definition of the server-challenges and client-responses of the + authentication exchange, as well as the following: + + a) An indication of whether the mechanism is client-first, + variable, or server-first. If a SASL mechanism is defined as + client-first and the client does not send an initial response + in the authentication request, then the first server challenge + MUST be empty (the EXTERNAL mechanism is an example of this + case). If a SASL mechanism is defined as variable, then the + specification needs to state how the server behaves when the + initial client response in the authentication request is + omitted (the DIGEST-MD5 mechanism [DIGEST-MD5] is an example of + this case). If a SASL mechanism is defined as server-first, + then the client MUST NOT send an initial client response in the + authentication request (the CRAM-MD5 mechanism [CRAM-MD5] is an + example of this case). + + b) An indication of whether the server is expected to provide + additional data when indicating a successful outcome. If so, + if the server sends the additional data as a challenge, the + + + + +Melnikov & Zeilenga Standards Track [Page 16] + +RFC 4422 SASL June 2006 + + + specification MUST indicate that the response to this challenge + is an empty response. + + SASL mechanisms SHOULD be designed to minimize the number of + challenges and responses necessary to complete the exchange. + + 3) An indication of whether the mechanism is capable of transferring + authorization identity strings (see Section 3.4.1). While some + legacy mechanisms are incapable of transmitting an authorization + identity (which means that for these mechanisms, the authorization + identity is always the empty string), newly defined mechanisms + SHOULD be capable of transferring authorization identity strings. + The mechanism SHOULD NOT be capable of transferring both no + authorization identity string and an empty authorization identity. + + Mechanisms that are capable of transferring an authorization + identity string MUST be capable of transferring arbitrary non- + empty sequences of Unicode characters, excluding those that + contain the NUL (U+0000) character. Mechanisms SHOULD use the + UTF-8 [RFC3629] transformation format. The specification MUST + detail how any Unicode code points special to the mechanism that + might appear in the authorization identity string are escaped to + avoid ambiguity during decoding of the authorization identity + string. Typically, mechanisms that have special characters + require these special characters to be escaped or encoded in the + character string (after encoding it in a particular Unicode + transformation format) using a data encoding scheme such as Base64 + [RFC3548]. + + 4) The specification MUST detail whether the mechanism offers a + security layer. If the mechanism does, the specification MUST + detail the security and other services offered in the layer as + well as how these services are to be implemented. + + 5) If the underlying cryptographic technology used by a mechanism + supports data integrity, then the mechanism specification MUST + integrity protect the transmission of an authorization identity + and the negotiation of the security layer. + + SASL mechanisms SHOULD be protocol neutral. + + SASL mechanisms SHOULD reuse existing credential and identity forms, + as well as associated syntaxes and semantics. + + SASL mechanisms SHOULD use the UTF-8 transformation format [RFC3629] + for encoding Unicode [Unicode] code points for transfer. + + + + + +Melnikov & Zeilenga Standards Track [Page 17] + +RFC 4422 SASL June 2006 + + + In order to avoid interoperability problems due to differing + normalizations, when a mechanism calls for character data (other than + the authorization identity string) to be used as input to a + cryptographic and/or comparison function, the specification MUST + detail precisely how and where (client or server) the character data + is to be prepared, including all normalizations, for input into the + function to ensure proper operation. + + For simple user names and/or passwords in authentication credentials, + SASLprep [RFC4013] (a profile of the StringPrep [RFC3454] preparation + algorithm), SHOULD be specified as the preparation algorithm. + + The mechanism SHOULD NOT use the authorization identity string in + generation of any long-term cryptographic keys or hashes as there is + no requirement that the authorization identity string be canonical. + Long-term, here, means a term longer than the duration of the + authentication exchange in which they were generated. That is, as + different clients (of the same or different protocol) may provide + different authorization identity strings that are semantically + equivalent, use of authorization identity strings in generation of + cryptographic keys and hashes will likely lead to interoperability + and other problems. + +6. Security Considerations + + Security issues are discussed throughout this memo. + + Many existing SASL mechanisms do not provide adequate protection + against passive attacks, let alone active attacks, in the + authentication exchange. Many existing SASL mechanisms do not offer + security layers. It is hoped that future SASL mechanisms will + provide strong protection against passive and active attacks in the + authentication exchange, as well as security layers with strong basic + data security features (e.g., data integrity and data + confidentiality) services. It is also hoped that future mechanisms + will provide more advanced data security services like re-keying (see + Section 6.3). + + Regardless, the SASL framework is susceptible to downgrade attacks. + Section 6.1.2 offers a variety of approaches for preventing or + detecting these attacks. In some cases, it is appropriate to use + data integrity protective services external to SASL (e.g., TLS) to + protect against downgrade attacks in SASL. Use of external + protective security services is also important when the mechanisms + available do not themselves offer adequate integrity and/or + confidentiality protection of the authentication exchange and/or + protocol data. + + + + +Melnikov & Zeilenga Standards Track [Page 18] + +RFC 4422 SASL June 2006 + + +6.1. Active Attacks + +6.1.1. Hijack Attacks + + When the client selects a SASL security layer with at least integrity + protection, this protection serves as a counter-measure against an + active attacker hijacking the connection and modifying protocol data + sent after establishment of the security layer. Implementations + SHOULD close the connection when the security services in a SASL + security layer report protocol data report lack of data integrity. + +6.1.2. Downgrade Attacks + + It is important that any security-sensitive protocol negotiations be + performed after installation of a security layer with data integrity + protection. Protocols should be designed such that negotiations + performed prior to this installation should be revalidated after + installation is complete. Negotiation of the SASL mechanism is + security sensitive. + + When a client negotiates the authentication mechanism with the server + and/or other security features, it is possible for an active attacker + to cause a party to use the least secure security services available. + For instance, an attacker can modify the server-advertised mechanism + list or can modify the client-advertised security feature list within + a mechanism response. To protect against this sort of attack, + implementations SHOULD NOT advertise mechanisms and/or features that + cannot meet their minimum security requirements, SHOULD NOT enter + into or continue authentication exchanges that cannot meet their + minimum security requirements, and SHOULD verify that completed + authentication exchanges result in security services that meet their + minimum security requirements. Note that each endpoint needs to + independently verify that its security requirements are met. + + In order to detect downgrade attacks to the least (or less) secure + mechanism supported, the client can discover the SASL mechanisms that + the server makes available both before the SASL authentication + exchange and after the negotiated SASL security layer (with at least + data integrity protection) has been installed through the protocol's + mechanism discovery facility. If the client finds that the + integrity-protected list (the list obtained after the security layer + was installed) contains a stronger mechanism than those in the + previously obtained list, the client should assume that the + previously obtained list was modified by an attacker and SHOULD close + the underlying transport connection. + + The client's initiation of the SASL exchange, including the selection + of a SASL mechanism, is done in the clear and may be modified by an + + + +Melnikov & Zeilenga Standards Track [Page 19] + +RFC 4422 SASL June 2006 + + + active attacker. It is important for any new SASL mechanisms to be + designed such that an active attacker cannot obtain an authentication + with weaker security properties by modifying the SASL mechanism name + and/or the challenges and responses. + + Multi-level negotiation of security features is prone to downgrade + attack. Protocol designers should avoid offering higher-level + negotiation of security features in protocols (e.g., above SASL + mechanism negotiation) and mechanism designers should avoid lower- + level negotiation of security features in mechanisms (e.g., below + SASL mechanism negotiation). + +6.1.3. Replay Attacks + + Some mechanisms may be subject to replay attacks unless protected by + external data security services (e.g., TLS). + +6.1.4. Truncation Attacks + + Most existing SASL security layers do not themselves offer protection + against truncation attack. In a truncation attack, the active + attacker causes the protocol session to be closed, causing a + truncation of the possibly integrity-protected data stream that leads + to behavior of one or both the protocol peers that inappropriately + benefits the attacker. Truncation attacks are fairly easy to defend + against in connection-oriented application-level protocols. A + protocol can defend against these attacks by ensuring that each + information exchange has a clear final result and that each protocol + session has a graceful closure mechanism, and that these are + integrity protected. + +6.1.5. Other Active Attacks + + When use of a security layer is negotiated by the authentication + protocol exchange, the receiver SHOULD handle gracefully any + protected data buffer larger than the defined/negotiated maximal + size. In particular, it MUST NOT blindly allocate the amount of + memory specified in the buffer size field, as this might cause the + "out of memory" condition. If the receiver detects a large block, it + SHOULD close the connection. + +6.2. Passive Attacks + + Many mechanisms are subject to various passive attacks, including + simple eavesdropping of unprotected credential information as well as + online and offline dictionary attacks of protected credential + information. + + + + +Melnikov & Zeilenga Standards Track [Page 20] + +RFC 4422 SASL June 2006 + + +6.3. Re-keying + + The secure or administratively permitted lifetimes of SASL + mechanisms' security layers are finite. Cryptographic keys weaken as + they are used and as time passes; the more time and/or cipher-text + that a cryptanalyst has after the first use of the a key, the easier + it is for the cryptanalyst to mount attacks on the key. + + Administrative limits on a security layer's lifetime may take the + form of time limits expressed in X.509 certificates, in Kerberos V + tickets, or in directories, and are often desired. In practice, one + likely effect of administrative lifetime limits is that applications + may find that security layers stop working in the middle of + application protocol operation, such as, perhaps, during large data + transfers. As the result of this, the connection will be closed (see + Section 3.7), which will result in an unpleasant user experience. + + Re-keying (key renegotiation process) is a way of addressing the + weakening of cryptographic keys. The SASL framework does not itself + provide for re-keying; SASL mechanisms may. Designers of future SASL + mechanisms should consider providing re-keying services. + + Implementations that wish to re-key SASL security layers where the + mechanism does not provide for re-keying SHOULD reauthenticate the + same IDs and replace the expired or soon-to-expire security layers. + This approach requires support for reauthentication in the + application protocols (see Section 3.8). + +6.4. Other Considerations + + Protocol designers and implementors should understand the security + considerations of mechanisms so they may select mechanisms that are + applicable to their needs. + + Distributed server implementations need to be careful in how they + trust other parties. In particular, authentication secrets should + only be disclosed to other parties that are trusted to manage and use + those secrets in a manner acceptable to the disclosing party. + Applications using SASL assume that SASL security layers providing + data confidentiality are secure even when an attacker chooses the + text to be protected by the security layer. Similarly, applications + assume that the SASL security layer is secure even if the attacker + can manipulate the cipher-text output of the security layer. New + SASL mechanisms are expected to meet these assumptions. + + + + + + + +Melnikov & Zeilenga Standards Track [Page 21] + +RFC 4422 SASL June 2006 + + + Unicode security considerations [UTR36] apply to authorization + identity strings, as well as UTF-8 [RFC3629] security considerations + where UTF-8 is used. SASLprep [RFC4013] and StringPrep [RFC3454] + security considerations also apply where used. + +7. IANA Considerations + +7.1. SASL Mechanism Registry + + The SASL mechanism registry is maintained by IANA. The registry is + currently available at <http://www.iana.org/assignments/sasl- + mechanisms>. + + The purpose of this registry is not only to ensure uniqueness of + values used to name SASL mechanisms, but also to provide a definitive + reference to technical specifications detailing each SASL mechanism + available for use on the Internet. + + There is no naming convention for SASL mechanisms; any name that + conforms to the syntax of a SASL mechanism name can be registered. + + The procedure detailed in Section 7.1.1 is to be used for + registration of a value naming a specific individual mechanism. + + The procedure detailed in Section 7.1.2 is to be used for + registration of a value naming a family of related mechanisms. + + Comments may be included in the registry as discussed in Section + 7.1.3 and may be changed as discussed in Section 7.1.4. + + The SASL mechanism registry has been updated to reflect that this + document provides the definitive technical specification for SASL and + that this section provides the registration procedures for this + registry. + + + + + + + + + + + + + + + + + +Melnikov & Zeilenga Standards Track [Page 22] + +RFC 4422 SASL June 2006 + + +7.1.1. Mechanism Name Registration Procedure + + IANA will register new SASL mechanism names on a First Come First + Served basis, as defined in BCP 26 [RFC2434]. IANA has the right to + reject obviously bogus registration requests, but will perform no + review of claims made in the registration form. + + Registration of a SASL mechanism is requested by filling in the + following template: + + Subject: Registration of SASL mechanism X + + SASL mechanism name (or prefix for the family): + + Security considerations: + + Published specification (recommended): + + Person & email address to contact for further information: + + Intended usage: (One of COMMON, LIMITED USE, or OBSOLETE) + + Owner/Change controller: + + Note: (Any other information that the author deems relevant may be + added here.) + + and sending it via electronic mail to IANA at <iana@iana.org>. + + While this registration procedure does not require expert review, + authors of SASL mechanisms are encouraged to seek community review + and comment whenever that is feasible. Authors may seek community + review by posting a specification of their proposed mechanism as an + Internet-Draft. SASL mechanisms intended for widespread use should + be standardized through the normal IETF process, when appropriate. + + + + + + + + + + + + + + + + +Melnikov & Zeilenga Standards Track [Page 23] + +RFC 4422 SASL June 2006 + + +7.1.2. Family Name Registration Procedure + + As noted above, there is no general naming convention for SASL + mechanisms. However, specifications may reserve a portion of the + SASL mechanism namespace for a set of related SASL mechanisms, a + "family" of SASL mechanisms. Each family of SASL mechanisms is + identified by a unique prefix, such as X-. Registration of new SASL + mechanism family names requires expert review as defined in BCP 26 + [RFC2434]. + + Registration of a SASL family name is requested by filling in the + following template: + + Subject: Registration of SASL mechanism family X + + SASL family name (or prefix for the family): + + Security considerations: + + Published specification (recommended): + + Person & email address to contact for further information: + + Intended usage: (One of COMMON, LIMITED USE, or OBSOLETE) + + Owner/Change controller: + + Note: (Any other information that the author deems relevant may be + added here.) + + and sending it via electronic mail to the IETF SASL mailing list at + <ietf-sasl@imc.org> and carbon copying IANA at <iana@iana.org>. + After allowing two weeks for community input on the IETF SASL mailing + list, the expert will determine the appropriateness of the + registration request and either approve or disapprove the request + with notice to the requestor, the mailing list, and IANA. + + The review should focus on the appropriateness of the requested + family name for the proposed use and the appropriateness of the + proposed naming and registration plan for existing and future + mechanism names in the family. The scope of this request review may + entail consideration of relevant aspects of any provided technical + specification, such as their IANA Considerations section. However, + this review is narrowly focused on the appropriateness of the + requested registration and not on the overall soundness of any + provided technical specification. + + + + + +Melnikov & Zeilenga Standards Track [Page 24] + +RFC 4422 SASL June 2006 + + + Authors are encouraged to pursue community review by posting the + technical specification as an Internet-Draft and soliciting comment + by posting to appropriate IETF mailing lists. + +7.1.3. Comments on SASL Mechanism Registrations + + Comments on a registered SASL mechanism/family should first be sent + to the "owner" of the mechanism/family and/or to the <ietf- + sasl@imc.org> mailing list. + + Submitters of comments may, after a reasonable attempt to contact the + owner, request IANA to attach their comment to the SASL mechanism + registration itself by sending mail to <iana@iana.org>. At IANA's + sole discretion, IANA may attach the comment to the SASL mechanism's + registration. + +7.1.4. Change Control + + Once a SASL mechanism registration has been published by IANA, the + author may request a change to its definition. The change request + follows the same procedure as the registration request. + + The owner of a SASL mechanism may pass responsibility for the SASL + mechanism to another person or agency by informing IANA; this can be + done without discussion or review. + + The IESG may reassign responsibility for a SASL mechanism. The most + common case of this will be to enable changes to be made to + mechanisms where the author of the registration has died, has moved + out of contact, or is otherwise unable to make changes that are + important to the community. + + SASL mechanism registrations may not be deleted; mechanisms that are + no longer believed appropriate for use can be declared OBSOLETE by a + change to their "intended usage" field; such SASL mechanisms will be + clearly marked in the lists published by IANA. + + The IESG is considered to be the owner of all SASL mechanisms that + are on the IETF standards track. + + + + + + + + + + + + +Melnikov & Zeilenga Standards Track [Page 25] + +RFC 4422 SASL June 2006 + + +7.2. Registration Changes + + The IANA has updated the SASL mechanisms registry as follows: + + 1) Changed the "Intended usage" of the KERBEROS_V4 and SKEY mechanism + registrations to OBSOLETE. + + 2) Changed the "Published specification" of the EXTERNAL mechanism to + this document as indicated below: + + Subject: Updated Registration of SASL mechanism EXTERNAL + Family of SASL mechanisms: NO + SASL mechanism name: EXTERNAL + Security considerations: See A.3 of RFC 4422 + Published specification (optional, recommended): RFC 4422 + Person & email address to contact for further information: + Alexey Melnikov <Alexey.Melnikov@isode.com> + Intended usage: COMMON + Owner/Change controller: IESG <iesg@ietf.org> + Note: Updates existing entry for EXTERNAL + +8. References + +8.1. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2244] Newman, C. and J. G. Myers, "ACAP -- Application + Configuration Access Protocol", RFC 2244, November + 1997. + + [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing + an IANA Considerations Section in RFCs", BCP 26, RFC + 2434, October 1998. + + [RFC2743] Linn, J., "Generic Security Service Application Program + Interface Version 2, Update 1", RFC 2743, January 2000. + + [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of + Internationalized Strings ("stringprep")", RFC 3454, + December 2002. + + [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO + 10646", STD 63, RFC 3629, November 2003. + + [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User + Names and Passwords", RFC 4013, February 2005. + + + +Melnikov & Zeilenga Standards Track [Page 26] + +RFC 4422 SASL June 2006 + + + [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 4234, October 2005. + + [ASCII] Coded Character Set--7-bit American Standard Code for + Information Interchange, ANSI X3.4-1986. + + [Unicode] The Unicode Consortium, "The Unicode Standard, Version + 3.2.0" is defined by "The Unicode Standard, Version + 3.0" (Reading, MA, Addison-Wesley, 2000. ISBN 0-201- + 61633-5), as amended by the "Unicode Standard Annex + #27: Unicode 3.1" + (http://www.unicode.org/reports/tr27/) and by the + "Unicode Standard Annex #28: Unicode 3.2" + (http://www.unicode.org/reports/tr28/). + + [CharModel] Whistler, K. and M. Davis, "Unicode Technical Report + #17, Character Encoding Model", UTR17, + <http://www.unicode.org/unicode/reports/tr17/>, August + 2000. + + [Glossary] The Unicode Consortium, "Unicode Glossary", + <http://www.unicode.org/glossary/>. + +8.2. Informative References + + [RFC3206] Gellens, R., "The SYS and AUTH POP Response Codes", RFC + 3206, February 2002. + + [RFC3548] Josefsson, S., "The Base16, Base32, and Base64 Data + Encodings", RFC 3548, July 2003. + + [RFC4301] Kent, S. and K. Seo, "Security Architecture for the + Internet Protocol", RFC 4301, December 2005. + + [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer + Security (TLS) Protocol Version 1.1", RFC 4346, April + 2006. + + [SASL-GSSAPI] Melnikov, A. (Editor), "The Kerberos V5 ("GSSAPI") SASL + Mechanism", Work in Progress, May 2006. + + [UTR36] Davis, M., "(Draft) Unicode Technical Report #36, + Character Encoding Model", UTR17, + <http://www.unicode.org/unicode/reports/tr36/>, + February 2005. + + [CRAM-MD5] Nerenberg, L., "The CRAM-MD5 SASL Mechanism", Work in + Progress. + + + +Melnikov & Zeilenga Standards Track [Page 27] + +RFC 4422 SASL June 2006 + + + [DIGEST-MD5] Leach, P., C. Newman, and A. Melnikov, "Using Digest + Authentication as a SASL Mechanism", Work in Progress, + March 2006. + +9. Acknowledgements + + This document is a revision of RFC 2222 written by John Myers. + + This revision is a product of the IETF Simple Authentication and + Security Layer (SASL) Working Group. + + The following individuals contributed significantly to this revision: + Abhijit Menon-Sen, Hallvard Furuseth, Jeffrey Hutzelman, John Myers, + Luke Howard, Magnus Nystrom, Nicolas Williams, Peter Saint-Andre, RL + 'Bob' Morgan, Rob Siemborski, Sam Hartman, Simon Josefsson, Tim + Alsop, and Tony Hansen. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov & Zeilenga Standards Track [Page 28] + +RFC 4422 SASL June 2006 + + +Appendix A. The SASL EXTERNAL Mechanism + + This appendix is normative. + + The EXTERNAL mechanism allows a client to request the server to use + credentials established by means external to the mechanism to + authenticate the client. The external means may be, for instance, IP + Security [RFC4301] or TLS [RFC4346] services. In absence of some a + priori agreement between the client and the server, the client cannot + make any assumption as to what external means the server has used to + obtain the client's credentials, nor make an assumption as to the + form of credentials. For example, the client cannot assume that the + server will use the credentials the client has established via TLS. + +A.1. EXTERNAL Technical Specification + + The name of this mechanism is "EXTERNAL". + + The mechanism does not provide a security layer. + + The mechanism is capable of transferring an authorization identity + string. If empty, the client is requesting to act as the identity + the server has associated with the client's credentials. If non- + empty, the client is requesting to act as the identity represented by + the string. + + The client is expected to send data first in the authentication + exchange. Where the client does not provide an initial response data + in its request to initiate the authentication exchange, the server is + to respond to the request with an empty initial challenge and then + the client is to provide its initial response. + + The client sends the initial response containing the UTF-8 [RFC3629] + encoding of the requested authorization identity string. This + response is non-empty when the client is requesting to act as the + identity represented by the (non-empty) string. This response is + empty when the client is requesting to act as the identity the server + associated with its authentication credentials. + + The syntax of the initial response is specified as a value of the + <extern-initial-resp> production detailed below using the Augmented + Backus-Naur Form (ABNF) [RFC4234] notation. + + external-initial-resp = authz-id-string + authz-id-string = *( UTF8-char-no-nul ) + UTF8-char-no-nul = UTF8-1-no-nul / UTF8-2 / UTF8-3 / UTF8-4 + UTF8-1-no-nul = %x01-7F + + + + +Melnikov & Zeilenga Standards Track [Page 29] + +RFC 4422 SASL June 2006 + + + where the <UTF8-2>, <UTF8-3>, and <UTF8-4> productions are as defined + in [RFC3629]. + + There are no additional challenges and responses. + + Hence, the server is to return the outcome of the authentication + exchange. + + The exchange fails if + + - the client has not established its credentials via external means, + + - the client's credentials are inadequate, + + - the client provided an empty authorization identity string and the + server is unwilling or unable to associate an authorization + identity with the client's credentials, + + - the client provided a non-empty authorization identity string that + is invalid per the syntax requirements of the applicable + application protocol specification, + + - the client provided a non-empty authorization identity string + representing an identity that the client is not allowed to act as, + or + + - the server is unwilling or unable to provide service to the client + for any other reason. + + Otherwise the exchange is successful. When indicating a successful + outcome, additional data is not provided. + +A.2. SASL EXTERNAL Examples + + This section provides examples of EXTERNAL authentication exchanges. + The examples are intended to help the readers understand the above + text. The examples are not definitive. The Application + Configuration Access Protocol (ACAP) [RFC2244] is used in the + examples. + + The first example shows use of EXTERNAL with an empty authorization + identity. In this example, the initial response is not sent in the + client's request to initiate the authentication exchange. + + S: * ACAP (SASL "DIGEST-MD5") + C: a001 STARTTLS + S: a001 OK "Begin TLS negotiation now" + <TLS negotiation, further commands are under TLS layer> + + + +Melnikov & Zeilenga Standards Track [Page 30] + +RFC 4422 SASL June 2006 + + + S: * ACAP (SASL "DIGEST-MD5" "EXTERNAL") + C: a002 AUTHENTICATE "EXTERNAL" + S: + "" + C: + "" + S: a002 OK "Authenticated" + + The second example shows use of EXTERNAL with an authorization + identity of "fred@example.com". In this example, the initial + response is sent with the client's request to initiate the + authentication exchange. This saves a round-trip. + + S: * ACAP (SASL "DIGEST-MD5") + C: a001 STARTTLS + S: a001 OK "Begin TLS negotiation now" + <TLS negotiation, further commands are under TLS layer> + S: * ACAP (SASL "DIGEST-MD5" "EXTERNAL") + C: a002 AUTHENTICATE "EXTERNAL" {16+} + C: fred@example.com + S: a002 NO "Cannot assume requested authorization identity" + +A.3. Security Considerations + + The EXTERNAL mechanism provides no security protection; it is + vulnerable to spoofing by either client or server, active attack, and + eavesdropping. It should only be used when adequate security + services have been established. + +Appendix B. Changes since RFC 2222 + + This appendix is non-normative. + + The material in RFC 2222 was significantly rewritten in the + production of this document. + + RFC 2222, by not stating that the authorization identity string was a + string of Unicode characters, let alone character data, implied that + the authorization identity string was a string of octets. + + - The authorization identity string is now defined as a string of + Unicode characters. The NUL (U+0000) character is prohibited. + While protocol specifications are responsible for defining the + authorization identity form, as well as the Unicode string syntax + and related semantics, mechanism specifications are responsible + for defining how the Unicode string is carried in the + authentication exchange. + + - Deleted "If so, when the client does not send data first, the + initial challenge MUST be specified as being an empty challenge." + + + +Melnikov & Zeilenga Standards Track [Page 31] + +RFC 4422 SASL June 2006 + + + The following technical change was made to the EXTERNAL mechanism: + + - The authorization identity string is to be UTF-8 encoded. + + Note that protocol and mechanism specification requirements have + been significantly tightened. Existing protocol and mechanism + specifications will need to be updated to meet these requirements. + +Editors' Addresses + + Alexey Melnikov + Isode Limited + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex, + TW12 2BX, United Kingdom + + EMail: Alexey.Melnikov@isode.com + URI: http://www.melnikov.ca/ + + + Kurt D. Zeilenga + OpenLDAP Foundation + + EMail: Kurt@OpenLDAP.org + + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov & Zeilenga Standards Track [Page 32] + +RFC 4422 SASL June 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + + + +Melnikov & Zeilenga Standards Track [Page 33] + diff --git a/imap/docs/rfc/rfc4466.txt b/imap/docs/rfc/rfc4466.txt new file mode 100644 index 00000000..dfde1685 --- /dev/null +++ b/imap/docs/rfc/rfc4466.txt @@ -0,0 +1,955 @@ + + + + + + +Network Working Group A. Melnikov +Request for Comments: 4466 Isode Ltd. +Updates: 2088, 2342, 3501, 3502, 3516 C. Daboo +Category: Standards Track April 2006 + + + Collected Extensions to IMAP4 ABNF + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + Over the years, many documents from IMAPEXT and LEMONADE working + groups, as well as many individual documents, have added syntactic + extensions to many base IMAP commands described in RFC 3501. For + ease of reference, this document collects most of such ABNF changes + in one place. + + This document also suggests a set of standard patterns for adding + options and extensions to several existing IMAP commands defined in + RFC 3501. The patterns provide for compatibility between existing + and future extensions. + + This document updates ABNF in RFCs 2088, 2342, 3501, 3502, and 3516. + It also includes part of the errata to RFC 3501. This document + doesn't specify any semantic changes to the listed RFCs. + + + + + + + + + + + + + + + +Melnikov & Daboo Standards Track [Page 1] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + +Table of Contents + + 1. Introduction ....................................................2 + 1.1. Purpose of This Document ...................................2 + 1.2. Conventions Used in This Document ..........................3 + 2. IMAP ABNF Extensions ............................................3 + 2.1. Optional Parameters with the SELECT/EXAMINE Commands .......3 + 2.2. Extended CREATE Command ....................................4 + 2.3. Extended RENAME Command ....................................5 + 2.4. Extensions to FETCH and UID FETCH Commands .................6 + 2.5. Extensions to STORE and UID STORE Commands .................6 + 2.6. Extensions to SEARCH Command ...............................7 + 2.6.1. Extended SEARCH Command .............................7 + 2.6.2. ESEARCH untagged response ...........................8 + 2.7. Extensions to APPEND Command ...............................8 + 3. Formal Syntax ...................................................9 + 4. Security Considerations ........................................14 + 5. Normative References ...........................................15 + 6. Acknowledgements ...............................................15 + +1. Introduction + +1.1. Purpose of This Document + + This document serves several purposes: + + 1. rationalize and generalize ABNF for some existing IMAP + extensions; + 2. collect the ABNF in one place in order to minimize cross + references between documents; + 3. define building blocks for future extensions so that they can + be used together in a compatible way. + + It is expected that a future revision of this document will be + incorporated into a revision of RFC 3501. + + This document updates ABNF in RFCs 2088, 2342, 3501, 3502, and 3516. + It also includes part of the errata to RFC 3501. This document + doesn't specify any semantic changes to the listed RFCs. + + The ABNF in section 6 of RFC 2342 got rewritten to conform to the + ABNF syntax as defined in RFC 4234 and to reference new non-terminals + from RFC 3501. It was also restructured to allow for better + readability. There were no changes "on the wire". + + Section 2 extends ABNF for SELECT, EXAMINE, CREATE, RENAME, FETCH/UID + FETCH, STORE/UID STORE, SEARCH, and APPEND commands in a consistent + manner. Extensions to all the commands but APPEND have the same + + + +Melnikov & Daboo Standards Track [Page 2] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + + structure. Extensibility for the APPEND command was done slightly + differently in order to preserve backward compatibility with existing + extensions. + + Section 2 also defines a new ESEARCH response, whose purpose is to + define a better version of the SEARCH response defined in RFC 3501. + + Section 3 defines the collected ABNF that replaces pieces of ABNF in + the aforementioned RFCs. The collected ABNF got generalized to allow + for easier future extensibility. + +1.2. Conventions Used in This Document + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. + + The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" + in this document are to be interpreted as defined in "Key words for + use in RFCs to Indicate Requirement Levels" [KEYWORDS]. + +2. IMAP ABNF Extensions + + This section is not normative. It provides some background on the + intended use of different extensions and it gives some guidance about + how future extensions should extend the described commands. + +2.1. Optional Parameters with the SELECT/EXAMINE Commands + + This document adds the ability to include one or more parameters with + the IMAP SELECT (section 6.3.1 of [IMAP4]) or EXAMINE (section 6.3.2 + of [IMAP4]) commands, to turn on or off certain standard behaviors, + or to add new optional behaviors required for a particular extension. + + There are two possible modes of operation: + + o A global state change where a single use of the optional parameter + will affect the session state from that time on, irrespective of + subsequent SELECT/EXAMINE commands. + + o A per-mailbox state change that will affect the session only for + the duration of the new selected state. A subsequent + SELECT/EXAMINE without the optional parameter will cancel its + effect for the newly selected mailbox. + + Optional parameters to the SELECT or EXAMINE commands are added as a + parenthesized list of attribute/value pairs, and appear after the + mailbox name in the standard SELECT or EXAMINE command. The order of + individual parameters is arbitrary. A parameter value is optional + + + +Melnikov & Daboo Standards Track [Page 3] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + + and may consist of atoms, strings, or lists in a specific order. If + the parameter value is present, it always appears in parentheses (*). + Any parameter not defined by extensions that the server supports must + be rejected with a BAD response. + + Example: + + C: a SELECT INBOX (ANNOTATE) + S: ... + S: a OK SELECT complete + + In the above example, a single parameter is used with the SELECT + command. + + Example: + + C: a EXAMINE INBOX (ANNOTATE RESPONSES ("UID Responses") + CONDSTORE) + S: ... + S: a OK EXAMINE complete + + In the above example, three parameters are used with the EXAMINE + command. The second parameter consists of two items: an atom + "RESPONSES" followed by a quoted string. + + Example: + + C: a SELECT INBOX (BLURDYBLOOP) + S: a BAD Unknown parameter in SELECT command + + In the above example, a parameter not supported by the server is + used. This results in the BAD response from the server. + + (*) - if a parameter has a mandatory value, which can always be + represented as a number or a sequence-set, the parameter value does + not need the enclosing (). See ABNF for more details. + +2.2. Extended CREATE Command + + Arguments: mailbox name + OPTIONAL list of CREATE parameters + + Responses: no specific responses for this command + + Result: OK - create completed + NO - create failure: cannot create mailbox with + that name + BAD - argument(s) invalid + + + +Melnikov & Daboo Standards Track [Page 4] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + + This document adds the ability to include one or more parameters with + the IMAP CREATE command (see section 6.3.3 of [IMAP4]), to turn on or + off certain standard behaviors, or to add new optional behaviors + required for a particular extension. No CREATE parameters are + defined in this document. + + Optional parameters to the CREATE command are added as a + parenthesized list of attribute/value pairs after the mailbox name. + The order of individual parameters is arbitrary. A parameter value + is optional and may consist of atoms, strings, or lists in a specific + order. If the parameter value is present, it always appears in + parentheses (*). Any parameter not defined by extensions that the + server supports must be rejected with a BAD response. + + (*) - if a parameter has a mandatory value, which can always be + represented as a number or a sequence-set, the parameter value does + not need the enclosing (). See ABNF for more details. + +2.3. Extended RENAME Command + + Arguments: existing mailbox name + new mailbox name + OPTIONAL list of RENAME parameters + + Responses: no specific responses for this command + + Result: OK - rename completed + NO - rename failure: cannot rename mailbox with + that name, cannot rename to mailbox with + that name, etc. + BAD - argument(s) invalid + + This document adds the ability to include one or more parameters with + the IMAP RENAME command (see section 6.3.5 of [IMAP4]), to turn on or + off certain standard behaviors, or to add new optional behaviors + required for a particular extension. No RENAME parameters are + defined in this document. + + Optional parameters to the RENAME command are added as a + parenthesized list of attribute/value pairs after the new mailbox + name. The order of individual parameters is arbitrary. A parameter + value is optional and may consist of atoms, strings, or lists in a + specific order. If the parameter value is present, it always appears + in parentheses (*). Any parameter not defined by extensions that the + server supports must be rejected with a BAD response. + + + + + + +Melnikov & Daboo Standards Track [Page 5] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + + (*) - if a parameter has a mandatory value, which can always be + represented as a number or a sequence-set, the parameter value does + not need the enclosing (). See ABNF for more details. + +2.4. Extensions to FETCH and UID FETCH Commands + + Arguments: sequence set + message data item names or macro + OPTIONAL fetch modifiers + + Responses: untagged responses: FETCH + + Result: OK - fetch completed + NO - fetch error: cannot fetch that data + BAD - command unknown or arguments invalid + + This document extends the syntax of the FETCH and UID FETCH commands + (see section 6.4.5 of [IMAP4]) to include optional FETCH modifiers. + No fetch modifiers are defined in this document. + + The order of individual modifiers is arbitrary. Each modifier is an + attribute/value pair. A modifier value is optional and may consist + of atoms and/or strings and/or lists in a specific order. If the + modifier value is present, it always appears in parentheses (*). Any + modifiers not defined by extensions that the server supports must be + rejected with a BAD response. + + (*) - if a modifier has a mandatory value, which can always be + represented as a number or a sequence-set, the modifier value does + not need the enclosing (). See ABNF for more details. + +2.5. Extensions to STORE and UID STORE Commands + + Arguments: message set + OPTIONAL store modifiers + message data item name + value for message data item + + Responses: untagged responses: FETCH + + Result: OK - store completed + NO - store error: cannot store that data + BAD - command unknown or arguments invalid + + This document extends the syntax of the STORE and UID STORE commands + (see section 6.4.6 of [IMAP4]) to include optional STORE modifiers. + No store modifiers are defined in this document. + + + + +Melnikov & Daboo Standards Track [Page 6] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + + The order of individual modifiers is arbitrary. Each modifier is an + attribute/value pair. A modifier value is optional and may consist + of atoms and/or strings and/or lists in a specific order. If the + modifier value is present, it always appears in parentheses (*). Any + modifiers not defined by extensions that the server supports must be + rejected with a BAD response. + + (*) - if a modifier has a mandatory value, which can always be + represented as a number or a sequence-set, the modifier value does + not need the enclosing (). See ABNF for more details. + +2.6. Extensions to SEARCH Command + +2.6.1. Extended SEARCH Command + + Arguments: OPTIONAL result specifier + OPTIONAL [CHARSET] specification + searching criteria (one or more) + + Responses: REQUIRED untagged response: SEARCH (*) + + Result: OK - search completed + NO - search error: cannot search that [CHARSET] or + criteria + BAD - command unknown or arguments invalid + + This section updates definition of the SEARCH command described in + section 6.4.4 of [IMAP4]. + + The SEARCH command is extended to allow for result options. This + document does not define any result options. + + The order of individual options is arbitrary. Individual options may + contain parameters enclosed in parentheses (**). If an option has + parameters, they consist of atoms and/or strings and/or lists in a + specific order. Any options not defined by extensions that the + server supports must be rejected with a BAD response. + + (*) - An extension to the SEARCH command may require another untagged + response, or no untagged response to be returned. Section 2.6.2 + defines a new ESEARCH untagged response that replaces the SEARCH + untagged response. Note that for a given extended SEARCH command the + SEARCH and ESEARCH responses SHOULD be mutually exclusive, i.e., only + one of them should be returned. + + (**) - if an option has a mandatory parameter, which can always be + represented as a number or a sequence-set, the option parameter does + not need the enclosing (). See ABNF for more details. + + + +Melnikov & Daboo Standards Track [Page 7] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + +2.6.2. ESEARCH untagged response + + Contents: one or more search-return-data pairs + + The ESEARCH response SHOULD be sent as a result of an extended SEARCH + or UID SEARCH command specified in section 2.6.1. + + The ESEARCH response starts with an optional search correlator. If + it is missing, then the response was not caused by a particular IMAP + command, whereas if it is present, it contains the tag of the command + that caused the response to be returned. + + The search correlator is followed by an optional UID indicator. If + this indicator is present, all data in the ESEARCH response refers to + UIDs, otherwise all returned data refers to message numbers. + + The rest of the ESEARCH response contains one or more search data + pairs. Each pair starts with unique return item name, followed by a + space and the corresponding data. Search data pairs may be returned + in any order. Unless specified otherwise by an extension, any return + item name SHOULD appear only once in an ESEARCH response. + + Example: S: * ESEARCH UID COUNT 5 ALL 4:19,21,28 + + Example: S: * ESEARCH (TAG "a567") UID COUNT 5 ALL 4:19,21,28 + + Example: S: * ESEARCH COUNT 5 ALL 1:17,21 + +2.7. Extensions to APPEND Command + + The IMAP BINARY extension [BINARY] extends the APPEND command to + allow a client to append data containing NULs by using the <literal8> + syntax. The ABNF was rewritten to allow for easier extensibility by + IMAP extensions. This document hasn't specified any semantical + changes to the [BINARY] extension. + + In addition, the non-terminal "literal8" defined in [BINARY] got + extended to allow for non-synchronizing literals if both [BINARY] and + [LITERAL+] extensions are supported by the server. + + The IMAP MULTIAPPEND extension [MULTIAPPEND] extends the APPEND + command to allow a client to append multiple messages atomically. + This document defines a common syntax for the APPEND command that + takes into consideration syntactic extensions defined by both + [BINARY] and [MULTIAPPEND] extensions. + + + + + + +Melnikov & Daboo Standards Track [Page 8] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + +3. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [ABNF]. + + Non-terminals referenced but not defined below are as defined by + [IMAP4]. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of uppercase or lowercase characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + append = "APPEND" SP mailbox 1*append-message + ;; only a single append-message may appear + ;; if MULTIAPPEND [MULTIAPPEND] capability + ;; is not present + + append-message = append-opts SP append-data + + append-ext = append-ext-name SP append-ext-value + ;; This non-terminal define extensions to + ;; to message metadata. + + append-ext-name = tagged-ext-label + + append-ext-value= tagged-ext-val + ;; This non-terminal shows recommended syntax + ;; for future extensions. + + + append-data = literal / literal8 / append-data-ext + + append-data-ext = tagged-ext + ;; This non-terminal shows recommended syntax + ;; for future extensions, + ;; i.e., a mandatory label followed + ;; by parameters. + + append-opts = [SP flag-list] [SP date-time] *(SP append-ext) + ;; message metadata + + charset = atom / quoted + ;; Exact syntax is defined in [CHARSET]. + + create = "CREATE" SP mailbox + [create-params] + ;; Use of INBOX gives a NO error. + + + +Melnikov & Daboo Standards Track [Page 9] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + + create-params = SP "(" create-param *( SP create-param) ")" + + create-param-name = tagged-ext-label + + create-param = create-param-name [SP create-param-value] + + create-param-value= tagged-ext-val + ;; This non-terminal shows recommended syntax + ;; for future extensions. + + + esearch-response = "ESEARCH" [search-correlator] [SP "UID"] + *(SP search-return-data) + ;; Note that SEARCH and ESEARCH responses + ;; SHOULD be mutually exclusive, + ;; i.e., only one of the response types + ;; should be + ;; returned as a result of a command. + + + examine = "EXAMINE" SP mailbox [select-params] + ;; modifies the original IMAP EXAMINE command + ;; to accept optional parameters + + fetch = "FETCH" SP sequence-set SP ("ALL" / "FULL" / + "FAST" / fetch-att / + "(" fetch-att *(SP fetch-att) ")") + [fetch-modifiers] + ;; modifies the original IMAP4 FETCH command to + ;; accept optional modifiers + + fetch-modifiers = SP "(" fetch-modifier *(SP fetch-modifier) ")" + + fetch-modifier = fetch-modifier-name [ SP fetch-modif-params ] + + fetch-modif-params = tagged-ext-val + ;; This non-terminal shows recommended syntax + ;; for future extensions. + + fetch-modifier-name = tagged-ext-label + + literal8 = "~{" number ["+"] "}" CRLF *OCTET + ;; A string that might contain NULs. + ;; <number> represents the number of OCTETs + ;; in the response string. + ;; The "+" is only allowed when both LITERAL+ and + ;; BINARY extensions are supported by the server. + + + + +Melnikov & Daboo Standards Track [Page 10] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + + mailbox-data =/ Namespace-Response / + esearch-response + + Namespace = nil / "(" 1*Namespace-Descr ")" + + Namespace-Command = "NAMESPACE" + + Namespace-Descr = "(" string SP + (DQUOTE QUOTED-CHAR DQUOTE / nil) + *(Namespace-Response-Extension) ")" + + Namespace-Response-Extension = SP string SP + "(" string *(SP string) ")" + + Namespace-Response = "NAMESPACE" SP Namespace + SP Namespace SP Namespace + ;; This response is currently only allowed + ;; if the IMAP server supports [NAMESPACE]. + ;; The first Namespace is the Personal Namespace(s) + ;; The second Namespace is the Other Users' Namespace(s) + ;; The third Namespace is the Shared Namespace(s) + + rename = "RENAME" SP mailbox SP mailbox + [rename-params] + ;; Use of INBOX as a destination gives + ;; a NO error, unless rename-params + ;; is not empty. + + rename-params = SP "(" rename-param *( SP rename-param) ")" + + rename-param = rename-param-name [SP rename-param-value] + + rename-param-name = tagged-ext-label + + rename-param-value= tagged-ext-val + ;; This non-terminal shows recommended syntax + ;; for future extensions. + + + response-data = "*" SP response-payload CRLF + + response-payload= resp-cond-state / resp-cond-bye / + mailbox-data / message-data / capability-data + + search = "SEARCH" [search-return-opts] + SP search-program + + search-correlator = SP "(" "TAG" SP tag-string ")" + + + +Melnikov & Daboo Standards Track [Page 11] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + + search-program = ["CHARSET" SP charset SP] + search-key *(SP search-key) + ;; CHARSET argument to SEARCH MUST be + ;; registered with IANA. + + search-return-data = search-modifier-name SP search-return-value + ;; Note that not every SEARCH return option + ;; is required to have the corresponding + ;; ESEARCH return data. + + search-return-opts = SP "RETURN" SP "(" [search-return-opt + *(SP search-return-opt)] ")" + + search-return-opt = search-modifier-name [SP search-mod-params] + + search-return-value = tagged-ext-val + ;; Data for the returned search option. + ;; A single "nz-number"/"number" value + ;; can be returned as an atom (i.e., without + ;; quoting). A sequence-set can be returned + ;; as an atom as well. + + search-modifier-name = tagged-ext-label + + search-mod-params = tagged-ext-val + ;; This non-terminal shows recommended syntax + ;; for future extensions. + + + select = "SELECT" SP mailbox [select-params] + ;; modifies the original IMAP SELECT command to + ;; accept optional parameters + + select-params = SP "(" select-param *(SP select-param) ")" + + select-param = select-param-name [SP select-param-value] + ;; a parameter to SELECT may contain one or + ;; more atoms and/or strings and/or lists. + + select-param-name= tagged-ext-label + + select-param-value= tagged-ext-val + ;; This non-terminal shows recommended syntax + ;; for future extensions. + + + status-att-list = status-att-val *(SP status-att-val) + ;; Redefines status-att-list from RFC 3501. + + + +Melnikov & Daboo Standards Track [Page 12] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + + ;; status-att-val is defined in RFC 3501 errata + + status-att-val = ("MESSAGES" SP number) / + ("RECENT" SP number) / + ("UIDNEXT" SP nz-number) / + ("UIDVALIDITY" SP nz-number) / + ("UNSEEN" SP number) + ;; Extensions to the STATUS responses + ;; should extend this production. + ;; Extensions should use the generic + ;; syntax defined by tagged-ext. + + store = "STORE" SP sequence-set [store-modifiers] + SP store-att-flags + ;; extend [IMAP4] STORE command syntax + ;; to allow for optional store-modifiers + + store-modifiers = SP "(" store-modifier *(SP store-modifier) + ")" + + store-modifier = store-modifier-name [SP store-modif-params] + + store-modif-params = tagged-ext-val + ;; This non-terminal shows recommended syntax + ;; for future extensions. + + store-modifier-name = tagged-ext-label + + tag-string = string + ;; tag of the command that caused + ;; the ESEARCH response, sent as + ;; a string. + + tagged-ext = tagged-ext-label SP tagged-ext-val + ;; recommended overarching syntax for + ;; extensions + + tagged-ext-label = tagged-label-fchar *tagged-label-char + ;; Is a valid RFC 3501 "atom". + + tagged-label-fchar = ALPHA / "-" / "_" / "." + + tagged-label-char = tagged-label-fchar / DIGIT / ":" + + + + + + + + +Melnikov & Daboo Standards Track [Page 13] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + + tagged-ext-comp = astring / + tagged-ext-comp *(SP tagged-ext-comp) / + "(" tagged-ext-comp ")" + ;; Extensions that follow this general + ;; syntax should use nstring instead of + ;; astring when appropriate in the context + ;; of the extension. + ;; Note that a message set or a "number" + ;; can always be represented as an "atom". + ;; An URL should be represented as + ;; a "quoted" string. + + tagged-ext-simple = sequence-set / number + + tagged-ext-val = tagged-ext-simple / + "(" [tagged-ext-comp] ")" + +4. Security Considerations + + This document updates ABNF in RFCs 2088, 2342, 3501, 3502, and 3516. + The updated documents must be consulted for security considerations + for the extensions that they define. + + As a protocol gets more complex, parser bugs become more common + including buffer overflow, denial of service, and other common + security coding errors. To the extent that this document makes the + parser more complex, it makes this situation worse. To the extent + that this document makes the parser more consistent and thus simpler, + the situation is improved. The impact will depend on how many + deployed IMAP extensions are consistent with this document. + Implementers are encouraged to take care of these issues when + extending existing implementations. Future IMAP extensions should + strive for consistency and simplicity to the greatest extent + possible. + + Extensions to IMAP commands that are permitted in NOT AUTHENTICATED + state are more sensitive to these security issues due to the larger + possible attacker community prior to authentication, and the fact + that some IMAP servers run with elevated privileges in that state. + This document does not extend any commands permitted in NOT + AUTHENTICATED state. Future IMAP extensions to commands permitted in + NOT AUTHENTICATED state should favor simplicity over consistency or + extensibility. + + + + + + + + +Melnikov & Daboo Standards Track [Page 14] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + +5. Normative References + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [IMAP4] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - + VERSION 4rev1", RFC 3501, March 2003. + + [ABNF] Crocker, D., Ed., and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", RFC 4234, October 2005. + + [CHARSET] Freed, N. and J. Postel, "IANA Charset Registration + Procedures", BCP 19, RFC 2978, October 2000. + + [MULTIAPPEND] Crispin, M., "Internet Message Access Protocol (IMAP) - + MULTIAPPEND Extension", RFC 3502, March 2003. + + [NAMESPACE] Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342, + May 1998. + + [LITERAL+] Myers, J., "IMAP4 non-synchronizing literals", RFC + 2088, January 1997. + + [BINARY] Nerenberg, L., "IMAP4 Binary Content Extension", RFC + 3516, April 2003. + +6. Acknowledgements + + This documents is based on ideas proposed by Pete Resnick, Mark + Crispin, Ken Murchison, Philip Guenther, Randall Gellens, and Lyndon + Nerenberg. + + However, all errors and omissions must be attributed to the authors + of the document. + + Thanks to Philip Guenther, Dave Cridland, Mark Crispin, Chris Newman, + Elwyn Davies, and Barry Leiba for comments and corrections. + + literal8 syntax was taken from RFC 3516. + + + + + + + + + + + + +Melnikov & Daboo Standards Track [Page 15] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + +Authors' Addresses + + Alexey Melnikov + Isode Limited + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex, TW12 2BX + UK + + EMail: Alexey.Melnikov@isode.com + + + Cyrus Daboo + + EMail: cyrus@daboo.name + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov & Daboo Standards Track [Page 16] + +RFC 4466 Collected Extensions to IMAP4 ABNF April 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + + + +Melnikov & Daboo Standards Track [Page 17] + diff --git a/imap/docs/rfc/rfc4467.txt b/imap/docs/rfc/rfc4467.txt new file mode 100644 index 00000000..83b6516a --- /dev/null +++ b/imap/docs/rfc/rfc4467.txt @@ -0,0 +1,1011 @@ + + + + + + +Network Working Group M. Crispin +Request for Comments: 4467 University of Washington +Updates: 3501 May 2006 +Category: Standards Track + + + Internet Message Access Protocol (IMAP) - URLAUTH Extension + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + This document describes the URLAUTH extension to the Internet Message + Access Protocol (IMAP) (RFC 3501) and the IMAP URL Scheme (IMAPURL) + (RFC 2192). This extension provides a means by which an IMAP client + can use URLs carrying authorization to access limited message data on + the IMAP server. + + An IMAP server that supports this extension indicates this with a + capability name of "URLAUTH". + +1. Introduction + + In [IMAPURL], a URL of the form imap://fred@example.com/INBOX/;uid=20 + requires authorization as userid "fred". However, [IMAPURL] implies + that it only supports authentication and confuses the concepts of + authentication and authorization. + + The URLAUTH extension defines an authorization mechanism for IMAP + URLs to replace [IMAPURL]'s authentication-only mechanism. URLAUTH + conveys authorization in the URL string itself and reuses a portion + of the syntax of the [IMAPURL] authentication mechanism to convey the + authorization identity (which also defines the default namespace in + [IMAP]). + + The URLAUTH extension provides a means by which an authorized user of + an IMAP server can create URLAUTH-authorized IMAP URLs. A URLAUTH- + authorized URL conveys authorization (not authentication) to the data + + + +Crispin Standards Track [Page 1] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + + addressed by that URL. This URL can be used in another IMAP session + to access specific content on the IMAP server, without otherwise + providing authorization to any other data (such as other data in the + mailbox specified in the URL) owned by the authorizing user. + + Conceptually, a URLAUTH-authorized URL can be thought of as a "pawn + ticket" that carries no authentication information and can be + redeemed by whomever presents it. However, unlike a pawn ticket, + URLAUTH has optional mechanisms to restrict the usage of a URLAUTH- + authorized URL. Using these mechanisms, URLAUTH-authorized URLs can + be usable by: + + . anonymous (the "pawn ticket" model) + . authenticated users only + . a specific authenticated user only + . message submission acting on behalf of a specific user only + + There is also a mechanism for expiration. + + A URLAUTH-authorized URL can be used in the argument to the BURL + command in message composition, as described in [BURL], for such + purposes as allowing a client (with limited memory or other + resources) to submit a message forward or to resend from an IMAP + mailbox without requiring the client to fetch that message data. + + The URLAUTH is generated using an authorization mechanism name and an + authorization token, which is generated using a secret mailbox access + key. An IMAP client can request that the server generate and assign + a new mailbox access key (thus effectively revoking all current URLs + using URLAUTH with the old mailbox access key) but cannot set the + mailbox access key to a key of its own choosing. + +1.1. Conventions Used in this Document + + The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" + in this document are to be interpreted as defined in [KEYWORDS]. + + The formal syntax uses the Augmented Backus-Naur Form (ABNF) notation + including the core rules defined in Appendix A of [ABNF]. + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. If a single "C:" or "S:" label applies to + multiple lines, then the line breaks between those lines are for + editorial clarity only and are not part of the actual protocol + exchange. + + + + + + +Crispin Standards Track [Page 2] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + +2. Concepts + +2.1. URLAUTH + + The URLAUTH is a component, appended at the end of a URL, that + conveys authorization to access the data addressed by that URL. It + contains an authorized access identifier, an authorization mechanism + name, and an authorization token. The authorization token is + generated from the URL, the authorized access identifier, the + authorization mechanism name, and a mailbox access key. + +2.2. Mailbox Access Key + + The mailbox access key is a random string with at least 128 bits of + entropy. It is generated by software (not by the human user) and + MUST be unpredictable. + + Each user has a table of mailboxes and an associated mailbox access + key for each mailbox. Consequently, the mailbox access key is per- + user and per-mailbox. In other words, two users sharing the same + mailbox each have a different mailbox access key for that mailbox, + and each mailbox accessed by a single user also has a different + mailbox access key. + +2.3. Authorized Access Identifier + + The authorized access identifier restricts use of the URLAUTH + authorized URL to certain users authorized on the server, as + described in section 3. + +2.4. Authorization Mechanism + + The authorization mechanism is the algorithm by which the URLAUTH is + generated and subsequently verified, using the mailbox access key. + +2.4.1. INTERNAL Authorization Mechanism + + This specification defines the INTERNAL mechanism, which uses a token + generation algorithm of the server's choosing and does not involve + disclosure of the mailbox access key to the client. + + Note: The token generation algorithm chosen by the server + implementation should be modern and reasonably secure. At the + time of the writing of this document, an [HMAC] such as HMAC-SHA1 + is recommended. + + + + + + +Crispin Standards Track [Page 3] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + + If it becomes necessary to change the token generation algorithm + of the INTERNAL mechanism (e.g., because an attack against the + current algorithm has been discovered), all currently existing + URLAUTH-authorized URLs are invalidated by the change in + algorithm. Since this would be an unpleasant surprise to + applications that depend upon the validity of a URLAUTH-authorized + URL, and there is no good way to do a bulk update of existing + deployed URLs, it is best to avoid this situation by using a + secure algorithm as opposed to one that is "good enough". + + Server implementations SHOULD consider the possibility of changing + the algorithm. In some cases, it may be desirable to implement + the change of algorithm in a way that newly-generated tokens use + the new algorithm, but that for a limited period of time tokens + using either the new or old algorithm can be validated. + Consequently, the server SHOULD incorporate some means of + identifying the token generation algorithm within the token. + + Although this specification is extensible for other mechanisms, none + are defined in this document. In addition to the mechanism name + itself, other mechanisms may have mechanism-specific data, which is + to be interpreted according to the definition of that mechanism. + +2.5. Authorization Token + + The authorization token is a deterministic string of at least 128 + bits that an entity with knowledge of the secret mailbox access key + and URL authorization mechanism can use to verify the URL. + +3. IMAP URL Extensions + + [IMAPURL] is extended by allowing the addition of + ";EXPIRE=<datetime>" and ";URLAUTH=<access>:<mech>:<token>" to IMAP + URLs that refer to a specific message or message parts. + + The URLAUTH is comprised of ";URLAUTH=<access>:<mech>:<token>" and + MUST be at the end of the URL. + + URLAUTH does not apply to, and MUST NOT be used with, any IMAP URL + that refers to an entire IMAP server, a list of mailboxes, an entire + IMAP mailbox, or IMAP search results. + + When ";EXPIRE=<datetime>" is used, this indicates the latest date and + time that the URL is valid. After that date and time, the URL has + expired, and server implementations MUST reject the URL. If + ";EXPIRE=<datetime>" is not used, the URL has no expiration, but + still can be revoked as discussed below. + + + + +Crispin Standards Track [Page 4] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + + The URLAUTH takes the form ";URLAUTH=<access>:<mech>:<token>". It is + composed of three parts. The <access> portion provides the + authorized access identifiers, which may constrain the operations and + users that are permitted to use this URL. The <mech> portion + provides the authorization mechanism used by the IMAP server to + generate the authorization token that follows. The <token> portion + provides the authorization token. + + The "submit+" access identifier prefix, followed by a userid, + indicates that only a userid authorized as a message submission + entity on behalf of the specified userid is permitted to use this + URL. The IMAP server does not validate the specified userid but does + validate that the IMAP session has an authorization identity that is + authorized as a message submission entity. The authorized message + submission entity MUST validate the userid prior to contacting the + IMAP server. + + The "user+" access identifier prefix, followed by a userid, indicates + that use of this URL is limited to IMAP sessions that are logged in + as the specified userid (that is, have authorization identity as that + userid). + + Note: If a SASL mechanism that provides both authorization and + authentication identifiers is used to authenticate to the IMAP + server, the "user+" access identifier MUST match the authorization + identifier. + + The "authuser" access identifier indicates that use of this URL is + limited to IMAP sessions that are logged in as an authorized user + (that is, have authorization identity as an authorized user) of that + IMAP server. Use of this URL is prohibited to anonymous IMAP + sessions. + + The "anonymous" access identifier indicates that use of this URL is + not restricted by session authorization identity; that is, any IMAP + session in authenticated or selected state (as defined in [IMAP]), + including anonymous sessions, may issue a URLFETCH using this URL. + + The authorization token is represented as an ASCII-encoded + hexadecimal string, which is used to authorize the URL. The length + and the calculation of the authorization token depends upon the + mechanism used; but, in all cases, the authorization token is at + least 128 bits (and therefore at least 32 hexadecimal digits). + + + + + + + + +Crispin Standards Track [Page 5] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + +4. Discussion of URLAUTH Authorization Issues + + In [IMAPURL], the userid before the "@" in the URL has two purposes: + + 1) It provides context for user-specific mailbox paths such as + "INBOX". + + 2) It specifies that resolution of the URL requires logging in as + that user and limits use of that URL to only that user. + + An obvious limitation of using the same field for both purposes is + that the URL can only be resolved by the mailbox owner. + + URLAUTH overrides the second purpose of the userid in the IMAP URL + and by default permits the URL to be resolved by any user permitted + by the access identifier. + + The "user+<userid>" access identifier limits resolution of that URL + to a particular userid, whereas the "submit+<userid>" access + identifier is more general and simply requires that the session be + authorized by a user that has been granted a "submit" role within the + authentication system. Use of either of these access identifiers + makes it impossible for an attacker, spying on the session, to use + the same URL, either directly or by submission to a message + submission entity. + + The "authuser" and "anonymous" access identifiers do not have this + level of protection and should be used with caution. These access + identifiers are primarily useful for public export of data from an + IMAP server, without requiring that it be copied to a web or + anonymous FTP server. Refer to the Security Considerations for more + details. + +5. Generation of URLAUTH-Authorized URLs + + A URLAUTH-authorized URL is generated from an initial URL as follows: + + An initial URL is built, ending with ";URLAUTH=<access>" but without + the ":<mech>:<token>" components. An authorization mechanism is + selected and used to calculate the authorization token, with the + initial URL as the data and a secret known to the IMAP server as the + key. The URLAUTH-authorized URL is generated by taking the initial + URL and appending ":", the URL authorization mechanism name, ":", and + the ASCII-encoded hexadecimal representation of the authorization + token. + + + + + + +Crispin Standards Track [Page 6] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + + Note: ASCII-encoded hexadecimal is used instead of BASE64 because + a BASE64 representation may have "=" padding characters, which + would be problematic in a URL. + + In the INTERNAL mechanism, the mailbox access key for that mailbox is + the secret known to the IMAP server, and a server-selected algorithm + is used as described in section 2.4.1. + +6. Validation of URLAUTH-authorized URLs + + A URLAUTH-authorized URL is validated as follows: + + The URL is split at the ":" that separates "<access>" from + "<mech>:<token>" in the ";URLAUTH=<access>:<mech>:<token>" portion of + the URL. The "<mech>:<token>" portion is first parsed and saved as + the authorization mechanism and the authorization token. The URL is + truncated, discarding the ":" described above, to create a "rump URL" + (the URL minus the ":" and the "<mech>:<token>" portion). The rump + URL is then analyzed to identify the mailbox. + + If the mailbox cannot be identified, an authorization token is + calculated on the rump URL, using random "plausible" keys (selected + by the server) as needed, before returning a validation failure. + This prevents timing attacks aimed at identifying mailbox names. + + If the mailbox can be identified, the authorization token is + calculated on the rump URL and a secret known to the IMAP server + using the given URL authorization mechanism. Validation is + successful if, and only if, the calculated authorization token for + that mechanism matches the authorization token supplied in + ";URLAUTH=<access>:<mech>:<token>". + + Removal of the ":<mech>:<token>" portion of the URL MUST be the only + operation applied to the URLAUTH-authorized URL to get the rump URL. + In particular, URL percent escape decoding and case-folding + (including to the domain part of the URL) MUST NOT occur. + + In the INTERNAL mechanism, the mailbox access key for that mailbox is + used as the secret known to the IMAP server, and the same server- + selected algorithm used for generating URLs is used to calculate the + authorization token for verification. + + + + + + + + + + +Crispin Standards Track [Page 7] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + +7. Additional Commands + + These commands are extensions to the [IMAP] base protocol. + + The section headings of these commands are intended to correspond + with where they would be located in the base protocol document if + they were part of that document. + +BASE.6.3.RESETKEY. RESETKEY Command + + Arguments: optional mailbox name + optional mechanism name(s) + + Responses: none other than in result + + Result: OK - RESETKEY completed, URLMECH containing new data + NO - RESETKEY error: can't change key of that mailbox + BAD - command unknown or arguments invalid + + The RESETKEY command has two forms. + + The first form accepts a mailbox name as an argument and generates a + new mailbox access key for the given mailbox in the user's mailbox + access key table, replacing any previous mailbox access key (and + revoking any URLs that were authorized with a URLAUTH using that key) + in that table. By default, the mailbox access key is generated for + the INTERNAL mechanism; other mechanisms can be specified with the + optional mechanism argument. + + The second form, with no arguments, removes all mailbox access keys + in the user's mailbox access key table, revoking all URLs currently + authorized using URLAUTH by the user. + + Any current IMAP session logged in as the user that has the mailbox + selected will receive an untagged OK response with the URLMECH status + response code (see section BASE.7.1.URLMECH for more details about + the URLMECH status response code). + + Example: + + C: a31 RESETKEY + S: a31 OK All keys removed + C: a32 RESETKEY INBOX + S: a32 OK [URLMECH INTERNAL] mechs + C: a33 RESETKEY INBOX XSAMPLE + S: a33 OK [URLMECH INTERNAL XSAMPLE=P34OKhO7VEkCbsiYY8rGEg==] done + + + + + +Crispin Standards Track [Page 8] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + +BASE.6.3.GENURLAUTH. GENURLAUTH Command + + Argument: one or more URL/mechanism pairs + + Response: untagged response: GENURLAUTH + + Result: OK - GENURLAUTH completed + NO - GENURLAUTH error: can't generate a URLAUTH + BAD - command unknown or arguments invalid + + The GENURLAUTH command requests that the server generate a URLAUTH- + authorized URL for each of the given URLs using the given URL + authorization mechanism. + + The server MUST validate each supplied URL as follows: + + (1) The mailbox component of the URL MUST refer to an existing + mailbox. + + (2) The server component of the URL MUST contain a valid userid + that identifies the owner of the mailbox access key table that + will be used to generate the URLAUTH-authorized URL. As a + consequence, the iserver rule of [IMAPURL] is modified so that + iuserauth is mandatory. + + Note: the server component of the URL is generally the + logged in userid and server. If not, then the logged in + userid and server MUST have owner-type access to the + mailbox access key table owned by the userid and server + indicated by the server component of the URL. + + (3) There is a valid access identifier that, in the case of + "submit+" and "user+", will contain a valid userid. This + userid is not necessarily the same as the owner userid + described in (2). + + (4) The server MAY also verify that the iuid and/or isection + components (if present) are valid. + + If any of the above checks fail, the server MUST return a tagged BAD + response with the following exception. If an invalid userid is + supplied as the mailbox access key owner and/or as part of the access + identifier, the server MAY issue a tagged OK response with a + generated mailbox key that always fails validation when used with a + URLFETCH command. This exception prevents an attacker from + validating userids. + + + + + +Crispin Standards Track [Page 9] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + + If there is currently no mailbox access key for the given mailbox in + the owner's mailbox access key table, one is automatically generated. + That is, it is not necessary to use RESETKEY prior to first-time use + of GENURLAUTH. + + If the command is successful, a GENURLAUTH response code is returned + listing the requested URLs as URLAUTH-authorized URLs. + + Examples: + + C: a775 GENURLAUTH "imap://joe@example.com/INBOX/;uid=20/ + ;section=1.2" INTERNAL + S: a775 BAD missing access identifier in supplied URL + C: a776 GENURLAUTH "imap://example.com/Shared/;uid=20/ + ;section=1.2;urlauth=submit+fred" INTERNAL + S: a776 BAD missing owner username in supplied URL + C: a777 GENURLAUTH "imap://joe@example.com/INBOX/;uid=20/ + ;section=1.2;urlauth=submit+fred" INTERNAL + S: * GENURLAUTH "imap://joe@example.com/INBOX/;uid=20/;section=1.2 + ;urlauth=submit+fred:internal:91354a473744909de610943775f92038" + S: a777 OK GENURLAUTH completed + +BASE.6.3.URLFETCH. URLFETCH Command + + Argument: one or more URLs + + Response: untagged response: URLFETCH + + Result: OK - urlfetch completed + NO - urlfetch failed due to server internal error + BAD - command unknown or arguments invalid + + The URLFETCH command requests that the server return the text data + associated with the specified IMAP URLs, as described in [IMAPURL] + and extended by this document. The data is returned for all + validated URLs, regardless of whether or not the session would + otherwise be able to access the mailbox containing that data via + SELECT or EXAMINE. + + Note: This command does not require that the URL refer to the + selected mailbox; nor does it require that any mailbox be + selected. It also does not in any way interfere with any selected + mailbox. + + + + + + + + +Crispin Standards Track [Page 10] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + + The URLFETCH command effectively executes with the access of the + userid in the server component of the URL (which is generally the + userid that issued the GENURLAUTH). By itself, the URLAUTH does NOT + grant access to the data; once validated, it grants whatever access + to the data is held by the userid in the server component of the URL. + That access may have changed since the GENURLAUTH was done. + + The URLFETCH command MUST return an untagged URLFETCH response and a + tagged OK response to any URLFETCH command that is syntactically + valid. A NO response indicates a server internal failure that may be + resolved on later retry. + + Note: The possibility of a NO response is to accommodate + implementations that would otherwise have to issue an untagged BYE + with a fatal error due to an inability to respond to a valid + request. In an ideal world, a server SHOULD NOT issue a NO + response. + + The server MUST return NIL for any IMAP URL that references an entire + IMAP server, a list of mailboxes, an entire IMAP mailbox, or IMAP + search results. + + Example: + + Note: For clarity, this example uses the LOGIN command, which + SHOULD NOT be used over a non-encrypted communication path. + + This example is of a submit server, obtaining a message segment + for a message that it has already validated was submitted by + "fred". + + S: * OK [CAPABILITY IMAP4REV1 URLAUTH] example.com IMAP server + C: a001 LOGIN submitserver secret + S: a001 OK submitserver logged in + C: a002 URLFETCH "imap://joe@example.com/INBOX/;uid=20/ + ;section=1.2;urlauth=submit+fred:internal + :91354a473744909de610943775f92038" + S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/;section=1.2 + ;urlauth=submit+fred:internal + :91354a473744909de610943775f92038" {28} + S: Si vis pacem, para bellum. + S: + S: a002 OK URLFETCH completed + + + + + + + + +Crispin Standards Track [Page 11] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + +8. Additional Responses + + These responses are extensions to the [IMAP] base protocol. + + The section headings of these responses are intended to correspond + with where they would be located in the base protocol document if + they were part of that document. + +BASE.7.1.URLMECH. URLMECH Status Response Code + + The URLMECH status response code is followed by a list of URL + authorization mechanism names. Mechanism names other than INTERNAL + may be appended with an "=" and BASE64-encoded form of mechanism- + specific data. + + This status response code is returned in an untagged OK response in + response to a RESETKEY, SELECT, or EXAMINE command. In the case of + the RESETKEY command, this status response code can be sent in the + tagged OK response instead of requiring a separate untagged OK + response. + + Example: + + C: a33 RESETKEY INBOX XSAMPLE + S: a33 OK [URLMECH INTERNAL XSAMPLE=P34OKhO7VEkCbsiYY8rGEg==] done + + In this example, the server supports the INTERNAL mechanism and an + experimental mechanism called XSAMPLE, which also holds some + mechanism-specific data (the name "XSAMPLE" is for illustrative + purposes only). + +BASE.7.4.GENURLAUTH. GENURLAUTH Response + + Contents: One or more URLs + + The GENURLAUTH response returns the URLAUTH-authorized URL(s) + requested by a GENURLAUTH command. + + Example: + + C: a777 GENURLAUTH "imap://joe@example.com/INBOX/;uid=20/ + ;section=1.2;urlauth=submit+fred" INTERNAL + S: * GENURLAUTH "imap://joe@example.com/INBOX/;uid=20/;section=1.2 + ;urlauth=submit+fred:internal:91354a473744909de610943775f92038" + S: a777 OK GENURLAUTH completed + + + + + + +Crispin Standards Track [Page 12] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + +BASE.7.4.URLFETCH. URLFETCH Response + + Contents: One or more URL/nstring pairs + + The URLFETCH response returns the message text data associated with + one or more IMAP URLs, as described in [IMAPURL] and extended by this + document. This response occurs as the result of a URLFETCH command. + + The returned data string is NIL if the URL is invalid for any reason + (including validation failure). If the URL is valid, but the IMAP + fetch of the body part returned NIL (this should not happen), the + returned data string should be the empty string ("") and not NIL. + + Note: This command does not require that the URL refer to the + selected mailbox; nor does it require that any mailbox be + selected. It also does not in any way interfere with any selected + mailbox. + + Example: + + C: a002 URLFETCH "imap://joe@example.com/INBOX/;uid=20/ + ;section=1.2;urlauth=submit+fred:internal + :91354a473744909de610943775f92038" + S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/;section=1.2 + ;urlauth=submit+fred:internal + :91354a473744909de610943775f92038" {28} + S: Si vis pacem, para bellum. + S: + S: a002 OK URLFETCH completed + +9. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [ABNF]. + + The following modifications are made to the Formal Syntax in [IMAP]: + +resetkey = "RESETKEY" [SP mailbox *(SP mechanism)] + +capability =/ "URLAUTH" + +command-auth =/ resetkey / genurlauth / urlfetch + +resp-text-code =/ "URLMECH" SP "INTERNAL" *(SP mechanism ["=" base64]) + +genurlauth = "GENURLAUTH" 1*(SP url-rump SP mechanism) + +genurlauth-data = "*" SP "GENURLAUTH" 1*(SP url-full) + + + +Crispin Standards Track [Page 13] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + +url-full = astring + ; contains authimapurlfull as defined below + +url-rump = astring + ; contains authimapurlrump as defined below + +urlfetch = "URLFETCH" 1*(SP url-full) + +urlfetch-data = "*" SP "URLFETCH" 1*(SP url-full SP nstring) + + The following extensions are made to the Formal Syntax in [IMAPURL]: + +authimapurl = "imap://" enc-user [iauth] "@" hostport "/" + imessagepart + ; replaces "imapurl" and "iserver" rules for + ; URLAUTH authorized URLs + +authimapurlfull = authimapurl iurlauth + +authimapurlrump = authimapurl iurlauth-rump + +enc-urlauth = 32*HEXDIG + +enc-user = 1*achar + ; same as "enc_user" in RFC 2192 + +iurlauth = iurlauth-rump ":" mechanism ":" enc-urlauth + +iurlauth-rump = [expire] ";URLAUTH=" access + +access = ("submit+" enc-user) / ("user+" enc-user) / + "authuser" / "anonymous" + +expire = ";EXPIRE=" date-time + ; date-time defined in [DATETIME] + +mechanism = "INTERNAL" / 1*(ALPHA / DIGIT / "-" / ".") + ; case-insensitive + ; new mechanisms MUST be registered with IANA + + + + + + + + + + + + +Crispin Standards Track [Page 14] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + +10. Security Considerations + + Security considerations are discussed throughout this memo. + + The mailbox access key SHOULD have at least 128 bits of entropy + (refer to [RANDOM] for more details) and MUST be unpredictable. + + The server implementation of the INTERNAL mechanism SHOULD consider + the possibility of needing to change the token generation algorithm, + and SHOULD incorporate some means of identifying the token generation + algorithm within the token. + + The URLMECH status response code may expose sensitive data in the + mechanism-specific data for mechanisms other than INTERNAL. A server + implementation MUST implement a configuration that will not return a + URLMECH status response code unless some mechanism is provided that + protects the session from snooping, such as a TLS or SASL security + layer that provides confidentiality protection. + + The calculation of an authorization token with a "plausible" key if + the mailbox can not be identified is necessary to avoid attacks in + which the server is probed to see if a particular mailbox exists on + the server by measuring the amount of time taken to reject a known + bad name versus some other name. + + To protect against a computational denial-of-service attack, a server + MAY impose progressively longer delays on multiple URL requests that + fail validation. + + The decision to use the "authuser" access identifier should be made + with caution. An "authuser" access identifier can be used by any + authorized user of the IMAP server; therefore, use of this access + identifier should be limited to content that may be disclosed to any + authorized user of the IMAP server. + + The decision to use the "anonymous" access identifier should be made + with extreme caution. An "anonymous" access identifier can be used + by anyone; therefore, use of this access identifier should be limited + to content that may be disclosed to anyone. Many IMAP servers do not + permit anonymous access; in this case, the "anonymous" access + identifier is equivalent to "authuser", but this MUST NOT be relied + upon. + + Although this specification does not prohibit the theoretical + capability to generate a URL with a server component other than the + logged in userid and server, this capability should only be provided + + + + + +Crispin Standards Track [Page 15] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + + when the logged in userid/server has been authorized as equivalent to + the server component userid/server, or otherwise has access to that + userid/server mailbox access key table. + +11. IANA Considerations + + This document constitutes registration of the URLAUTH capability in + the imap4-capabilities registry. + + URLAUTH authorization mechanisms are registered by publishing a + standards track or IESG-approved experimental RFC. The registry is + currently located at: + +http://www.iana.org/assignments/urlauth-authorization-mechanism-registry + + This registry is case-insensitive. + + This document constitutes registration of the INTERNAL URLAUTH + authorization mechanism. + + IMAP URLAUTH Authorization Mechanism Registry + + Mechanism Name Reference + -------------- --------- + INTERNAL [RFC4467] + + + + + + + + + + + + + + + + + + + + + + + + + + +Crispin Standards Track [Page 16] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + +12. Normative References + + [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 4234, October 2005. + + [BURL] Newman, C., "Message Submission BURL Extension", RFC 4468, + May 2006. + + [DATETIME] Klyne, G. and C. Newman, "Date and Time on the Internet: + Timestamps", RFC 3339, July 2002. + + [IMAP] Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 3501, March 2003. + + [IMAPURL] Newman, C., "IMAP URL Scheme", RFC 2192, September 1997. + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + +13. Informative References + + [HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- + Hashing for Message Authentication", RFC 2104, February + 1997. + + [RANDOM] Eastlake, D., 3rd, Schiller, J., and S. Crocker, + "Randomness Requirements for Security", BCP 106, RFC 4086, + June 2005. + +Author's Address + + Mark R. Crispin + Networks and Distributed Computing + University of Washington + 4545 15th Avenue NE + Seattle, WA 98105-4527 + + Phone: (206) 543-5762 + EMail: MRC@CAC.Washington.EDU + + + + + + + + + + + + +Crispin Standards Track [Page 17] + +RFC 4467 IMAP - URLAUTH Extension May 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + + + +Crispin Standards Track [Page 18] + diff --git a/imap/docs/rfc/rfc4468.txt b/imap/docs/rfc/rfc4468.txt new file mode 100644 index 00000000..b16dcb4e --- /dev/null +++ b/imap/docs/rfc/rfc4468.txt @@ -0,0 +1,787 @@ + + + + + + +Network Working Group C. Newman +Request for Comments: 4468 Sun Microsystems +Updates: 3463 May 2006 +Category: Standards Track + + + Message Submission BURL Extension + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + The submission profile of Simple Mail Transfer Protocol (SMTP) + provides a standard way for an email client to submit a complete + message for delivery. This specification extends the submission + profile by adding a new BURL command that can be used to fetch + submission data from an Internet Message Access Protocol (IMAP) + server. This permits a mail client to inject content from an IMAP + server into the SMTP infrastructure without downloading it to the + client and uploading it back to the server. + + + + + + + + + + + + + + + + + + + + + +Newman Standards Track [Page 1] + +RFC 4468 Message Submission BURL Extension May 2006 + + +Table of Contents + + 1. Introduction ....................................................2 + 2. Conventions Used in This Document ...............................2 + 3. BURL Submission Extension .......................................3 + 3.1. SMTP Submission Extension Registration .....................3 + 3.2. BURL Transaction ...........................................3 + 3.3. The BURL IMAP Options ......................................4 + 3.4. Examples ...................................................5 + 3.5. Formal Syntax ..............................................6 + 4. 8-Bit and Binary ................................................7 + 5. Updates to RFC 3463 .............................................7 + 6. Response Codes ..................................................7 + 7. IANA Considerations .............................................9 + 8. Security Considerations .........................................9 + 9. References .....................................................11 + 9.1. Normative References ......................................11 + 9.2. Informative References ....................................12 + Appendix A. Acknowledgements .....................................13 + +1. Introduction + + This specification defines an extension to the standard Message + Submission [RFC4409] protocol to permit data to be fetched from an + IMAP server at message submission time. This MAY be used in + conjunction with the CHUNKING [RFC3030] mechanism so that chunks of + the message can come from an external IMAP server. This provides the + ability to forward an email message without first downloading it to + the client. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" + in this document are to be interpreted as defined in "Key words for + use in RFCs to Indicate Requirement Levels" [RFC2119]. + + The formal syntax uses the Augmented Backus-Naur Form (ABNF) + [RFC4234] notation including the core rules defined in Appendix B of + RFC 4234. + + + + + + + + + + + + +Newman Standards Track [Page 2] + +RFC 4468 Message Submission BURL Extension May 2006 + + +3. BURL Submission Extension + + This section defines the BURL submission extension. + +3.1. SMTP Submission Extension Registration + + 1. The name of this submission extension is "BURL". This extends + the Message Submission protocol on port 587 and MUST NOT be + advertised by a regular SMTP [RFC2821] server on port 25 that + acts as a relay for incoming mail from other SMTP relays. + + 2. The EHLO keyword value associated with the extension is "BURL". + + 3. The BURL EHLO keyword will have zero or more arguments. The only + argument defined at this time is the "imap" argument, which MUST + be present in order to use IMAP URLs with BURL. Clients MUST + ignore other arguments after the BURL EHLO keyword unless they + are defined by a subsequent IETF standards track specification. + The arguments that appear after the BURL EHLO keyword may change + subsequent to the use of SMTP AUTH [RFC2554], so a server that + advertises BURL with no arguments prior to authentication + indicates that BURL is supported but authentication is required + to use it. + + 4. This extension adds the BURL SMTP verb. This verb is used as a + replacement for the DATA command and is only permitted during a + mail transaction after at least one successful RCPT TO. + +3.2. BURL Transaction + + A simple BURL transaction will consist of MAIL FROM, one or more RCPT + TO headers, and a BURL command with the "LAST" tag. The BURL command + will include an IMAP URL pointing to a fully formed message ready for + injection into the SMTP infrastructure. If PIPELINING [RFC2920] is + advertised, the client MAY send the entire transaction in one round + trip. If no valid RCPT TO address is supplied, the BURL command will + simply fail, and no resolution of the BURL URL argument will be + performed. If at least one valid RCPT TO address is supplied, then + the BURL URL argument will be resolved before the server responds to + the command. + + A more sophisticated BURL transaction MAY occur when the server also + advertises CHUNKING [RFC3030]. In this case, the BURL and BDAT + commands may be interleaved until one of them terminates the + transaction with the "LAST" argument. If PIPELINING [RFC2920] is + also advertised, then the client may pipeline the entire transaction + in one round-trip. However, it MUST wait for the results of the + "LAST" BDAT or BURL command prior to initiating a new transaction. + + + +Newman Standards Track [Page 3] + +RFC 4468 Message Submission BURL Extension May 2006 + + + The BURL command directs the server to fetch the data object to which + the URL refers and include it in the message. If the URL fetch + fails, the server will fail the entire transaction. + +3.3. The BURL IMAP Options + + When "imap" is present in the space-separated list of arguments + following the BURL EHLO keyword, it indicates that the BURL command + supports the URLAUTH [RFC4467] extended form of IMAP URLs [RFC2192] + and that the submit server is configured with the necessary + credentials to resolve "urlauth=submit+" IMAP URLs for the submit + server's domain. + + Subsequent to a successful SMTP AUTH command, the submission server + MAY indicate a prearranged trust relationship with a specific IMAP + server by including a BURL EHLO keyword argument of the form + "imap://imap.example.com". In this case, the submission server will + permit a regular IMAP URL referring to messages or parts of messages + on imap.example.com that the user who authenticated to the submit + server can access. Note that this form does not imply that the + submit server supports URLAUTH URLs; the submit server must advertise + both "imap" and "imap://imap.example.com" to indicate support for + both extended and non-extended URL forms. + + When the submit server connects to the IMAP server, it acts as an + IMAP client and thus is subject to both the mandatory-to-implement + IMAP capabilities in Section 6.1.1 of RFC 3501, and the security + considerations in Section 11 of RFC 3501. Specifically, this + requires that the submit server implement a configuration that uses + STARTTLS followed by SASL PLAIN [SASL-PLAIN] to authenticate to the + IMAP server. + + When the submit server resolves a URLAUTH IMAP URL, it uses submit + server credentials when authenticating to the IMAP server. The + authentication identity and password used for submit credentials MUST + be configurable. The string "submit" is suggested as a default value + for the authentication identity, with no default for the password. + Typically, the authorization identity is empty in this case; thus the + IMAP server will derive the authorization identity from the + authentication identity. If the IMAP URL uses the "submit+" access + identifier prefix, the submit server MUST refuse the BURL command + unless the userid in the URL's <access> token matches the submit + client's authorization identity. + + When the submit server resolves a regular IMAP URL, it uses the + submit client's authorization identity when authenticating to the + IMAP server. If both the submit client and the submit server's + embedded IMAP client use SASL PLAIN (or the equivalent), the submit + + + +Newman Standards Track [Page 4] + +RFC 4468 Message Submission BURL Extension May 2006 + + + server SHOULD forward the client's credentials if and only if the + submit server knows that the IMAP server is in the same + administrative domain. If the submit server supports SASL mechanisms + other than PLAIN, it MUST implement a configuration in which the + submit server's embedded IMAP client uses STARTTLS and SASL PLAIN + with the submit server's authentication identity and password (for + the respective IMAP server) and the submit client's authorization + identity. + +3.4. Examples + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. If a single "C:" or "S:" label applies to + multiple lines, then the line breaks between those lines are for + editorial clarity only and are not part of the actual protocol + exchange. + + Two successful submissions (without and with pipelining) follow: + + <SSL/TLS encryption layer negotiated> + C: EHLO potter.example.com + S: 250-owlry.example.com + S: 250-8BITMIME + S: 250-BURL imap + S: 250-AUTH PLAIN + S: 250-DSN + S: 250 ENHANCEDSTATUSCODES + C: AUTH PLAIN aGFycnkAaGFycnkAYWNjaW8= + S: 235 2.7.0 PLAIN authentication successful. + C: MAIL FROM:<harry@gryffindor.example.com> + S: 250 2.5.0 Address Ok. + C: RCPT TO:<ron@gryffindor.example.com> + S: 250 2.1.5 ron@gryffindor.example.com OK. + C: BURL imap://harry@gryffindor.example.com/outbox + ;uidvalidity=1078863300/;uid=25;urlauth=submit+harry + :internal:91354a473744909de610943775f92038 LAST + S: 250 2.5.0 Ok. + + <SSL/TLS encryption layer negotiated> + C: EHLO potter.example.com + S: 250-owlry.example.com + S: 250-8BITMIME + S: 250-PIPELINING + S: 250-BURL imap + S: 250-AUTH PLAIN + S: 250-DSN + S: 250 ENHANCEDSTATUSCODES + C: AUTH PLAIN aGFycnkAaGFycnkAYWNjaW8= + + + +Newman Standards Track [Page 5] + +RFC 4468 Message Submission BURL Extension May 2006 + + + C: MAIL FROM:<harry@gryffindor.example.com> + C: RCPT TO:<ron@gryffindor.example.com> + C: BURL imap://harry@gryffindor.example.com/outbox + ;uidvalidity=1078863300/;uid=25;urlauth=submit+harry + :internal:91354a473744909de610943775f92038 LAST + S: 235 2.7.0 PLAIN authentication successful. + S: 250 2.5.0 Address Ok. + S: 250 2.1.5 ron@gryffindor.example.com OK. + S: 250 2.5.0 Ok. + + Note that PIPELINING of the AUTH command is only permitted if the + selected mechanism can be completed in one round trip, a client + initial response is provided, and no SASL security layer is + negotiated. This is possible for PLAIN and EXTERNAL, but not for + most other SASL mechanisms. + + Some examples of failure cases: + + C: MAIL FROM:<harry@gryffindor.example.com> + C: RCPT TO:<malfoy@slitherin.example.com> + C: BURL imap://harry@gryffindor.example.com/outbox + ;uidvalidity=1078863300/;uid=25;urlauth=submit+harry + :internal:91354a473744909de610943775f92038 LAST + S: 250 2.5.0 Address Ok. + S: 550 5.7.1 Relaying not allowed: malfoy@slitherin.example.com + S: 554 5.5.0 No recipients have been specified. + + C: MAIL FROM:<harry@gryffindor.example.com> + C: RCPT TO:<ron@gryffindor.example.com> + C: BURL imap://harry@gryffindor.example.com/outbox + ;uidvalidity=1078863300/;uid=25;urlauth=submit+harry + :internal:71354a473744909de610943775f92038 LAST + S: 250 2.5.0 Address Ok. + S: 250 2.1.5 ron@gryffindor.example.com OK. + S: 554 5.7.0 IMAP URL authorization failed + +3.5. Formal Syntax + + The following syntax specification inherits ABNF [RFC4234] and + Uniform Resource Identifiers [RFC3986]. + + burl-param = "imap" / ("imap://" authority) + ; parameter to BURL EHLO keyword + + burl-cmd = "BURL" SP absolute-URI [SP end-marker] CRLF + + end-marker = "LAST" + + + + +Newman Standards Track [Page 6] + +RFC 4468 Message Submission BURL Extension May 2006 + + +4. 8-Bit and Binary + + A submit server that advertises BURL MUST also advertise 8BITMIME + [RFC1652] and perform the down conversion described in that + specification on the resulting complete message if 8-bit data is + received with the BURL command and passed to a 7-bit server. If the + URL argument to BURL refers to binary data, then the submit server + MAY refuse the command or down convert as described in Binary SMTP + [RFC3030]. + + The Submit server MAY refuse to accept a BURL command or combination + of BURL and BDAT commands that result in un-encoded 8-bit data in + mail or MIME [RFC2045] headers. Alternatively, the server MAY accept + such data and down convert to MIME header encoding [RFC2047]. + +5. Updates to RFC 3463 + + SMTP or Submit servers that advertise ENHANCEDSTATUSCODES [RFC2034] + use enhanced status codes defined in RFC 3463 [RFC3463]. The BURL + extension introduces new error cases that that RFC did not consider. + The following additional enhanced status codes are defined by this + specification: + + X.6.6 Message content not available + + The message content could not be fetched from a remote system. + This may be useful as a permanent or persistent temporary + notification. + + X.7.8 Trust relationship required + + The submission server requires a configured trust relationship + with a third-party server in order to access the message content. + +6. Response Codes + + This section includes example response codes to the BURL command. + Other text may be used with the same response codes. This list is + not exhaustive, and BURL clients MUST tolerate any valid SMTP + response code. Most of these examples include the appropriate + enhanced status code [RFC3463]. + + 554 5.5.0 No recipients have been specified + + This response code occurs when BURL is used (for example, with + PIPELINING) and all RCPT TOs failed. + + + + + +Newman Standards Track [Page 7] + +RFC 4468 Message Submission BURL Extension May 2006 + + + 503 5.5.0 Valid RCPT TO required before BURL + + This response code is an alternative to the previous one when BURL + is used (for example, with PIPELINING) and all RCPT TOs failed. + + 554 5.6.3 Conversion required but not supported + + This response code occurs when the URL points to binary data and + the implementation does not support down conversion to base64. + This can also be used if the URL points to message data with 8-bit + content in headers and the server does not down convert such + content. + + 554 5.3.4 Message too big for system + + The message (subsequent to URL resolution) is larger than the + per-message size limit for this server. + + 554 5.7.8 URL resolution requires trust relationship + + The submit server does not have a trust relationship with the IMAP + server specified in the URL argument to BURL. + + 552 5.2.2 Mailbox full + + The recipient is local, the submit server supports direct + delivery, and the recipient has exceeded his quota and any grace + period for delivery attempts. + + 554 5.6.6 IMAP URL resolution failed + + The IMAP URLFETCH command returned an error or no data. + + 250 2.5.0 Waiting for additional BURL or BDAT commands + + A BURL command without the "LAST" modifier was sent. The URL for + this BURL command was successfully resolved, but the content will + not necessarily be committed to persistent storage until the rest + of the message content is collected. For example, a Unix server + may have written the content to a queue file buffer, but may not + yet have performed an fsync() operation. If the server loses + power, the content can still be lost. + + 451 4.4.1 IMAP server unavailable + + The connection to the IMAP server to resolve the URL failed. + + + + + +Newman Standards Track [Page 8] + +RFC 4468 Message Submission BURL Extension May 2006 + + + 250 2.5.0 Ok. + + The URL was successfully resolved, and the complete message data + has been committed to persistent storage. + + 250 2.6.4 MIME header conversion with loss performed + + The URL pointed to message data that included mail or MIME headers + with 8-bit data. This data was converted to MIME header encoding + [RFC2047], but the submit server may not have correctly guessed + the unlabeled character set. + +7. IANA Considerations + + The "BURL" SMTP extension as described in Section 3 has been + registered. This registration has been marked for use by message + submission [RFC4409] only in the registry. + +8. Security Considerations + + Modern SMTP submission servers often include content-based security + and denial-of-service defense mechanisms such as virus filtering, + size limits, server-generated signatures, spam filtering, etc. + Implementations of BURL should fetch the URL content prior to + application of such content-based mechanisms in order to preserve + their function. + + Clients that generate unsolicited bulk email or email with viruses + could use this mechanism to compensate for a slow link between the + client and submit server. In particular, this mechanism would make + it feasible for a programmable cell phone or other device on a slow + link to become a significant source of unsolicited bulk email and/or + viruses. This makes it more important for submit server vendors + implementing BURL to have auditing and/or defenses against such + denial-of-service attacks including mandatory authentication, logging + that associates unique client identifiers with mail transactions, + limits on reuse of the same IMAP URL, rate limits, recipient count + limits, and content filters. + + Transfer of the URLAUTH [RFC4467] form of IMAP URLs in the clear can + expose the authorization token to network eavesdroppers. + Implementations that support such URLs can address this issue by + using a strong confidentiality protection mechanism. For example, + the SMTP STARTTLS [RFC3207] and the IMAP STARTTLS [RFC3501] + extensions, in combination with a configuration setting that requires + their use with such IMAP URLs, would address this concern. + + + + + +Newman Standards Track [Page 9] + +RFC 4468 Message Submission BURL Extension May 2006 + + + Use of a prearranged trust relationship between a submit server and a + specific IMAP server introduces security considerations. A + compromise of the submit server should not automatically compromise + all accounts on the IMAP server, so trust relationships involving + super-user proxy credentials are strongly discouraged. A system that + requires the submit server to authenticate to the IMAP server with + submit credentials and subsequently requires a URLAUTH URL to fetch + any content addresses this concern. A trusted third party model for + proxy credentials (such as that provided by Kerberos 5 [RFC4120]) + would also suffice. + + When a client uses SMTP STARTTLS to send a BURL command that + references non-public information, there is a user expectation that + the entire message content will be treated confidentially. To + address this expectation, the message submission server SHOULD use + STARTTLS or a mechanism providing equivalent data confidentiality + when fetching the content referenced by that URL. + + A legitimate user of a submit server may try to compromise other + accounts on the server by providing an IMAP URLAUTH URL that points + to a server under that user's control that is designed to undermine + the security of the submit server. For this reason, the IMAP client + code that the submit server uses must be robust with respect to + arbitrary input sizes (including large IMAP literals) and arbitrary + delays from the IMAP server. Requiring a prearranged trust + relationship between a submit server and the IMAP server also + addresses this concern. + + An authorized user of the submit server could set up a fraudulent + IMAP server and pass a URL for that server to the submit server. The + submit server might then contact the fraudulent IMAP server to + authenticate with submit credentials and fetch content. There are + several ways to mitigate this potential attack. A submit server that + only uses submit credentials with a fixed set of trusted IMAP servers + will not be vulnerable to exposure of those credentials. A submit + server can treat the IMAP server as untrusted and include defenses + for buffer overflows, denial-of-service slowdowns, and other + potential attacks. Finally, because authentication is required to + use BURL, it is possible to keep a secure audit trail and use that to + detect and punish the offending party. + + + + + + + + + + + +Newman Standards Track [Page 10] + +RFC 4468 Message Submission BURL Extension May 2006 + + +9. References + +9.1. Normative References + + [RFC1652] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D. + Crocker, "SMTP Service Extension for + 8bit-MIMEtransport", RFC 1652, July 1994. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2192] Newman, C., "IMAP URL Scheme", RFC 2192, + September 1997. + + [RFC2554] Myers, J., "SMTP Service Extension for Authentication", + RFC 2554, March 1999. + + [RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, + April 2001. + + [RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP + over Transport Layer Security", RFC 3207, + February 2002. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - + VERSION 4rev1", RFC 3501, March 2003. + + [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, + "Uniform Resource Identifier (URI): Generic Syntax", + STD 66, RFC 3986, January 2005. + + [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 4234, October 2005. + + [RFC4409] Gellens, R. and J. Klensin, "Message Submission for + Mail", RFC 4409, April 2006. + + [RFC4467] Crispin, M., "Internet Message Access Protocol (IMAP) - + URLAUTH Extension", RFC 4467, May 2006. + + + + + + + + + + + + +Newman Standards Track [Page 11] + +RFC 4468 Message Submission BURL Extension May 2006 + + +9.2. Informative References + + [RFC2034] Freed, N., "SMTP Service Extension for Returning + Enhanced Error Codes", RFC 2034, October 1996. + + [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet + Mail Extensions (MIME) Part One: Format of Internet + Message Bodies", RFC 2045, November 1996. + + [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail + Extensions) Part Three: Message Header Extensions for + Non-ASCII Text", RFC 2047, November 1996. + + [RFC2920] Freed, N., "SMTP Service Extension for Command + Pipelining", STD 60, RFC 2920, September 2000. + + [RFC3030] Vaudreuil, G., "SMTP Service Extensions for + Transmission of Large and Binary MIME Messages", + RFC 3030, December 2000. + + [RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes", + RFC 3463, January 2003. + + [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The + Kerberos Network Authentication Service (V5)", RFC + 4120, July 2005. + + [SASL-PLAIN] Zeilenga, K., "The Plain SASL Mechanism", Work in + Progress, March 2005. + + + + + + + + + + + + + + + + + + + + + + +Newman Standards Track [Page 12] + +RFC 4468 Message Submission BURL Extension May 2006 + + +Appendix A. Acknowledgements + + This document is a product of the lemonade WG. Many thanks are due + to all the participants of that working group for their input. Mark + Crispin was instrumental in the conception of this mechanism. Thanks + to Randall Gellens, Alexey Melnikov, Sam Hartman, Ned Freed, Dave + Cridland, Peter Coates, and Mark Crispin for review comments on the + document. Thanks to the RFC Editor for correcting the author's + grammar mistakes. Thanks to Ted Hardie, Randall Gellens, Mark + Crispin, Pete Resnick, and Greg Vaudreuil for extremely interesting + debates comparing this proposal and alternatives. Thanks to the + lemonade WG chairs Eric Burger and Glenn Parsons for concluding the + debate at the correct time and making sure this document got + completed. + +Author's Address + + Chris Newman + Sun Microsystems + 3401 Centrelake Dr., Suite 410 + Ontario, CA 91761 + US + + EMail: chris.newman@sun.com + + + + + + + + + + + + + + + + + + + + + + + + + + + +Newman Standards Track [Page 13] + +RFC 4468 Message Submission BURL Extension May 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + + + +Newman Standards Track [Page 14] + diff --git a/imap/docs/rfc/rfc4469.txt b/imap/docs/rfc/rfc4469.txt new file mode 100644 index 00000000..da365514 --- /dev/null +++ b/imap/docs/rfc/rfc4469.txt @@ -0,0 +1,731 @@ + + + + + + +Network Working Group P. Resnick +Request for Comments: 4469 QUALCOMM Incorporated +Updates: 3501, 3502 April 2006 +Category: Standards Track + + + Internet Message Access Protocol (IMAP) CATENATE Extension + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + The CATENATE extension to the Internet Message Access Protocol (IMAP) + extends the APPEND command to allow clients to create messages on the + IMAP server that may contain a combination of new data along with + parts of (or entire) messages already on the server. Using this + extension, the client can catenate parts of an already existing + message onto a new message without having to first download the data + and then upload it back to the server. + + + + + + + + + + + + + + + + + + + + + + +Resnick Standards Track [Page 1] + +RFC 4469 IMAP CATENATE Extension April 2006 + + +1. Introduction + + The CATENATE extension to the Internet Message Access Protocol (IMAP) + [1] allows the client to create a message on the server that can + include the text of messages (or parts of messages) that already + exist on the server without having to FETCH them and APPEND them back + to the server. The CATENATE extension extends the APPEND command so + that, instead of a single message literal, the command can take as + arguments any combination of message literals (as described in IMAP + [1]) and message URLs (as described in the IMAP URL Scheme [2] + specification). The server takes all the pieces and catenates them + into the output message. The CATENATE extension can also coexist + with the MULTIAPPEND extension [3] to APPEND multiple messages in a + single command. + + There are some obvious uses for the CATENATE extension. The + motivating use case was to provide a way for a resource-constrained + client to compose a message for subsequent submission that contains + data that already exists in that client's IMAP store. Because the + client does not have to download and re-upload potentially large + message parts, bandwidth and processing limitations do not have as + much impact. In addition, since the client can create a message in + its own IMAP store, the command also addresses the desire of the + client to archive a copy of a sent message without having to upload + the message twice. (Mechanisms for sending the message are outside + the scope of this document.) + + The extended APPEND command can also be used to copy parts of a + message to another mailbox for archival purposes while getting rid of + undesired parts. In environments where server storage is limited, a + client could get rid of large message parts by copying over only the + necessary parts and then deleting the original message. The + mechanism could also be used to add data to a message (such as + prepending message header fields) or to include other data by making + a copy of the original and catenating the new data. + +2. The CATENATE Capability + + A server that supports this extension returns "CATENATE" as one of + the responses to the CAPABILITY command. + + + + + + + + + + + +Resnick Standards Track [Page 2] + +RFC 4469 IMAP CATENATE Extension April 2006 + + +3. The APPEND Command + + Arguments: mailbox name + (The following can be repeated in the presence of the + MULTIAPPEND extension [3]) + OPTIONAL flag parenthesized list + OPTIONAL date/time string + a single message literal or one or more message parts to + catenate, specified as: + message literal + or + message (or message part) URL + + Responses: OPTIONAL NO responses: BADURL, TOOBIG + + Result: OK - append completed + NO - append error: can't append to that mailbox, error + in flags or date/time or message text, or can't + fetch that data + BAD - command unknown or arguments invalid + + The APPEND command concatenates all the message parts and appends + them as a new message to the end of the specified mailbox. The + parenthesized flag list and date/time string set the flags and the + internal date, respectively, as described in IMAP [1]. The + subsequent command parameters specify the message parts that are + appended sequentially to the output message. + + If the original form of APPEND is used, a message literal follows the + optional flag list and date/time string, which is appended as + described in IMAP [1]. If the extended form is used, "CATENATE" and + a parenthesized list of message literals and message URLs follows, + each of which is appended to the new message. If a message literal + is specified (indicated by "TEXT"), the octets following the count + are appended. If a message URL is specified (indicated by "URL"), + the octets of the body part pointed to by that URL are appended, as + if the literal returned in a FETCH BODY response were put in place of + the message part specifier. The APPEND command does not cause the + \Seen flag to be set for any catenated body part. The APPEND command + does not change the selected mailbox. + + In the extended APPEND command, the string following "URL" is an IMAP + URL [2] and is interpreted according to the rules of [2]. The + present document only describes the behavior of the command using + IMAP URLs that refer to specific messages or message parts on the + current IMAP server from the current authenticated IMAP session. + Because of that, only relative IMAP message or message part URLs + (i.e., those having no scheme or <iserver>) are used. The base URL + + + +Resnick Standards Track [Page 3] + +RFC 4469 IMAP CATENATE Extension April 2006 + + + for evaluating the relative URL is considered "imap://user@server/", + where "user" is the user name of the currently authenticated user and + "server" is the domain name of the current server. When in the + selected state, the base URL is considered + "imap://user@server/mailbox", where "mailbox" is the encoded name of + the currently selected mailbox. Additionally, since the APPEND + command is valid in the authenticated state of an IMAP session, no + further LOGIN or AUTHENTICATE command is performed for URLs specified + in the extended APPEND command. + + Note: Use of an absolute IMAP URL or any URL that refers to + anything other than a message or message part from the current + authenticated IMAP session is outside the scope of this document + and would require an extension to this specification, and a server + implementing only this specification would return NO to such a + request. + + The client is responsible for making sure that the catenated message + is in the format of an Internet Message Format (RFC 2822) [4] or + Multipurpose Internet Mail Extension (MIME) [5] message. In + particular, when a URL is catenated, the server copies octets, + unchanged, from the indicated message or message part to the + catenated message. It does no data conversion (e.g., MIME transfer + encodings) nor any verification that the data is appropriate for the + MIME part of the message into which it is inserted. The client is + also responsible for inserting appropriate MIME boundaries between + body parts, and writing MIME Content-Type and Content-Transfer- + Encoding lines as needed in the appropriate places. + + Responses behave just as the original APPEND command described in + IMAP [1]. If the server implements the IMAP UIDPLUS extension [6], + it will also return an APPENDUID response code in the tagged OK + response. Two response codes are provided in Section 4 that can be + used in the tagged NO response if the APPEND command fails. + +4. Response Codes + + When a APPEND command fails, it may return a response code that + describes a reason for the failure. + +4.1. BADURL Response + + The BADURL response code is returned if the APPEND fails to process + one of the specified URLs. Possible reasons for this are bad URL + syntax, unrecognized URL schema, invalid message UID, or invalid body + part. The BADURL response code contains the first URL specified as a + parameter to the APPEND command that has caused the operation to + fail. + + + +Resnick Standards Track [Page 4] + +RFC 4469 IMAP CATENATE Extension April 2006 + + +4.2. TOOBIG Response + + The TOOBIG response code is returned if the resulting message will + exceed the 4-GB IMAP message limit. This might happen, for example, + if the client specifies 3 URLs for 2-GB messages. Note that even if + the server doesn't return TOOBIG, it still has to be defensive + against misbehaving or malicious clients that try to construct a + message over the 4-GB limit. The server may also wish to return the + TOOBIG response code if the resulting message exceeds a server- + specific message size limit. + +5. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) [7] notation. Elements not defined here can be found in + the formal syntax of the ABNF [7], IMAP [1], and IMAP ABNF extensions + [8] specifications. Note that capability and resp-text-code are + extended from the IMAP [1] specification and append-data is extended + from the IMAP ABNF extensions [8] specification. + + append-data =/ "CATENATE" SP "(" cat-part *(SP cat-part) ")" + + cat-part = text-literal / url + + text-literal = "TEXT" SP literal + + url = "URL" SP astring + + resp-text-code =/ toobig-response-code / badurl-response-code + + toobig-response-code = "TOOBIG" + + badurl-response-code = "BADURL" SP url-resp-text + + url-resp-text = 1*(%x01-09 / + %x0B-0C / + %x0E-5B / + %x5D-FE) ; Any TEXT-CHAR except "]" + + capability =/ "CATENATE" + + The astring in the definition of url and the url-resp-text in the + definition of badurl-response-code each contain an imapurl as defined + by [2]. + + + + + + + +Resnick Standards Track [Page 5] + +RFC 4469 IMAP CATENATE Extension April 2006 + + +6. Acknowledgements + + Thanks to the members of the LEMONADE working group for their input. + Special thanks to Alexey Melnikov for the examples. + +7. Security Considerations + + The CATENATE extension does not raise any security considerations + that are not present for the base protocol or in the use of IMAP + URLs, and these issues are discussed in the IMAP [1] and IMAP URL [2] + documents. + +8. IANA Considerations + + IMAP4 capabilities are registered by publishing a standards track or + IESG approved experimental RFC. The registry is currently located at + <http://www.iana.org/assignments/imap4-capabilities>. This document + defines the CATENATE IMAP capability. The IANA has added this + capability to the registry. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Resnick Standards Track [Page 6] + +RFC 4469 IMAP CATENATE Extension April 2006 + + +Appendix A. Examples + + Lines not starting with "C: " or "S: " are continuations of the + previous lines. + + The original message in examples 1 and 2 below (UID = 20) has the + following structure: + + + multipart/mixed MIME message with two body parts: + + 1. text/plain + + 2. application/x-zip-compressed + + Example 1: The following example demonstrates how a CATENATE client + can replace an attachment in a draft message, without the need to + download it to the client and upload it back. + + C: A003 APPEND Drafts (\Seen \Draft $MDNSent) CATENATE + (URL "/Drafts;UIDVALIDITY=385759045/;UID=20/;section=HEADER" + TEXT {42} + S: + Ready for literal data + C: + C: --------------030308070208000400050907 + C: URL "/Drafts;UIDVALIDITY=385759045/;UID=20/;section=1.MIME" + URL "/Drafts;UIDVALIDITY=385759045/;UID=20/;section=1" TEXT {42} + S: + Ready for literal data + C: + C: --------------030308070208000400050907 + C: URL "/Drafts;UIDVALIDITY=385759045/;UID=30" TEXT {44} + S: + Ready for literal data + C: + C: --------------030308070208000400050907-- + C: ) + S: A003 OK catenate append completed + + + + + + + + + + + + + + + +Resnick Standards Track [Page 7] + +RFC 4469 IMAP CATENATE Extension April 2006 + + + Example 2: The following example demonstrates how the CATENATE + extension can be used to replace edited text in a draft message, as + well as header fields for the top level message part (e.g., Subject + has changed). The previous version of the draft is marked as + \Deleted. Note that the server also supports the UIDPLUS extension, + so the APPENDUID response code is returned in the successful OK + response to the APPEND command. + + C: A003 APPEND Drafts (\Seen \Draft $MDNSent) CATENATE (TEXT {738} + S: + Ready for literal data + C: Return-Path: <bar@example.org> + C: Received: from [127.0.0.2] + C: by rufus.example.org via TCP (internal) with ESMTPA; + C: Thu, 11 Nov 2004 16:57:07 +0000 + C: Message-ID: <419399E1.6000505@example.org> + C: Date: Thu, 12 Nov 2004 16:57:05 +0000 + C: From: Bob Ar <bar@example.org> + C: X-Accept-Language: en-us, en + C: MIME-Version: 1.0 + C: To: foo@example.net + C: Subject: About our holiday trip + C: Content-Type: multipart/mixed; + C: boundary="------------030308070208000400050907" + C: + C: --------------030308070208000400050907 + C: Content-Type: text/plain; charset=us-ascii; format=flowed + C: Content-Transfer-Encoding: 7bit + C: + C: Our travel agent has sent the updated schedule. + C: + C: Cheers, + C: Bob + C: --------------030308070208000400050907 + C: URL "/Drafts;UIDVALIDITY=385759045/;UID=20/;Section=2.MIME" + URL "/Drafts;UIDVALIDITY=385759045/;UID=20/;Section=2" TEXT {44} + S: + Ready for literal data + C: + C: --------------030308070208000400050907-- + C: ) + S: A003 OK [APPENDUID 385759045 45] append Completed + C: A004 UID STORE 20 +FLAGS.SILENT (\Deleted) + S: A004 OK STORE completed + + + + + + + + + +Resnick Standards Track [Page 8] + +RFC 4469 IMAP CATENATE Extension April 2006 + + + Example 3: The following example demonstrates how the CATENATE + extension can be used to strip attachments. Below, a PowerPoint + attachment was replaced by a small text part explaining that the + attachment was stripped. + + C: A003 APPEND Drafts (\Seen \Draft $MDNSent) CATENATE + (URL "/Drafts;UIDVALIDITY=385759045/;UID=21/;section=HEADER" + TEXT {42} + S: + Ready for literal data + C: + C: --------------030308070208000400050903 + C: URL "/Drafts;UIDVALIDITY=385759045/;UID=21/;section=1.MIME" + URL "/Drafts;UIDVALIDITY=385759045/;UID=21/;section=1" TEXT {255} + S: + Ready for literal data + C: + C: --------------030308070208000400050903 + C: Content-type: text/plain; charset="us-ascii" + C: Content-transfer-encoding: 7bit + C: + C: This body part contained a Power Point presentation that was + C: deleted upon your request. + C: --------------030308070208000400050903-- + C: ) + S: A003 OK append Completed + + + + + + + + + + + + + + + + + + + + + + + + + + + +Resnick Standards Track [Page 9] + +RFC 4469 IMAP CATENATE Extension April 2006 + + + Example 4: The following example demonstrates a failed APPEND + command. The server returns the BADURL response code to indicate + that one of the provided URLs is invalid. This example also + demonstrates how the CATENATE extension can be used to construct a + digest of several messages. + + C: A003 APPEND Sent (\Seen $MDNSent) CATENATE (TEXT {541} + S: + Ready for literal data + C: Return-Path: <foo@example.org> + C: Received: from [127.0.0.2] + C: by rufus.example.org via TCP (internal) with ESMTPA; + C: Thu, 11 Nov 2004 16:57:07 +0000 + C: Message-ID: <419399E1.6000505@example.org> + C: Date: Thu, 21 Nov 2004 16:57:05 +0000 + C: From: Farren Oo <foo@example.org> + C: X-Accept-Language: en-us, en + C: MIME-Version: 1.0 + C: To: bar@example.org + C: Subject: Digest of the mailing list for today + C: Content-Type: multipart/digest; + C: boundary="------------030308070208000400050904" + C: + C: --------------030308070208000400050904 + C: URL "/INBOX;UIDVALIDITY=785799047/;UID=11467" TEXT {42} + S: + Ready for literal data + C: + C: --------------030308070208000400050904 + C: URL "/INBOX;UIDVALIDITY=785799047/;UID=113330/;section=1.5.9" + TEXT {42} + S: + Ready for literal data + C: + C: --------------030308070208000400050904 + C: URL "/INBOX;UIDVALIDITY=785799047/;UID=11916" TEXT {44} + S: + Ready for literal data + C: + C: --------------030308070208000400050904-- + C: ) + S: A003 NO [BADURL "/INBOX;UIDVALIDITY=785799047/;UID=113330; + section=1.5.9"] CATENATE append has failed, one message expunged + + Note that the server could have validated the URLs as they were + received and therefore could have returned the tagged NO response + with BADURL response-code in place of any continuation request after + the URL was received. + + + + + + + +Resnick Standards Track [Page 10] + +RFC 4469 IMAP CATENATE Extension April 2006 + + +9. Normative References + + [1] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", + RFC 3501, March 2003. + + [2] Newman, C., "IMAP URL Scheme", RFC 2192, September 1997. + + [3] Crispin, M., "Internet Message Access Protocol (IMAP) - + MULTIAPPEND Extension", RFC 3502, March 2003. + + [4] Resnick, P., "Internet Message Format", RFC 2822, April 2001. + + [5] Freed, N. and N. Borenstein, "Multipurpose Internet Mail + Extensions (MIME) Part One: Format of Internet Message Bodies", + RFC 2045, November 1996. + + [6] Crispin, M., "Internet Message Access Protocol (IMAP) - UIDPLUS + extension", RFC 4315, December 2005. + + [7] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 4234, October 2005. + + [8] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4 ABNF", + RFC 4466, April 2006. + + + + + + + + + + + + + + + + + + + + + + + + + + + +Resnick Standards Track [Page 11] + +RFC 4469 IMAP CATENATE Extension April 2006 + + +Author's Address + + Peter W. Resnick + QUALCOMM Incorporated + 5775 Morehouse Drive + San Diego, CA 92121-1714 + US + + Phone: +1 858 651 4478 + EMail: presnick@qualcomm.com + URI: http://www.qualcomm.com/~presnick/ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Resnick Standards Track [Page 12] + +RFC 4469 IMAP CATENATE Extension April 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + + + +Resnick Standards Track [Page 13] + diff --git a/imap/docs/rfc/rfc4505.txt b/imap/docs/rfc/rfc4505.txt new file mode 100644 index 00000000..6b8a4a11 --- /dev/null +++ b/imap/docs/rfc/rfc4505.txt @@ -0,0 +1,507 @@ + + + + + + +Network Working Group K. Zeilenga, Ed. +Request for Comments: 4505 OpenLDAP Foundation +Obsoletes: 2245 June 2006 +Category: Standards Track + + + Anonymous Simple Authentication and Security Layer (SASL) Mechanism + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + On the Internet, it is common practice to permit anonymous access to + various services. Traditionally, this has been done with a plain- + text password mechanism using "anonymous" as the user name and using + optional trace information, such as an email address, as the + password. As plain-text login commands are not permitted in new IETF + protocols, a new way to provide anonymous login is needed within the + context of the Simple Authentication and Security Layer (SASL) + framework. + +1. Introduction + + This document defines an anonymous mechanism for the Simple + Authentication and Security Layer ([SASL]) framework. The name + associated with this mechanism is "ANONYMOUS". + + Unlike many other SASL mechanisms, whose purpose is to authenticate + and identify the user to a server, the purpose of this SASL mechanism + is to allow the user to gain access to services or resources without + requiring the user to establish or otherwise disclose their identity + to the server. That is, this mechanism provides an anonymous login + method. + + This mechanism does not provide a security layer. + + This document replaces RFC 2245. Changes since RFC 2245 are detailed + in Appendix A. + + + +Zeilenga Standards Track [Page 1] + +RFC 4505 Anonymous SASL Mechanism June 2006 + + +2. The Anonymous Mechanism + + The mechanism consists of a single message from the client to the + server. The client may include in this message trace information in + the form of a string of [UTF-8]-encoded [Unicode] characters prepared + in accordance with [StringPrep] and the "trace" stringprep profile + defined in Section 3 of this document. The trace information, which + has no semantical value, should take one of two forms: an Internet + email address, or an opaque string that does not contain the '@' + (U+0040) character and that can be interpreted by the system + administrator of the client's domain. For privacy reasons, an + Internet email address or other information identifying the user + should only be used with permission from the user. + + A server that permits anonymous access will announce support for the + ANONYMOUS mechanism and allow anyone to log in using that mechanism, + usually with restricted access. + + A formal grammar for the client message using Augmented BNF [ABNF] is + provided below as a tool for understanding this technical + specification. + + message = [ email / token ] + ;; to be prepared in accordance with Section 3 + + UTF1 = %x00-3F / %x41-7F ;; less '@' (U+0040) + UTF2 = %xC2-DF UTF0 + UTF3 = %xE0 %xA0-BF UTF0 / %xE1-EC 2(UTF0) / + %xED %x80-9F UTF0 / %xEE-EF 2(UTF0) + UTF4 = %xF0 %x90-BF 2(UTF0) / %xF1-F3 3(UTF0) / + %xF4 %x80-8F 2(UTF0) + UTF0 = %x80-BF + + TCHAR = UTF1 / UTF2 / UTF3 / UTF4 + ;; any UTF-8 encoded Unicode character + ;; except '@' (U+0040) + + email = addr-spec + ;; as defined in [IMAIL] + + token = 1*255TCHAR + + Note to implementors: + The <token> production is restricted to 255 UTF-8-encoded Unicode + characters. As the encoding of a characters uses a sequence of 1 + to 4 octets, a token may be as long as 1020 octets. + + + + + +Zeilenga Standards Track [Page 2] + +RFC 4505 Anonymous SASL Mechanism June 2006 + + +3. The "trace" Profile of "Stringprep" + + This section defines the "trace" profile of [StringPrep]. This + profile is designed for use with the SASL ANONYMOUS Mechanism. + Specifically, the client is to prepare the <message> production in + accordance with this profile. + + The character repertoire of this profile is Unicode 3.2 [Unicode]. + + No mapping is required by this profile. + + No Unicode normalization is required by this profile. + + The list of unassigned code points for this profile is that provided + in Appendix A of [StringPrep]. Unassigned code points are not + prohibited. + + Characters from the following tables of [StringPrep] are prohibited: + + - C.2.1 (ASCII control characters) + - C.2.2 (Non-ASCII control characters) + - C.3 (Private use characters) + - C.4 (Non-character code points) + - C.5 (Surrogate codes) + - C.6 (Inappropriate for plain text) + - C.8 (Change display properties are deprecated) + - C.9 (Tagging characters) + + No additional characters are prohibited. + + This profile requires bidirectional character checking per Section 6 + of [StringPrep]. + +4. Example + + Here is a sample ANONYMOUS login between an IMAP client and server. + In this example, "C:" and "S:" indicate lines sent by the client and + server, respectively. If such lines are wrapped without a new "C:" + or "S:" label, then the wrapping is for editorial clarity and is not + part of the command. + + Note that this example uses the IMAP profile [IMAP4] of SASL. The + base64 encoding of challenges and responses as well as the "+ " + preceding the responses are part of the IMAP4 profile, not part of + SASL itself. Additionally, protocols with SASL profiles permitting + an initial client response will be able to avoid the extra round trip + below (the server response with an empty "+ "). + + + + +Zeilenga Standards Track [Page 3] + +RFC 4505 Anonymous SASL Mechanism June 2006 + + + In this example, the trace information is "sirhc". + + S: * OK IMAP4 server ready + C: A001 CAPABILITY + S: * CAPABILITY IMAP4 IMAP4rev1 AUTH=DIGEST-MD5 AUTH=ANONYMOUS + S: A001 OK done + C: A002 AUTHENTICATE ANONYMOUS + S: + + C: c2lyaGM= + S: A003 OK Welcome, trace information has been logged. + +5. Security Considerations + + The ANONYMOUS mechanism grants access to services and/or resources by + anyone. For this reason, it should be disabled by default so that + the administrator can make an explicit decision to enable it. + + If the anonymous user has any write privileges, a denial-of-service + attack is possible by filling up all available space. This can be + prevented by disabling all write access by anonymous users. + + If anonymous users have read and write access to the same area, the + server can be used as a communication mechanism to exchange + information anonymously. Servers that accept anonymous submissions + should implement the common "drop box" model, which forbids anonymous + read access to the area where anonymous submissions are accepted. + + If the anonymous user can run many expensive operations (e.g., an + IMAP SEARCH BODY command), this could enable a denial-of-service + attack. Servers are encouraged to reduce the priority of anonymous + users or limit their resource usage. + + While servers may impose a limit on the number of anonymous users, + note that such limits enable denial-of-service attacks and should be + used with caution. + + The trace information is not authenticated, so it can be falsified. + This can be used as an attempt to get someone else in trouble for + access to questionable information. Administrators investigating + abuse need to realize that this trace information may be falsified. + + A client that uses the user's correct email address as trace + information without explicit permission may violate that user's + privacy. Anyone who accesses an anonymous archive on a sensitive + subject (e.g., sexual abuse) likely has strong privacy needs. + Clients should not send the email address without the explicit + permission of the user and should offer the option of supplying no + trace information, thus only exposing the source IP address and time. + + + +Zeilenga Standards Track [Page 4] + +RFC 4505 Anonymous SASL Mechanism June 2006 + + + Anonymous proxy servers could enhance this privacy but would have to + consider the resulting potential denial-of-service attacks. + + Anonymous connections are susceptible to man-in-the-middle attacks + that view or alter the data transferred. Clients and servers are + encouraged to support external data security services. + + Protocols that fail to require an explicit anonymous login are more + susceptible to break-ins given certain common implementation + techniques. Specifically, Unix servers that offer user login may + initially start up as root and switch to the appropriate user id + after an explicit login command. Normally, such servers refuse all + data access commands prior to explicit login and may enter a + restricted security environment (e.g., the Unix chroot(2) function) + for anonymous users. If anonymous access is not explicitly + requested, the entire data access machinery is exposed to external + security attacks without the chance for explicit protective measures. + Protocols that offer restricted data access should not allow + anonymous data access without an explicit login step. + + General [SASL] security considerations apply to this mechanism. + + [StringPrep] security considerations and [Unicode] security + considerations discussed in [StringPrep] apply to this mechanism. + [UTF-8] security considerations also apply. + +6. IANA Considerations + + The SASL Mechanism registry [IANA-SASL] entry for the ANONYMOUS + mechanism has been updated by the IANA to reflect that this document + now provides its technical specification. + + To: iana@iana.org + Subject: Updated Registration of SASL mechanism ANONYMOUS + + SASL mechanism name: ANONYMOUS + Security considerations: See RFC 4505. + Published specification (optional, recommended): RFC 4505 + Person & email address to contact for further information: + Kurt Zeilenga <Kurt@OpenLDAP.org> + Chris Newman <Chris.Newman@sun.com> + Intended usage: COMMON + Author/Change controller: IESG <iesg@ietf.org> + Note: Updates existing entry for ANONYMOUS + + + + + + + +Zeilenga Standards Track [Page 5] + +RFC 4505 Anonymous SASL Mechanism June 2006 + + + The [StringPrep] profile "trace", first defined in this RFC, has been + registered: + + To: iana@iana.org + Subject: Initial Registration of Stringprep "trace" profile + + Stringprep profile: trace + Published specification: RFC 4505 + Person & email address to contact for further information: + Kurt Zeilenga <kurt@openldap.org> + +7. Acknowledgement + + This document is a revision of RFC 2245 by Chris Newman. Portions of + the grammar defined in Section 1 were borrowed from RFC 3629 by + Francois Yergeau. + + This document is a product of the IETF SASL WG. + +8. Normative References + + [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 4234, October 2005. + + [IMAIL] Resnick, P., "Internet Message Format", RFC 2822, April + 2001. + + [SASL] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple + Authentication and Security Layer (SASL)", RFC 4422, + June 2006. + + [StringPrep] Hoffman, P. and M. Blanchet, "Preparation of + Internationalized Strings ('stringprep')", RFC 3454, + December 2002. + + [Unicode] The Unicode Consortium, "The Unicode Standard, Version + 3.2.0" is defined by "The Unicode Standard, Version 3.0" + (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5), + as amended by the "Unicode Standard Annex #27: Unicode + 3.1" (http://www.unicode.org/reports/tr27/) and by the + "Unicode Standard Annex #28: Unicode 3.2" + (http://www.unicode.org/reports/tr28/). + + [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO + 10646", RFC 3629 (also STD 63), November 2003. + + + + + + +Zeilenga Standards Track [Page 6] + +RFC 4505 Anonymous SASL Mechanism June 2006 + + +9. Informative References + + [IMAP4] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [IANA-SASL] IANA, "SIMPLE AUTHENTICATION AND SECURITY LAYER (SASL) + MECHANISMS", <http://www.iana.org/assignments/sasl- + mechanisms>. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Zeilenga Standards Track [Page 7] + +RFC 4505 Anonymous SASL Mechanism June 2006 + + +Appendix A. Changes since RFC 2245 + + This appendix is non-normative. + + RFC 2245 allows the client to include optional trace information in + the form of a human readable string. RFC 2245 restricted this string + to US-ASCII. As the Internet is international, this document uses a + string restricted to UTF-8 encoded Unicode characters. A + "stringprep" profile is defined to precisely define which Unicode + characters are allowed in this string. While the string remains + restricted to 255 characters, the encoded length of each character + may now range from 1 to 4 octets. + + Additionally, a number of editorial changes were made. + +Editor's Address + + Kurt D. Zeilenga + OpenLDAP Foundation + + EMail: Kurt@OpenLDAP.org + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Zeilenga Standards Track [Page 8] + +RFC 4505 Anonymous SASL Mechanism June 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + + + +Zeilenga Standards Track [Page 9] + diff --git a/imap/docs/rfc/rfc4549.txt b/imap/docs/rfc/rfc4549.txt new file mode 100644 index 00000000..8430ee10 --- /dev/null +++ b/imap/docs/rfc/rfc4549.txt @@ -0,0 +1,1963 @@ + + + + + + +Network Working Group A. Melnikov, Ed. +Request for Comments: 4549 Isode Ltd. +Category: Informational June 2006 + + + Synchronization Operations for Disconnected IMAP4 Clients + +Status of This Memo + + This memo provides information for the Internet community. It does + not specify an Internet standard of any kind. Distribution of this + memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + This document attempts to address some of the issues involved in + building a disconnected IMAP4 client. In particular, it deals with + the issues of what might be called the "driver" portion of the + synchronization tool: the portion of the code responsible for issuing + the correct set of IMAP4 commands to synchronize the disconnected + client in the way that is most likely to make the human who uses the + disconnected client happy. + + This note describes different strategies that can be used by + disconnected clients and shows how to use IMAP protocol in order to + minimize the time of the synchronization process. + + This note also lists IMAP extensions that a server should implement + in order to provide better synchronization facilities to disconnected + clients. + + + + + + + + + + + + + + + + + +Melnikov Informational [Page 1] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + +Table of Contents + + 1. Introduction ....................................................3 + 1.1. Conventions Used in This Document ..........................3 + 2. Design Principles ...............................................3 + 3. Overall Picture of Synchronization ..............................4 + 4. Mailbox Synchronization Steps and Strategies ....................7 + 4.1. Checking UID Validity ......................................7 + 4.2. Synchronizing Local Changes with the Server ................8 + 4.2.1. Uploading Messages to the Mailbox ...................8 + 4.2.2. Optimizing "move" and "copy" Operations .............9 + 4.2.3. Replaying Local Flag Changes .......................14 + 4.2.4. Processing Mailbox Compression (EXPUNGE) Requests ..15 + 4.2.5. Closing a Mailbox ..................................17 + 4.3. Details of "Normal" Synchronization of a Single Mailbox ...18 + 4.3.1. Discovering New Messages and Changes to Old + Messages ...........................................18 + 4.3.2. Searching for "Interesting" Messages. ..............20 + 4.3.3. Populating Cache with "Interesting" Messages. ......21 + 4.3.4. User-Initiated Synchronization .....................22 + 4.4. Special Case: Descriptor-Only Synchronization .............22 + 4.5. Special Case: Fast New-Only Synchronization ...............23 + 4.6. Special Case: Blind FETCH .................................23 + 5. Implementation Considerations ..................................24 + 5.1. Error Recovery during Playback ............................26 + 5.2. Quality of Implementation Issues ..........................28 + 5.3. Optimizations .............................................28 + 6. IMAP Extensions That May Help ..................................30 + 6.1. CONDSTORE Extension .......................................30 + 7. Security Considerations ........................................33 + 8. References .....................................................33 + 8.1. Normative References ......................................33 + 8.2. Informative References ....................................34 + 9. Acknowledgements ...............................................34 + + + + + + + + + + + + + + + + + +Melnikov Informational [Page 2] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + +1. Introduction + + Several recommendations presented in this document are generally + applicable to all types of IMAP clients. However, this document + tries to concentrate on disconnected mail clients [IMAP-MODEL]. It + also suggests some IMAP extensions* that should be implemented by + IMAP servers in order to make the life of disconnected clients + easier. In particular, the [UIDPLUS] extension was specifically + designed to streamline certain disconnected operations, like + expunging, uploading, and copying messages (see Sections 4.2.1, + 4.2.2.1, and 4.2.4). + + Readers of this document are also strongly advised to read RFC 2683 + [RFC2683]. + + * Note that the functionality provided by the base IMAP protocol + [IMAP4] is sufficient to perform basic synchronization. + +1.1. Conventions Used in This Document + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. Long lines in examples are broken for + editorial clarity. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [KEYWORDS]. + + Let's call an IMAP command idempotent if the result of executing the + command twice sequentially is the same as the result of executing the + command just once. + +2. Design Principles + + All mailbox state or content information stored on the disconnected + client should be viewed strictly as a cache of the state of the + server. The "master" state remains on the server, just as it would + with an interactive IMAP4 client. The one exception to this rule is + that information about the state of the disconnected client's cache + (the state includes flag changes while offline and during scheduled + message uploads) remains on the disconnected client: that is, the + IMAP4 server is not responsible for remembering the state of the + disconnected IMAP4 client. + + We assume that a disconnected client is a client that, for whatever + reason, wants to minimize the length of time that it is "on the + phone" to the IMAP4 server. Often this will be because the client is + using a dialup connection, possibly with very low bandwidth, but + + + +Melnikov Informational [Page 3] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + sometimes it might just be that the human is in a hurry to catch an + airplane, or some other event beyond our control. Whatever the + reason, we assume that we must make efficient use of the network + connection, both in the usual sense (not generating spurious traffic) + and in the sense that we would prefer not to have the connection + sitting idle while the client and/or the server is performing + strictly local computation or I/O. Another, perhaps simpler way of + stating this is that we assume that network connections are + "expensive". + + Practical experience with disconnected mail systems has shown that + there is no single synchronization strategy that is appropriate for + all cases. Different humans have different preferences, and the same + human's preference will vary depending both on external circumstance + (how much of a hurry the human is in today) and on the value that the + human places on the messages being transferred. The point here is + that there is no way that the synchronization program can guess + exactly what the human wants to do, so the human will have to provide + some guidance. + + Taken together, the preceding two principles lead to the conclusion + that the synchronization program must make its decisions based on + some kind of guidance provided by the human, by selecting the + appropriate options in the user interface or through some sort of + configuration file. Almost certainly, it should not pause for I/O + with the human in the middle of the synchronization process. The + human will almost certainly have several different configurations for + the synchronization program, for different circumstances. + + Since a disconnected client has no way of knowing what changes might + have occurred to the mailbox while it was disconnected, message + numbers are not useful to a disconnected client. All disconnected + client operations should be performed using UIDs, so that the client + can be sure that it and the server are talking about the same + messages during the synchronization process. + +3. Overall Picture of Synchronization + + The basic strategy for synchronization is outlined below. Note that + the real strategy may vary from one application to another or may + depend on a synchronization mode. + + a) Process any "actions" that were pending on the client that were + not associated with any mailbox. (In particular sending messages + composed offline with SMTP. This is not part of IMAP + synchronization, but it is mentioned here for completeness.) + + + + + +Melnikov Informational [Page 4] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + b) Fetch the current list of "interesting" mailboxes. (The + disconnected client should allow the user to skip this step + completely.) + + c) "Client-to-server synchronization": for each IMAP "action" that + was pending on the client, do the following: + + 1) If the action implies opening a new mailbox (any operation that + operates on messages), open the mailbox. Check its UID + validity value (see Section 4.1 for more details) returned in + the UIDVALIDITY response code. If the UIDVALIDITY value + returned by the server differs, the client MUST empty the local + cache of the mailbox and remove any pending "actions" that + refer to UIDs in that mailbox (and consider them failed). Note + that this doesn't affect actions performed on client-generated + fake UIDs (see Section 5). + + 2) Perform the action. If the action is to delete a mailbox + (DELETE), make sure that the mailbox is closed first (see also + Section 3.4.12 of [RFC2683]). + + d) "Server-to-client synchronization": for each mailbox that requires + synchronization, do the following: + + 1) Check the mailbox UIDVALIDITY (see Section 4.1 for more + details) with SELECT/EXAMINE/STATUS. + + If UIDVALIDITY value returned by the server differs, the client + MUST + + * empty the local cache of that mailbox; + * remove any pending "actions" that refer to UIDs in that + mailbox and consider them failed; and + * skip step 2-II. + + 2) Fetch the current "descriptors"; + + I) Discover new messages. + + II) Discover changes to old messages. + + 3) Fetch the bodies of any "interesting" messages that the client + doesn't already have. + + e) Close all open mailboxes not required for further operations (if + staying online) or disconnect all open connections (if going + offline). + + + + +Melnikov Informational [Page 5] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + Terms used: + + "Actions" are queued requests that were made by the human to the + client's Mail User Agent (MUA) software while the client was + disconnected. + + We define "descriptors" as a set of IMAP4 FETCH data items. + Conceptually, a message's descriptor is that set of information that + allows the synchronization program to decide what protocol actions + are necessary to bring the local cache to the desired state for this + message; since this decision is really up to the human, this + information probably includes at least a few header fields intended + for human consumption. Exactly what will constitute a descriptor + depends on the client implementation. At a minimum, the descriptor + contains the message's UID and FLAGS. Other likely candidates are + the RFC822.SIZE, RFC822.HEADER, BODYSTRUCTURE, or ENVELOPE data + items. + + Comments: + + 1) The list of actions should be ordered. For example, if the human + deletes message A1 in mailbox A, then expunges mailbox A, and then + deletes message A2 in mailbox A, the human will expect that + message A1 is gone and that message A2 is still present but is now + deleted. + + By processing all the actions before proceeding with + synchronization, we avoid having to compensate for the local MUA's + changes to the server's state. That is, once we have processed + all the pending actions, the steps that the client must take to + synchronize itself will be the same no matter where the changes to + the server's state originated. + + 2) Steps a and b can be performed in parallel. Alternatively, step a + can be performed after d. + + 3) On step b, the set of "interesting" mailboxes pretty much has to + be determined by the human. What mailboxes belong to this set may + vary between different IMAP4 sessions with the same server, + client, and human. An interesting mailbox can be a mailbox + returned by LSUB command (see Section 6.3.9 of [IMAP4]). The + special mailbox "INBOX" SHOULD be in the default set of mailboxes + that the client considers interesting. However, providing the + ability to ignore INBOX for a particular session or client may be + valuable for some mail filtering strategies. + + + + + + +Melnikov Informational [Page 6] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + 4) On step d-2-II, the client also finds out about changes to the + flags of messages that the client already has in its local cache, + and about messages in the local cache that no longer exist on the + server (i.e., messages that have been expunged). + + 5) "Interesting" messages are those messages that the synchronization + program thinks the human wants to have cached locally, based on + the configuration and the data retrieved in step b. + + 6) A disconnected IMAP client is a special case of an IMAP client, so + it MUST be able to handle any "unexpected" unsolicited responses, + like EXISTS and EXPUNGE, at any time. The disconnected client MAY + ignore EXPUNGE response during "client-to-server" synchronization + phase (step c). + + The rest of this discussion will focus primarily on the + synchronization issues for a single mailbox. + +4. Mailbox Synchronization Steps and Strategies + +4.1. Checking UID Validity + + The "UID validity" of a mailbox is a number returned in an + UIDVALIDITY response code in an OK untagged response at mailbox + selection time. The UID validity value changes between sessions when + UIDs fail to persist between sessions. + + Whenever the client selects a mailbox, the client must compare the + returned UID validity value with the value stored in the local cache. + If the UID validity values differ, the UIDs in the client's cache are + no longer valid. The client MUST then empty the local cache of that + mailbox and remove any pending "actions" that refer to UIDs in that + mailbox. The client MAY also issue a warning to the human. The + client MUST NOT cancel any scheduled uploads (i.e., APPENDs) for the + mailbox. + + Note that UIDVALIDITY is not only returned on a mailbox selection. + The COPYUID and APPENDUID response codes defined in the [UIDPLUS] + extension (see also 4.2.2) and the UIDVALIDITY STATUS response data + item also contain a UIDVALIDITY value for some other mailbox. The + client SHOULD behave as described in the previous paragraph (but it + should act on the other mailbox's cache), no matter how it obtained + the UIDVALIDITY value. + + + + + + + + +Melnikov Informational [Page 7] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + +4.2. Synchronizing Local Changes with the Server + +4.2.1. Uploading Messages to the Mailbox + + Two of the most common examples of operations resulting in message + uploads are: + + 1) Saving a draft message + + 2) Copying a message between remote mailboxes on two different IMAP + servers or a local mailbox and a remote mailbox. + + Message upload is performed with the APPEND command. A message + scheduled to be uploaded has no UID associated with it, as all UIDs + are assigned by the server. The APPEND command will effectively + associate a UID with the uploaded message that can be stored in the + local cache for future reference. However, [IMAP4] doesn't describe + a simple mechanism to discover the message UID by just performing the + APPEND command. In order to discover the UID, the client can do one + of the following: + + 1) Remove the uploaded message from cache. Then, use the mechanism + described in 4.3 to fetch the information about the uploaded + message as if it had been uploaded by some other client. + + 2) Try to fetch header information as described in 4.2.2 in order to + find a message that corresponds to the uploaded message. One + strategy for doing this is described in 4.2.2. + + Case 1 describes a not particularly smart client. + + C: A003 APPEND Drafts (\Seen $MDNSent) {310} + S: + Ready for literal data + C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST) + C: From: Fred Foobar <foobar@blt.example.COM> + C: Subject: afternoon meeting + C: To: mooch@owatagu.siam.edu + C: Message-Id: <B27397-0100000@blt.example.COM> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: Hello Joe, do you think we can meet at 3:30 tomorrow? + C: + S: A003 OK APPEND Completed + + Fortunately, there is a simpler way to discover the message UID in + the presence of the [UIDPLUS] extension: + + + + +Melnikov Informational [Page 8] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + C: A003 APPEND Drafts (\Seen $MDNSent) {310} + S: + Ready for literal data + C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST) + C: From: Fred Foobar <foobar@blt.example.COM> + C: Subject: afternoon meeting + C: To: mooch@owatagu.siam.edu + C: Message-Id: <B27397-0100000@blt.example.COM> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: Hello Joe, do you think we can meet at 3:30 tomorrow? + C: + S: A003 OK [APPENDUID 1022843275 77712] APPEND completed + + The UID of the appended message is the second parameter of APPENDUID + response code. + +4.2.2. Optimizing "move" and "copy" Operations + + Practical experience with IMAP and other mailbox access protocols + that support multiple mailboxes suggests that moving a message from + one mailbox to another is an extremely common operation. + +4.2.2.1. Moving a Message between Two Mailboxes on the Same Server + + In IMAP4, a "move" operation between two mailboxes on the same server + is really a combination of a COPY operation and a STORE +FLAGS + (\Deleted) operation. This makes good protocol sense for IMAP, but + it leaves a simple-minded disconnected client in the silly position + of deleting and possibly expunging its cached copy of a message, then + fetching an identical copy via the network. + + However, the presence of the UIDPLUS extension in the server can + help: + + C: A001 UID COPY 567,414 "Interesting Messages" + S: A001 OK [COPYUID 1022843275 414,567 5:6] Completed + + This tells the client that the message with UID 414 in the current + mailbox was successfully copied to the mailbox "Interesting Messages" + and was given the UID 5, and that the message with UID 567 was given + the UID 6. + + In the absence of UIDPLUS extension support in the server, the + following trick can be used. By including the Message-ID: header and + the INTERNALDATE data item as part of the descriptor, the client can + check the descriptor of a "new" message against messages that are + already in its cache and avoid fetching the extra copy. Of course, + + + +Melnikov Informational [Page 9] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + it's possible that the cost of checking to see if the message is + already in the local cache may exceed the cost of just fetching it, + so this technique should not be used blindly. If the MUA implements + a "move" command, it makes special provisions to use this technique + when it knows that a copy/delete sequence is the result of a "move" + command. + + Note that servers are not required (although they are strongly + encouraged with "SHOULD language") to preserve INTERNALDATE when + copying messages. + + Also note that since it's theoretically possible for this algorithm + to find the wrong message (given sufficiently malignant Message-ID + headers), implementers should provide a way to disable this + optimization, both permanently and on a message-by-message basis. + + Example 1: Copying a message in the absence of UIDPLUS extension. + + At some point in time the client has fetched the source message and + some information was cached: + + C: C021 UID FETCH <uids> (BODY.PEEK[] INTERNALDATE FLAGS) + ... + S: * 27 FETCH (UID 123 INTERNALDATE "31-May-2002 05:26:59 -0600" + FLAGS (\Draft $MDNSent) BODY[] {1036} + S: ... + S: Message-Id: <20040903110856.22a127cd@chardonnay> + S: ... + S: ...message body... + S: ) + ... + S: C021 OK fetch completed + + Later on, the client decides to copy the message: + + C: C035 UID COPY 123 "Interesting Messages" + S: C035 OK Completed + + As the server hasn't provided the COPYUID response code, the client + tries the optimization described above: + + C: C036 SELECT "Interesting Messages" + ... + C: C037 UID SEARCH ON 31-May-2002 HEADER + "Message-Id" "20040903110856.22a127cd@chardonnay" + S: SEARCH 12368 + S: C037 OK completed + + + + +Melnikov Informational [Page 10] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + Note that if the server has returned multiple UIDs in the SEARCH + response, the client MUST NOT use any of the returned UID. + +4.2.2.2. Moving a Message from a Remote Mailbox to a Local + + Moving a message from a remote mailbox to a local is done with FETCH + (that includes FLAGS and INTERNALDATE) followed by UID STORE <uid> + +FLAGS.SILENT (\Deleted): + + C: A003 UID FETCH 123 (BODY.PEEK[] INTERNALDATE FLAGS) + S: * 27 FETCH (UID 123 INTERNALDATE "31-May-2002 05:26:59 -0600" + FLAGS (\Seen $MDNSent) BODY[] + S: ...message body... + S: ) + S: A003 OK UID FETCH completed + C: A004 UID STORE <uid> +FLAGS.SILENT (\Deleted) + S: A004 STORE completed + + Note that there is no reason to fetch the message during + synchronization if it's already in the client's cache. Also, the + client SHOULD preserve delivery date in the local cache. + +4.2.2.3. Moving a Message from a Local Mailbox to a Remote + + Moving a message from a local mailbox to a remote is done with + APPEND: + + C: A003 APPEND Drafts (\Seen $MDNSent) "31-May-2002 05:26:59 -0600" + {310} + S: + Ready for literal data + C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST) + C: From: Fred Foobar <foobar@blt.example.COM> + C: Subject: afternoon meeting + C: To: mooch@owatagu.siam.edu + C: Message-Id: <B27397-0100000@blt.example.COM> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: Hello Joe, do you think we can meet at 3:30 tomorrow? + C: + S: A003 OK [APPENDUID 1022843275 77712] completed + + The client SHOULD specify the delivery date from the local cache in + the APPEND. + + If the [LITERAL+] extension is available, the client can save a + round-trip*: + + + + +Melnikov Informational [Page 11] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + C: A003 APPEND Drafts (\Seen $MDNSent) "31-May-2002 05:26:59 -0600" + {310+} + C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST) + C: From: Fred Foobar <foobar@blt.example.COM> + C: Subject: afternoon meeting + C: To: mooch@owatagu.siam.edu + C: Message-Id: <B27397-0100000@blt.example.COM> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: Hello Joe, do you think we can meet at 3:30 tomorrow? + C: + S: A003 OK [APPENDUID 1022843275 77712] completed + + * Note that there is a risk that the server will reject the message + due to its size. If this happens, the client will waste bandwidth + transferring the whole message. If the client wouldn't have used + the LITERAL+, this could have been avoided: + + C: A003 APPEND Drafts (\Seen $MDNSent) "31-May-2004 05:26:59 -0600" + {16777215} + S: A003 NO Sorry, message is too big + +4.2.2.4. Moving a Message between Two Mailboxes on Different Servers + + Moving a message between two mailbox on two different servers is a + combination of the operations described in 4.2.2.2 followed by the + operations described in 4.2.2.3. + +4.2.2.5. Uploading Multiple Messages to a Remote Mailbox with + MULTIAPPEND + + When there is a need to upload multiple messages to a remote mailbox + (e.g., as per 4.2.2.3), the presence of certain IMAP extensions may + significantly improve performance. One of them is [MULTIAPPEND]. + + For some mail stores, opening a mailbox for appending might be + expensive. [MULTIAPPEND] tells the server to open the mailbox once + (instead of opening and closing it "n" times per "n" messages to be + uploaded) and to keep it open while a group of messages is being + uploaded to the server. + + Also, if the server supports both [MULTIAPPEND] and [LITERAL+] + extensions, the entire upload is accomplished in a single + command/response round-trip. + + + + + + +Melnikov Informational [Page 12] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + Note: Client implementers should be aware that [MULTIAPPEND] performs + append of multiple messages atomically. This means, for example, if + there is not enough space to save "n"-th message (or the message has + invalid structure and is rejected by the server) after successful + upload of "n-1" messages, the whole upload operation fails, and no + message will be saved in the mailbox. Although this behavior might + be desirable in certain situations, it might not be what you want. + Otherwise, the client should use the regular APPEND command (Section + 4.2.2.3), possibly utilizing the [LITERAL+] extension. See also + Section 5.1 for discussions about error recovery. + + Note: MULTIAPPEND can be used together with the UIDPLUS extension in + a way similar to what was described in Section 4.2.1. [MULTIAPPEND] + extends the syntax of the APPENDUID response code to allow for + multiple message UIDs in the second parameter. + + Example 2: + + This example demonstrates the use of MULTIAPPEND together with + UIDPLUS (synchronization points where the client waits for + confirmations from the server are marked with "<--->"): + + C: A003 APPEND Jan-2002 (\Seen $MDNSent) "31-May-2002 05:26:59 -0600" + {310} + <---> + S: + Ready for literal data + C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST) + C: From: Fred Foobar <foobar@blt.example.COM> + C: Subject: afternoon meeting + C: To: mooch@owatagu.siam.edu + C: Message-Id: <B27397-0100000@blt.example.COM> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: Hello Joe, do you think we can meet at 3:30 tomorrow? + C: (\Seen) " 1-Jun-2002 22:43:04 -0800" {286} + <---> + S: + Ready for literal data + C: Date: Mon, 7 Feb 1994 22:43:04 -0800 (PST) + C: From: Joe Mooch <mooch@OWaTaGu.siam.EDU> + C: Subject: Re: afternoon meeting + C: To: foobar@blt.example.com + C: Message-Id: <a0434793874930@OWaTaGu.siam.EDU> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: 3:30 is fine with me. + C: + + + +Melnikov Informational [Page 13] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + S: A003 OK [APPENDUID 1022843275 77712,77713] completed + + The upload takes 3 round-trips. + + Example 3: + + In this example, Example 2 was modified for the case when the server + supports MULTIAPPEND, LITERAL+, and UIDPLUS. The upload takes only 1 + round-trip. + + C: A003 APPEND Jan-2002 (\Seen $MDNSent) "31-May-2002 05:26:59 -0600" + {310+} + C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST) + C: From: Fred Foobar <foobar@blt.example.COM> + C: Subject: afternoon meeting + C: To: mooch@owatagu.siam.edu + C: Message-Id: <B27397-0100000@blt.example.COM> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: Hello Joe, do you think we can meet at 3:30 tomorrow? + C: (\Seen) " 1-Jun-2002 22:43:04 -0800" {286+} + C: Date: Mon, 7 Feb 1994 22:43:04 -0800 (PST) + C: From: Joe Mooch <mooch@OWaTaGu.siam.EDU> + C: Subject: Re: afternoon meeting + C: To: foobar@blt.example.com + C: Message-Id: <a0434793874930@OWaTaGu.siam.EDU> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: 3:30 is fine with me. + C: + S: A003 OK [APPENDUID 1022843275 77712,77713] completed + +4.2.3. Replaying Local Flag Changes + + The disconnected client uses the STORE command to synchronize local + flag state with the server. The disconnected client SHOULD use + +FLAGS.SILENT or -FLAGS.SILENT in order to set or unset flags + modified by the user while offline. The FLAGS form MUST NOT be used, + as there is a risk that this will overwrite flags on the server that + have been changed by some other client. + + Example 4: + + For the message with UID 15, the disconnected client stores the + following flags \Seen and $Highest. The flags were modified on the + server by some other client: \Seen, \Answered, and $Highest. While + + + +Melnikov Informational [Page 14] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + offline, the user requested that the $Highest flags be removed and + that the \Deleted flag be added. The flag synchronization sequence + for the message should look like: + + C: A001 UID STORE 15 +FLAGS.SILENT (\Deleted) + S: A001 STORE completed + C: A002 UID STORE 15 -FLAGS.SILENT ($Highest) + S: A002 STORE completed + + If the disconnected client is able to store an additional binary + state information (or a piece of information that can take a value + from a predefined set of values) in the local cache of an IMAP + mailbox or in a local mailbox (e.g., message priority), and if the + server supports storing of arbitrary keywords, the client MUST use + keywords to store this state on the server. + + Example 5: + + Imagine a speculative mail client that can mark a message as one of + work-related ($Work), personal ($Personal), or spam ($Spam). In + order to mark a message as personal, the client issues: + + C: A001 UID STORE 15 +FLAGS.SILENT ($Personal) + S: A001 STORE completed + C: A002 UID STORE 15 -FLAGS.SILENT ($Work $Spam) + S: A002 STORE completed + + In order to mark the message as not work, not personal and not spam, + the client issues: + + C: A003 UID STORE 15 -FLAGS.SILENT ($Personal $Work $Spam) + S: A003 STORE completed + +4.2.4. Processing Mailbox Compression (EXPUNGE) Requests + + A naive disconnected client implementation that supports compressing + a mailbox while offline may decide to issue an EXPUNGE command to the + server in order to expunge messages marked \Deleted. The problem + with this command during synchronization is that it permanently + erases all messages with the \Deleted flag set, i.e., even those + messages that were marked as \Deleted on the server while the user + was offline. Doing this might result in an unpleasant surprise for + the user. + + Fortunately the [UIDPLUS] extension can help in this case as well. + The extension introduces UID EXPUNGE command, that, unlike EXPUNGE, + takes a UID set parameter, that lists UIDs of all messages that can + be expunged. When processing this command the server erases only + + + +Melnikov Informational [Page 15] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + messages with \Deleted flag listed in the UID list. Thus, messages + not listed in the UID set will not be expunged even if they have the + \Deleted flag set. + + Example 6: + + While the user was offline, 3 messages with UIDs 7, 27, and 65 were + marked \Deleted when the user requested to compress the open mailbox. + Another client marked a message \Deleted on the server (UID 34). + During synchronization, the disconnected client issues: + + C: A001 UID EXPUNGE 7,27,65 + S: * ... EXPUNGE + S: * ... EXPUNGE + S: * ... EXPUNGE + S: A001 UID EXPUNGE completed + + If another client issues UID SEARCH DELETED command (to find all + messages with the \Deleted flag) before and after the UID EXPUNGE, it + will get: + + Before: + + C: B001 UID SEARCH DELETED + S: * SEARCH 65 34 27 7 + S: B001 UID SEARCH completed + + After: + + C: B002 UID SEARCH DELETED + S: * SEARCH 34 + S: B002 UID SEARCH completed + + In the absence of the [UIDPLUS] extension, the following sequence of + commands can be used as an approximation. Note: It's possible for + another client to mark additional messages as deleted while this + sequence is being performed. In this case, these additional messages + will be expunged as well. + + 1) Find all messages marked \Deleted on the server. + + C: A001 UID SEARCH DELETED + S: * SEARCH 65 34 27 7 + S: A001 UID SEARCH completed + + 2) Find all messages that must not be erased (for the previous + example the list will consist of the message with UID 34). + + + + +Melnikov Informational [Page 16] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + 3) Temporarily remove \Deleted flag on all messages found in step 2. + + C: A002 UID STORE 34 -FLAGS.SILENT (\Deleted) + S: A002 UID STORE completed + + 4) Expunge the mailbox. + + C: A003 EXPUNGE + S: * 20 EXPUNGE + S: * 7 EXPUNGE + S: * 1 EXPUNGE + S: A003 EXPUNGE completed + + Here, the message with UID 7 has message number 1, with UID 27 has + message number 7, and with UID 65 has message number 20. + + 5) Restore \Deleted flag on all messages found when performing step + 2. + + C: A004 UID STORE 34 +FLAGS.SILENT (\Deleted) + S: A004 UID STORE completed + +4.2.5. Closing a Mailbox + + When the disconnected client has to close a mailbox, it should not + use the CLOSE command, because CLOSE does a silent EXPUNGE. (Section + 4.2.4 explains why EXPUNGE should not be used by a disconnected + client.) It is safe to use CLOSE only if the mailbox was opened with + EXAMINE. + + If the mailbox was opened with SELECT, the client can use one of the + following commands to implicitly close the mailbox and prevent the + silent expunge: + + 1) UNSELECT - This is a command described in [UNSELECT] that works as + CLOSE, but doesn't cause the silent EXPUNGE. This command is + supported by the server if it reports UNSELECT in its CAPABILITY + list. + + 2) SELECT <another_mailbox> - SELECT causes implicit CLOSE without + EXPUNGE. + + 3) If the client intends to issue LOGOUT after closing the mailbox, + it may just issue LOGOUT, because LOGOUT causes implicit CLOSE + without EXPUNGE as well. + + 4) SELECT <non_existing_mailbox> - If the client knows a mailbox that + doesn't exist or can't be selected, it MAY SELECT it. + + + +Melnikov Informational [Page 17] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + If the client opened the mailbox with SELECT and just wants to avoid + implicit EXPUNGE without closing the mailbox, it may also use the + following: + + 5) EXAMINE <mailbox> - Reselect the same mailbox in read-only mode. + +4.3. Details of "Normal" Synchronization of a Single Mailbox + + The most common form of synchronization is where the human trusts the + integrity of the client's copy of the state of a particular mailbox + and simply wants to bring the client's cache up to date so that it + accurately reflects the mailbox's current state on the server. + +4.3.1. Discovering New Messages and Changes to Old Messages + + Let <lastseenuid> represent the highest UID that the client knows + about in this mailbox. Since UIDs are allocated in strictly + ascending order, this is simply the UID of the last message in the + mailbox that the client knows about. Let <lastseenuid+1> represent + <lastseenuid>'s UID plus one. Let <descriptors> represent a list + consisting of all the FETCH data item items that the implementation + considers part of the descriptor; at a minimum this is just the FLAGS + data item, but it usually also includes BODYSTRUCTURE and + RFC822.SIZE. At this step, <descriptors> SHOULD NOT include RFC822. + + With no further information, the client can issue the following two + commands: + + tag1 UID FETCH <lastseenuid+1>:* <descriptors> + tag2 UID FETCH 1:<lastseenuid> FLAGS + + The first command will request some information about "new" messages + (i.e., messages received by the server since the last + synchronization). It will also allow the client to build a message + number to UID map (only for new messages). The second command allows + the client to + + 1) update cached flags for old messages; + + 2) find out which old messages got expunged; and + + 3) build a mapping between message numbers and UIDs (for old + messages). + + The order here is significant. We want the server to start returning + the list of new message descriptors as fast as it can, so that the + client can start issuing more FETCH commands, so we start out by + asking for the descriptors of all the messages we know the client + + + +Melnikov Informational [Page 18] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + cannot possibly have cached yet. The second command fetches the + information we need to determine what changes may have occurred to + messages that the client already has cached. Note that the former + command should only be issued if the UIDNEXT value cached by the + client differs from the one returned by the server. Once the client + has issued these two commands, there's nothing more the client can do + with this mailbox until the responses to the first command start + arriving. A clever synchronization program might use this time to + fetch its local cache state from disk or to start the process of + synchronizing another mailbox. + + The following is an example of the first FETCH: + + C: A011 UID fetch 131:* (FLAGS BODYSTRUCTURE INTERNALDATE + RFC822.SIZE) + + Note 1: The first FETCH may result in the server's sending a huge + volume of data. A smart disconnected client should use message + ranges (see also Section 3.2.1.2 of [RFC2683]), so that the user is + able to execute a different operation between fetching information + for a group of new messages. + + Example 7: + + Knowing the new UIDNEXT returned by the server on SELECT or EXAMINE + (<uidnext>), the client can split the UID range + <lastseenuid+1>:<uidnext> into groups, e.g., 100 messages. After + that, the client can issue: + + C: A011 UID fetch <lastseenuid+1>:<lastseenuid+100> + (FLAGS BODYSTRUCTURE INTERNALDATE RFC822.SIZE) + ... + C: A012 UID fetch <lastseenuid+101>:<lastseenuid+200> + (FLAGS BODYSTRUCTURE INTERNALDATE RFC822.SIZE) + ... + ... + C: A0FF UID fetch <lastseenuid+901>:<uidnext> + (FLAGS BODYSTRUCTURE INTERNALDATE RFC822.SIZE) + + Note that unless a SEARCH command is issued, it is impossible to + determine how many messages will fall into a subrange, as UIDs are + not necessarily contiguous. + + Note 2: The client SHOULD ignore any unsolicited EXPUNGE responses + received during the first FETCH command. EXPUNGE responses contain + message numbers that are useless to a client that doesn't have the + message-number-to-UID translation table. + + + + +Melnikov Informational [Page 19] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + The second FETCH command will result in zero or more untagged fetch + responses. Each response will have a corresponding UID FETCH data + item. All messages that didn't have a matching untagged FETCH + response MUST be removed from the local cache. + + For example, if the <lastseenuid> had a value 15000 and the local + cache contained 3 messages with the UIDs 12, 777, and 14999, + respectively, then after receiving the following responses from the + server, the client must remove the message with UID 14999 from its + local cache. + + S: * 1 FETCH (UID 12 FLAGS (\Seen)) + S: * 2 FETCH (UID 777 FLAGS (\Answered \Deleted)) + + Note 3: If the client is not interested in flag changes (i.e., the + client only wants to know which old messages are still on the + server), the second FETCH command can be substituted with: + + tag2 UID SEARCH UID 1:<lastseenuid> + + This command will generate less traffic. However, an implementor + should be aware that in order to build the mapping table from message + numbers to UIDs, the output of the SEARCH command MUST be sorted + first, because there is no requirement for a server to return UIDs in + SEARCH response in any particular order. + +4.3.2. Searching for "Interesting" Messages. + + This step is performed entirely on the client (from the information + received in the step described in 4.3.1), entirely on the server, or + on some combination of both. The decision on what is an + "interesting" message is up to the client software and the human. + One easy criterion that should probably be implemented in any client + is whether the message is "too big" for automatic retrieval, where + "too big" is a parameter defined in the client's configuration. + + Another commonly used criterion is the age of a message. For + example, the client may choose to download only messages received in + the last week (in this case, <date> would be today's date minus 7 + days): + + tag3 UID SEARCH UID <uidset> SINCE <date> + + Keep in mind that a date search disregards time and time zone. The + client can avoid doing this search if it specified INTERNALDATE in + <descriptors> on the step described in 4.3.1. If the client did, it + can perform the local search on its message cache. + + + + +Melnikov Informational [Page 20] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + At this step, the client also decides what kind of information about + a particular message to fetch from the server. In particular, even + for a message that is considered "too big", the client MAY choose to + fetch some part(s) of it. For example, if the message is a + multipart/mixed containing a text part and a MPEG attachment, there + is no reason for the client not to fetch the text part. The decision + of which part should or should not be fetched can be based on the + information received in the BODYSTRUCTURE FETCH response data item + (i.e., if BODYSTRUCTURE was included in <descriptors> on the step + described in 4.3.1). + +4.3.3. Populating Cache with "Interesting" Messages. + + Once the client has found out which messages are "interesting", it + can start issuing appropriate FETCH commands for "interesting" + messages or parts thereof. + + Note that fetching a message into the disconnected client's local + cache does NOT imply that the human has (or even will) read the + message. Thus, the synchronization program for a disconnected client + should always be careful to use the .PEEK variants of the FETCH data + items that implicitly set the \Seen flag. + + Once the last descriptor has arrived and the last FETCH command has + been issued, the client simply needs to process the incoming fetch + items and use them to update the local message cache. + + In order to avoid deadlock problems, the client must give processing + of received messages priority over issuing new FETCH commands during + this synchronization process. This may necessitate temporary local + queuing of FETCH requests that cannot be issued without causing a + deadlock. In order to achieve the best use of the "expensive" + network connection, the client will almost certainly need to pay + careful attention to any flow-control information that it can obtain + from the underlying transport connection (usually a TCP connection). + + Note: The requirement stated in the previous paragraph might result + in an unpleasant user experience, if followed blindly. For example, + the user might be unwilling to wait for the client to finish + synchronization before starting to process the user's requests. A + smart disconnected client should allow the user to perform requested + operations in between IMAP commands that are part of the + synchronization process. See also Note 1 in Section 4.3.1. + + + + + + + + +Melnikov Informational [Page 21] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + Example 8: + + After fetching a message BODYSTRUCTURE, the client discovers a + complex MIME message. Then, it decides to fetch MIME headers of the + nested MIME messages and some body parts. + + C: A011 UID fetch 11 (BODYSTRUCTURE) + S: ... + C: A012 UID fetch 11 (BODY[HEADER] BODY[1.MIME] BODY[1.1.MIME] + BODY[1.2.MIME] BODY[2.MIME] BODY[3.MIME] BODY[4.MIME] + BODY[5.MIME] BODY[6.MIME] BODY[7.MIME] BODY[8.MIME] BODY[9.MIME] + BODY[10.MIME] BODY[11.MIME] BODY[12.MIME] BODY[13.MIME] + BODY[14.MIME] BODY[15.MIME] BODY[16.MIME] BODY[17.MIME] + BODY[18.MIME] BODY[19.MIME] BODY[20.MIME] BODY[21.MIME]) + S: ... + C: A013 UID fetch 11 (BODY[1.1] BODY[1.2]) + S: ... + C: A014 UID fetch 11 (BODY[3] BODY[4] BODY[5] BODY[6] BODY[7] BODY[8] + BODY[9] BODY[10] BODY[11] BODY[13] BODY[14] BODY[15] BODY[16] + BODY[21]) + S: ... + +4.3.4. User-Initiated Synchronization + + After the client has finished the main synchronization process as + described in Sections 4.3.1-4.3.3, the user may optionally request + additional synchronization steps while the client is still online. + This is not any different from the process described in Sections + 4.3.2 and 4.3.3. + + Typical examples are: + + 1) fetch all messages selected in UI. + 2) fetch all messages marked as \Flagged on the server. + +4.4. Special Case: Descriptor-Only Synchronization + + For some mailboxes, fetching the descriptors might be the entire + synchronization step. Practical experience with IMAP has shown that + a certain class of mailboxes (e.g., "archival" mailboxes) are used + primarily for long-term storage of important messages that the human + wants to have instantly available on demand but does not want + cluttering up the disconnected client's cache at any other time. + Messages in this kind of mailbox would be fetched exclusively by + explicit actions queued by the local MUA. Thus, the only + synchronization desirable on this kind of mailbox is fetching enough + descriptor information for the user to be able to identify messages + for subsequent download. + + + +Melnikov Informational [Page 22] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + Special mailboxes that receive messages from a high volume, low + priority mailing list might also be in this category, at least when + the human is in a hurry. + +4.5. Special Case: Fast New-Only Synchronization + + In some cases, the human might be in such a hurry that he or she + doesn't care about changes to old messages, just about new messages. + In this case, the client can skip the UID FETCH command that obtains + the flags and UIDs for old messages (1:<lastseenuid>). + +4.6. Special Case: Blind FETCH + + In some cases, the human may know (for whatever reason) that he or + she always wants to fetch any new messages in a particular mailbox, + unconditionally. In this case, the client can just fetch the + messages themselves, rather than just the descriptors, by using a + command like: + + tag1 UID FETCH <lastseenuid+1>:* (FLAGS BODY.PEEK[]) + + Note that this example ignores the fact that the messages can be + arbitrary long. The disconnected client MUST always check for + message size before downloading, unless explicitly told otherwise. A + well-behaved client should instead use something like the following: + + 1) Issue "tag1 UID FETCH <lastseenuid+1>:* (FLAGS RFC822.SIZE)". + + 2) From the message sizes returned in step 1, construct UID set + <required_messages>. + + 3) Issue "tag2 UID FETCH <required_messages> (BODY.PEEK[])". + + or + + 1) Issue "tag1 UID FETCH <lastseenuid+1>:* (FLAGS)". + + 2) Construct UID set <old_uids> from the responses of step 1. + + 3) Issue "tag2 SEARCH UID <old_uids> SMALLER <message_limit>". + Construct UID set <required_messages> from the result of the + SEARCH command. + + 4) Issue "tag3 UID FETCH <required_messages> (BODY.PEEK[])". + + + + + + + +Melnikov Informational [Page 23] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + or + + 1) Issue "tag1 UID FETCH <lastseenuid+1>:* (FLAGS + BODY.PEEK[]<0.<length>>)", where <length> should be replaced with + the maximal message size the client is willing to download. + + Note: In response to such a command, the server will only return + partial data if the message is longer than <length>. It will + return the full message data for any message whose size is smaller + than or equal to <length>. In the former case, the client will + not be able to extract the full MIME structure of the message from + the truncated data, so the client should include BODYSTRUCTURE in + the UID FETCH command as well. + +5. Implementation Considerations + + Below are listed some common implementation pitfalls that should be + considered when implementing a disconnected client. + + 1) Implementing fake UIDs on the client. + + A message scheduled to be uploaded has no UID, as UIDs are + selected by the server. The client may implement fake UIDs + internally in order to reference not-yet-uploaded messages in + further operations. (For example, a message could be scheduled to + be uploaded, but subsequently marked as deleted or copied to + another mailbox). Here, the client MUST NOT under any + circumstances send these fake UIDs to the server. Also, client + implementers should be reminded that according to [IMAP4] a UID is + a 32-bit unsigned integer excluding 0. So, both 4294967295 and + 2147483648 are valid UIDs, and 0 and -1 are both invalid. Some + disconnected mail clients have been known to send negative numbers + (e.g., "-1") as message UIDs to servers during synchronization. + + Situation 1: The user starts composing a new message, edits it, + saves it, continues to edit it, and saves it again. + + A disconnected client may record in its replay log (log of + operations to be replayed on the server during synchronization) + the sequence of operations as shown below. For the purpose of + this situation, we assume that all draft messages are stored in + the mailbox called Drafts on an IMAP server. We will also use the + following conventions: <old_uid> is the UID of the intermediate + version of the draft when it was saved for the first time. This + is a fake UID generated on the client. <new_uid> is the UID of + the final version of the draft. This is another fake UID + generated on the client. + + + + +Melnikov Informational [Page 24] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + 1) APPEND Drafts (\Seen $MDNSent \Drafts) {<nnn>} + ...first version of the message follows... + + 2) APPEND Drafts (\Seen $MDNSent \Drafts) {<mmm>} + ...final version of the message follows... + + 3) STORE <old_uid> +FLAGS (\Deleted) + + Step 1 corresponds to the first attempt to save the draft message, + step 2 corresponds to the second attempt to save the draft + message, and step 3 deletes the first version of the draft message + saved in step 1. + + A naive disconnected client may send the command in step 3 without + replacing the fake client generated <old_uid> with the value + returned by the server in step 1. A server will probably reject + this command, which will make the client believe that the + synchronization sequence has failed. + + 2) Section 5.1 discusses common implementation errors related to + error recovery during playback. + + 3) Don't assume that the disconnected client is the only client used + by the user. + + Situation 2: Some clients may use the \Deleted flag as an + indicator that the message should not appear in the user's view. + Usage of the \Deleted flag for this purpose is not safe, as other + clients (e.g., online clients) might EXPUNGE the mailbox at any + time. + + 4) Beware of data dependencies between synchronization operations. + + It might be very tempting for a client writer to perform some + optimizations on the playback log. Such optimizations might + include removing redundant operations (for example, see + optimization 2 in Section 5.3), or their reordering. + + It is not always safe to reorder or remove redundant operations + during synchronization because some operations may have + dependencies (as Situation 3 demonstrates). So, if in doubt, + don't do this. + + Situation 3: The user copies a message out of a mailbox and then + deletes the mailbox. + + + + + + +Melnikov Informational [Page 25] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + C: A001 SELECT Old-Mail + S: ... + C: A002 UID COPY 111 ToDo + S: A002 OK [COPYUID 1022843345 111 94] Copy completed + ... + C: A015 CLOSE + S: A015 OK Completed + C: A016 DELETE Old-Mail + S: A016 OK Mailbox deletion completed successfully + + If the client performs DELETE (tag A016) first and COPY (tag A002) + second, then the COPY fails. Also, the message that the user so + carefully copied into another mailbox has been lost. + +5.1. Error Recovery during Playback + + Error recovery during synchronization is one of the trickiest parts + to get right. Below, we will discuss certain error conditions and + suggest possible choices for handling them. + + 1) Lost connection to the server. + + The client MUST remember the current position in the playback + (replay) log and replay it starting from the interrupted operation + (the last command issued by the client, but not acknowledged by + the server) the next time it successfully connects to the same + server. If the connection was lost while executing a non- + idempotent IMAP command (see the definition in Section 1), then + when the client is reconnected, it MUST make sure that the + interrupted command was indeed not executed. If it wasn't + executed, the client must restart playback from the interrupted + command, otherwise from the following command. + + Upon reconnect, care must be taken in order to properly reapply + logical operations that are represented by multiple IMAP commands, + e.g., UID EXPUNGE emulation when UID EXPUNGE is not supported by + the server (see Section 4.2.4). + + Once the client detects that the connection to the server was + lost, it MUST stop replaying its log. There are existing + disconnected clients that, to the great annoyance of users, pop up + an error dialog for each and every playback operation that fails. + + 2) Copying/appending messages to a mailbox that doesn't exist. (The + server advertises this condition by sending the TRYCREATE response + code in the tagged NO response to the APPEND or COPY command.) + + + + + +Melnikov Informational [Page 26] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + The user should be advised about the situation and be given one of + the following choices: + + a) Try to recreate a mailbox. + b) Copy/upload messages to another mailbox. + c) Skip copy/upload. + d) Abort replay. + + 3) Copying messages from a mailbox that doesn't exist, or renaming or + getting/changing ACLs [ACL] on a mailbox that doesn't exist: + + a) Skip operation. + b) Abort replay. + + 4) Deleting mailboxes or deleting/expunging messages that no longer + exist. + + This is actually is not an error and should be ignored by the + client. + + 5) Performing operations on messages that no longer exist. + + a) Skip operation. + b) Abort replay. + + In the case of changing flags on an expunged message, the client + should silently ignore the error. + + Note 1: Several synchronization operations map to multiple IMAP + commands (for example, "move" described in 4.2.2). The client must + guarantee atomicity of each such multistep operation. For example, + when performing a "move" between two mailboxes on the same server, if + the server is unable to copy messages, the client MUST NOT attempt to + set the \Deleted flag on the messages being copied, let alone expunge + them. However, the client MAY consider that move operation to have + succeeded even if the server was unable to set the \Deleted flag on + copied messages. + + Note 2: Many synchronization operations have data dependencies. A + failed operation must cause all dependent operations to fail as well. + The client should check this and MUST NOT try to perform all + dependent operations blindly (unless the user corrected the original + problem). For example, a message may be scheduled to be appended to + a mailbox on the server and later on the appended message may be + copied to another mailbox. If the APPEND operation fails, the client + must not attempt to COPY the failed message later on. (See also + Section 5, Situation 3). + + + + +Melnikov Informational [Page 27] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + +5.2. Quality of Implementation Issues + + Below, some quality of implementation issues are listed for + disconnected clients. They will help to write a disconnected client + that works correctly, performs synchronization as quickly as possible + (and thus can make the user happier as well as save her some money), + and minimizes the server load: + + 1) Don't lose information. + + No matter how smart your client is in other areas, if it loses + information, users will get very upset. + + 2) Don't do work unless explicitly asked. Be flexible. Ask all + questions BEFORE starting synchronization, if possible. + + 3) Minimize traffic. + + The client MUST NOT issue a command if the client already received + the required information from the server. + + The client MUST make use of UIDPLUS extension if it is supported + by the server. + + See also optimization 1 in Section 5.3. + + 4) Minimize the number of round-trips. + + Round-trips kill performance, especially on links with high + latency. Sections 4.2.2.5 and 5.2 give some advice on how to + minimize the number of round-trips. + + See also optimization 1 in Section 5.3. + +5.3. Optimizations + + Some useful optimizations are described in this section. A + disconnected client that supports the recommendations listed below + will give the user a more pleasant experience. + + 1) The initial OK or PREAUTH responses may contain the CAPABILITY + response code as described in Section 7.1 of [IMAP4]. This + response code gives the same information as returned by the + CAPABILITY command*. A disconnected client that pays attention to + this response code can avoid sending CAPABILITY command and will + save a round-trip. + + + + + +Melnikov Informational [Page 28] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + * Note: Some servers report in the CAPABILITY response code + extensions that are only relevant in unauthenticated state or in + all states. Such servers usually send another CAPABILITY + response code upon successful authentication using LOGIN or + AUTHENTICATE command (that negotiates no security layer; see + Section 6.2.2 of [IMAP4]). The CAPABILITY response code sent + upon successful LOGIN/AUTHENTICATE might be different from the + CAPABILITY response code in the initial OK response, as + extensions only relevant for unauthenticated state will not be + advertised, and some additional extensions available only in + authenticated and/or selected state will be. + + Example 9: + + S: * OK [CAPABILITY IMAP4REV1 LOGIN-REFERRALS STARTTLS + AUTH=DIGEST-MD5 AUTH=SRP] imap.example.com ready + C: 2 authenticate DIGEST-MD5 + S: 2 OK [CAPABILITY IMAP4REV1 IDLE NAMESPACE MAILBOX-REFERRALS SCAN + SORT THREAD=REFERENCES THREAD=ORDEREDSUBJECT MULTIAPPEND] + User authenticated (no layer) + + 2) An advanced disconnected client may choose to optimize its replay + log. For example, there might be some operations that are + redundant (the list is not complete): + + a) an EXPUNGE followed by another EXPUNGE or CLOSE; + b) changing flags (other than the \Deleted flag) on a message that + gets immediately expunged; + c) opening and closing the same mailbox. + + When optimizing, be careful about data dependencies between commands. + For example, if the client is wishing to optimize (see case b, above) + + tag1 UID STORE <uid1> +FLAGS (\Deleted) + ... + tag2 UID STORE <uid1> +FLAGS (\Flagged) + ... + tag3 UID COPY <uid1> "Backup" + ... + tag4 UID EXPUNGE <uid1> + + it can't remove the second UID STORE command because the message is + being copied before it gets expunged. + + In general, it might be a good idea to keep mailboxes open during + synchronization (see case c above), if possible. This can be more + easily achieved in conjunction with optimization 3 described below. + + + + +Melnikov Informational [Page 29] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + 3) Perform some synchronization steps in parallel, if possible. + + Several synchronization steps don't depend on each other and thus + can be performed in parallel. Because the server machine is + usually more powerful than the client machine and can perform some + operations in parallel, this may speed up the total time of + synchronization. + + In order to achieve such parallelization, the client will have to + open more than one connection to the same server. Client writers + should not forget about non-trivial cost associated with + establishing a TCP connection and performing an authentication. + The disconnected client MUST NOT use one connection per mailbox. + In most cases, it is sufficient to have two connections. The + disconnected client SHOULD avoid selecting the same mailbox in + more than one connection; see Section 3.1.1 of [RFC2683] for more + details. + + Any mailbox synchronization MUST start with checking the + UIDVALIDITY as described in Section 4.1 of this document. The + client MAY use STATUS command to check UID Validity of a non- + selected mailbox. This is preferable to opening many connections + to the same server to perform synchronization of multiple + mailboxes simultaneously. As described in Section 5.3.10 of + [IMAP4], this SHOULD NOT be used on the selected mailbox. + +6. IMAP Extensions That May Help + + The following extensions can save traffic and/or the number of + round-trips: + + 1) The use of [UIDPLUS] is discussed in Sections 4.1, 4.2.1, 4.2.2.1 + and 4.2.4. + + 2) The use of the MULTIAPPEND and LITERAL+ extensions for uploading + messages is discussed in Section 4.2.2.5. + + 3) Use the CONDSTORE extension (see Section 6.1) for quick flag + resynchronization. + +6.1. CONDSTORE Extension + + An advanced disconnected mail client should use the [CONDSTORE] + extension when it is supported by the server. The client must cache + the value from HIGHESTMODSEQ OK response code received on mailbox + opening and update it whenever the server sends MODSEQ FETCH data + items. + + + + +Melnikov Informational [Page 30] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + If the client receives NOMODSEQ OK untagged response instead of + HIGHESTMODSEQ, it MUST remove the last known HIGHESTMODSEQ value from + its cache and follow the more general instructions in Section 3. + + When the client opens the mailbox for synchronization, it first + compares UIDVALIDITY as described in step d-1 in Section 3. If the + cached UIDVALIDITY value matches the one returned by the server, the + client MUST compare the cached value of HIGHESTMODSEQ with the one + returned by the server. If the cached HIGHESTMODSEQ value also + matches the one returned by the server, then the client MUST NOT + fetch flags for cached messages, as they hasn't changed. If the + value on the server is higher than the cached one, the client MAY use + "SEARCH MODSEQ <cached-value>" to find all messages with flags + changed since the last time the client was online and had the mailbox + opened. Alternatively, the client MAY use "FETCH 1:* (FLAGS) + (CHANGEDSINCE <cached-value>)". The latter operation combines + searching for changed messages and fetching new information. + + In all cases, the client still needs to fetch information about new + messages (if requested by the user) as well as discover which + messages have been expunged. + + Step d ("Server-to-client synchronization") in Section 4 in the + presence of the CONDSTORE extension is amended as follows: + + d) "Server-to-client synchronization" - For each mailbox that + requires synchronization, do the following: + + 1a) Check the mailbox UIDVALIDITY (see section 4.1 for more + details) with SELECT/EXAMINE/STATUS. + + If the UIDVALIDITY value returned by the server differs, the + client MUST + + * empty the local cache of that mailbox; + * "forget" the cached HIGHESTMODSEQ value for the mailbox; + * remove any pending "actions" that refer to UIDs in that + mailbox (note that this doesn't affect actions performed on + client-generated fake UIDs; see Section 5); and + * skip steps 1b and 2-II; + + 1b) Check the mailbox HIGHESTMODSEQ. If the cached value is the + same as the one returned by the server, skip fetching message + flags on step 2-II, i.e., the client only has to find out + which messages got expunged. + + + + + + +Melnikov Informational [Page 31] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + 2) Fetch the current "descriptors". + + I) Discover new messages. + + II) Discover changes to old messages and flags for new messages + using + "FETCH 1:* (FLAGS) (CHANGEDSINCE <cached-value>)" or + "SEARCH MODSEQ <cached-value>". + + Discover expunged messages; for example, using + "UID SEARCH 1:<lastseenuid>". (All messages not returned + in this command are expunged.) + + 3) Fetch the bodies of any "interesting" messages that the client + doesn't already have. + + Example 10: + + The UIDVALIDITY value is the same, but the HIGHESTMODSEQ value + has changed on the server while the client was offline. + + C: A142 SELECT INBOX + S: * 172 EXISTS + S: * 1 RECENT + S: * OK [UNSEEN 12] Message 12 is first unseen + S: * OK [UIDVALIDITY 3857529045] UIDs valid + S: * OK [UIDNEXT 201] Predicted next UID + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited + S: * OK [HIGHESTMODSEQ 20010715194045007] + S: A142 OK [READ-WRITE] SELECT completed + + After that, either: + + C: A143 UID FETCH 1:* (FLAGS) (CHANGEDSINCE 20010715194032001) + S: * 2 FETCH (UID 6 MODSEQ (20010715205008000) FLAGS (\Deleted)) + S: * 5 FETCH (UID 9 MODSEQ (20010715195517000) FLAGS ($NoJunk + $AutoJunk $MDNSent)) + ... + S: A143 OK FETCH completed + + or: + + + + + + + + + +Melnikov Informational [Page 32] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + + C: A143 UID SEARCH MODSEQ 20010715194032001 UID 1:20 + S: * SEARCH 6 9 11 12 18 19 20 23 (MODSEQ 20010917162500) + S: A143 OK Search complete + C: A144 UID SEARCH 1:20 + S: * SEARCH 6 9 ... + S: A144 OK FETCH completed + +7. Security Considerations + + It is believed that this document does not raise any new security + concerns that are not already present in the base [IMAP4] protocol, + and these issues are discussed in [IMAP4]. Additional security + considerations may be found in different extensions mentioned in this + document; in particular, in [UIDPLUS], [LITERAL+], [CONDSTORE], + [MULTIAPPEND], and [UNSELECT]. + + Implementers are also reminded about the importance of thorough + testing. + +8. References + +8.1. Normative References + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [IMAP4] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - + VERSION 4rev1", RFC 3501, March 2003. + + [UIDPLUS] Crispin, M., "Internet Message Access Protocol (IMAP) - + UIDPLUS extension", RFC 4315, December 2005. + + [LITERAL+] Myers, J., "IMAP4 non-synchronizing literals", RFC + 2088, January 1997. + + [CONDSTORE] Melnikov, A. and S. Hole, "IMAP Extension for + Conditional STORE Operation or Quick Flag Changes + Resynchronization", RFC 4551, June 2006. + + [MULTIAPPEND] Crispin, M., "Internet Message Access Protocol (IMAP) - + MULTIAPPEND Extension", RFC 3502, March 2003. + + [UNSELECT] Melnikov, A., "Internet Message Access Protocol (IMAP) + UNSELECT command", RFC 3691, February 2004. + + [RFC2683] Leiba, B., "IMAP4 Implementation Recommendations", RFC + 2683, September 1999. + + + + +Melnikov Informational [Page 33] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + +8.2. Informative References + + [ACL] Melnikov, A., "IMAP4 Access Control List (ACL) + Extension", RFC 4314, December 2005. + + [IMAP-MODEL] Crispin, M., "Distributed Electronic Mail Models in + IMAP4", RFC 1733, December 1994. + +9. Acknowledgements + + This document is based on version 01 of the text written by Rob + Austein in November 1994. + + The editor appreciates comments posted by Mark Crispin to the IMAP + mailing list and the comments/corrections/ideas received from Grant + Baillie, Cyrus Daboo, John G. Myers, Chris Newman, and Timo Sirainen. + + The editor would also like to thank the developers of Netscape + Messenger and Mozilla mail clients for providing examples of + disconnected mail clients that served as a base for many + recommendations in this document. + +Editor's Address + + Alexey Melnikov + Isode Limited + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex + TW12 2BX + United Kingdom + + Phone: +44 77 53759732 + EMail: alexey.melnikov@isode.com + + + + + + + + + + + + + + + + + +Melnikov Informational [Page 34] + +RFC 4549 Synch Ops for Disconnected IMAP4 Clients June 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + + + +Melnikov Informational [Page 35] + diff --git a/imap/docs/rfc/rfc4551.txt b/imap/docs/rfc/rfc4551.txt new file mode 100644 index 00000000..894b5109 --- /dev/null +++ b/imap/docs/rfc/rfc4551.txt @@ -0,0 +1,1403 @@ + + + + + + +Network Working Group A. Melnikov +Request for Comments: 4551 Isode Ltd. +Updates: 3501 S. Hole +Category: Standards Track ACI WorldWide/MessagingDirect + June 2006 + + + IMAP Extension for Conditional STORE Operation + or Quick Flag Changes Resynchronization + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + Often, multiple IMAP (RFC 3501) clients need to coordinate changes to + a common IMAP mailbox. Examples include different clients working on + behalf of the same user, and multiple users accessing shared + mailboxes. These clients need a mechanism to synchronize state + changes for messages within the mailbox. They must be able to + guarantee that only one client can change message state (e.g., + message flags) at any time. An example of such an application is use + of an IMAP mailbox as a message queue with multiple dequeueing + clients. + + The Conditional Store facility provides a protected update mechanism + for message state information that can detect and resolve conflicts + between multiple writing mail clients. + + The Conditional Store facility also allows a client to quickly + resynchronize mailbox flag changes. + + This document defines an extension to IMAP (RFC 3501). + + + + + + + + + +Melnikov & Hole Standards Track [Page 1] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + +Table of Contents + + 1. Introduction and Overview ................................. 3 + 2. Conventions Used in This Document ......................... 5 + 3. IMAP Protocol Changes ..................................... 6 + 3.1. New OK untagged responses for SELECT and EXAMINE ......... 6 + 3.1.1. HIGHESTMODSEQ response code ............................ 6 + 3.1.2. NOMODSEQ response code ................................. 7 + 3.2. STORE and UID STORE Commands ............................. 7 + 3.3 FETCH and UID FETCH Commands ..............................13 + 3.3.1. CHANGEDSINCE FETCH modifier ............................13 + 3.3.2. MODSEQ message data item in FETCH Command ..............14 + 3.4. MODSEQ search criterion in SEARCH ........................16 + 3.5. Modified SEARCH untagged response ........................17 + 3.6. HIGHESTMODSEQ status data items ..........................17 + 3.7. CONDSTORE parameter to SELECT and EXAMINE ................18 + 3.8. Additional quality of implementation issues ..............18 + 4. Formal Syntax .............................................19 + 5. Server implementation considerations ......................21 + 6. Security Considerations ...................................22 + 7. IANA Considerations .......................................22 + 8. References ................................................23 + 8.1. Normative References .....................................23 + 8.2. Informative References ...................................23 + 9. Acknowledgements ..........................................23 + + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov & Hole Standards Track [Page 2] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + +1. Introduction and Overview + + The Conditional STORE extension is present in any IMAP4 + implementation that returns "CONDSTORE" as one of the supported + capabilities in the CAPABILITY command response. + + An IMAP server that supports this extension MUST associate a positive + unsigned 64-bit value called a modification sequence (mod-sequence) + with every IMAP message. This is an opaque value updated by the + server whenever a metadata item is modified. The server MUST + guarantee that each STORE command performed on the same mailbox + (including simultaneous stores to different metadata items from + different connections) will get a different mod-sequence value. + Also, for any two successful STORE operations performed in the same + session on the same mailbox, the mod-sequence of the second completed + operation MUST be greater than the mod-sequence of the first + completed. Note that the latter rule disallows the use of the system + clock as a mod-sequence, because if system time changes (e.g., an NTP + [NTP] client adjusting the time), the next generated value might be + less than the previous one. + + Mod-sequences allow a client that supports the CONDSTORE extension to + determine if a message metadata has changed since some known moment. + Whenever the state of a flag changes (i.e., the flag is added where + previously it wasn't set, or the flag is removed and before it was + set) the value of the modification sequence for the message MUST be + updated. Adding the flag when it is already present or removing when + it is not present SHOULD NOT change the mod-sequence. + + When a message is appended to a mailbox (via the IMAP APPEND command, + COPY to the mailbox, or using an external mechanism) the server + generates a new modification sequence that is higher than the highest + modification sequence of all messages in the mailbox and assigns it + to the appended message. + + The server MAY store separate (per-message) modification sequence + values for different metadata items. If the server does so, per- + message mod-sequence is the highest mod-sequence of all metadata + items for the specified message. + + The server that supports this extension is not required to be able to + store mod-sequences for every available mailbox. Section 3.1.2 + describes how the server may act if a particular mailbox doesn't + support the persistent storage of mod-sequences. + + + + + + + +Melnikov & Hole Standards Track [Page 3] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + This extension makes the following changes to the IMAP4 protocol: + + a) adds UNCHANGEDSINCE STORE modifier. + + b) adds the MODIFIED response code which should be used with an OK + response to the STORE command. (It can also be used in a NO + response.) + + c) adds a new MODSEQ message data item for use with the FETCH + command. + + d) adds CHANGEDSINCE FETCH modifier. + + e) adds a new MODSEQ search criterion. + + f) extends the syntax of untagged SEARCH responses to include + mod-sequence. + + g) adds new OK untagged responses for the SELECT and EXAMINE + commands. + + h) defines an additional parameter to SELECT/EXAMINE commands. + + i) adds the HIGHESTMODSEQ status data item to the STATUS command. + + A client supporting CONDSTORE extension indicates its willingness to + receive mod-sequence updates in all untagged FETCH responses by + issuing: + + - a SELECT or EXAMINE command with the CONDSTORE parameter, + - a STATUS (HIGHESTMODSEQ) command, + - a FETCH or SEARCH command that includes the MODSEQ message data + item, + - a FETCH command with the CHANGEDSINCE modifier, or + - a STORE command with the UNCHANGEDSINCE modifier. + + The server MUST include mod-sequence data in all subsequent untagged + FETCH responses (until the connection is closed), whether they were + caused by a regular STORE, a STORE with UNCHANGEDSINCE modifier, or + an external agent. + + This document uses the term "CONDSTORE-aware client" to refer to a + client that announces its willingness to receive mod-sequence updates + as described above. The term "CONDSTORE enabling command" will refer + any of the commands listed above. A future extension to this + document may extend the list of CONDSTORE enabling commands. A first + CONDSTORE enabling command executed in the session MUST cause the + + + + +Melnikov & Hole Standards Track [Page 4] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + server to return HIGHESTMODSEQ (Section 3.1.1) unless the server has + sent NOMODSEQ (Section 3.1.2) response code when the currently + selected mailbox was selected. + + The rest of this document describes the protocol changes more + rigorously. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [KEYWORDS]. + + In examples, lines beginning with "S:" are sent by the IMAP server, + and lines beginning with "C:" are sent by the client. Line breaks + may appear in example commands solely for editorial clarity; when + present in the actual message, they are represented by "CRLF". + + Formal syntax is defined using ABNF [ABNF]. + + The term "metadata" or "metadata item" is used throughout this + document. It refers to any system or user-defined keyword. Future + documents may extend "metadata" to include other dynamic message + data. + + Some IMAP mailboxes are private, accessible only to the owning user. + Other mailboxes are not, either because the owner has set an Access + Control List [ACL] that permits access by other users, or because it + is a shared mailbox. Let's call a metadata item "shared" for the + mailbox if any changes to the metadata items are persistent and + visible to all other users accessing the mailbox. Otherwise, the + metadata item is called "private". Note that private metadata items + are still visible to all sessions accessing the mailbox as the same + user. Also note that different mailboxes may have different metadata + items as shared. + + See Section 1 for the definition of a "CONDSTORE-aware client" and a + "CONDSTORE enabling command". + + + + + + + + + + + + + +Melnikov & Hole Standards Track [Page 5] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + +3. IMAP Protocol Changes + +3.1. New OK Untagged Responses for SELECT and EXAMINE + + This document adds two new response codes, HIGHESTMODSEQ and + NOMODSEQ. One of those response codes MUST be returned in the OK + untagged response for a successful SELECT/EXAMINE command. + + When opening a mailbox, the server must check if the mailbox supports + the persistent storage of mod-sequences. If the mailbox supports the + persistent storage of mod-sequences and the mailbox open operation + succeeds, the server MUST send the OK untagged response including + HIGHESTMODSEQ response code. If the persistent storage for the + mailbox is not supported, the server MUST send the OK untagged + response including NOMODSEQ response code instead. + +3.1.1. HIGHESTMODSEQ Response Code + + This document adds a new response code that is returned in the OK + untagged response for the SELECT and EXAMINE commands. A server + supporting the persistent storage of mod-sequences for the mailbox + MUST send the OK untagged response including HIGHESTMODSEQ response + code with every successful SELECT or EXAMINE command: + + OK [HIGHESTMODSEQ <mod-sequence-value>] + + where <mod-sequence-value> is the highest mod-sequence value of + all messages in the mailbox. When the server changes UIDVALIDITY + for a mailbox, it doesn't have to keep the same HIGHESTMODSEQ for + the mailbox. + + A disconnected client can use the value of HIGHESTMODSEQ to check if + it has to refetch metadata from the server. If the UIDVALIDITY value + has changed for the selected mailbox, the client MUST delete the + cached value of HIGHESTMODSEQ. If UIDVALIDITY for the mailbox is the + same, and if the HIGHESTMODSEQ value stored in the client's cache is + less than the value returned by the server, then some metadata items + on the server have changed since the last synchronization, and the + client needs to update its cache. The client MAY use SEARCH MODSEQ + (Section 3.4) to find out exactly which metadata items have changed. + Alternatively, the client MAY issue FETCH with the CHANGEDSINCE + modifier (Section 3.3.1) in order to fetch data for all messages that + have metadata items changed since some known modification sequence. + + Example 1: + + C: A142 SELECT INBOX + S: * 172 EXISTS + + + +Melnikov & Hole Standards Track [Page 6] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + S: * 1 RECENT + S: * OK [UNSEEN 12] Message 12 is first unseen + S: * OK [UIDVALIDITY 3857529045] UIDs valid + S: * OK [UIDNEXT 4392] Predicted next UID + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited + S: * OK [HIGHESTMODSEQ 715194045007] + S: A142 OK [READ-WRITE] SELECT completed + +3.1.2. NOMODSEQ Response Code + + A server that doesn't support the persistent storage of mod-sequences + for the mailbox MUST send the OK untagged response including NOMODSEQ + response code with every successful SELECT or EXAMINE command. A + server that returned NOMODSEQ response code for a mailbox, which + subsequently receives one of the following commands while the mailbox + is selected: + + - a FETCH command with the CHANGEDSINCE modifier, + - a FETCH or SEARCH command that includes the MODSEQ message data + item, or + - a STORE command with the UNCHANGEDSINCE modifier + + MUST reject any such command with the tagged BAD response. + + Example 2: + + C: A142 SELECT INBOX + S: * 172 EXISTS + S: * 1 RECENT + S: * OK [UNSEEN 12] Message 12 is first unseen + S: * OK [UIDVALIDITY 3857529045] UIDs valid + S: * OK [UIDNEXT 4392] Predicted next UID + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited + S: * OK [NOMODSEQ] Sorry, this mailbox format doesn't support + modsequences + S: A142 OK [READ-WRITE] SELECT completed + +3.2. STORE and UID STORE Commands + + This document defines the following STORE modifier (see Section 2.5 + of [IMAPABNF]): + + UNCHANGEDSINCE <mod-sequence> + + For each message specified in the message set, the server performs + the following. If the mod-sequence of any metadata item of the + + + +Melnikov & Hole Standards Track [Page 7] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + message is equal or less than the specified UNCHANGEDSINCE value, + then the requested operation (as described by the message data + item) is performed. If the operation is successful, the server + MUST update the mod-sequence attribute of the message. An + untagged FETCH response MUST be sent, even if the .SILENT suffix + is specified, and the response MUST include the MODSEQ message + data item. This is required to update the client's cache with the + correct mod-sequence values. See Section 3.3.2 for more details. + + However, if the mod-sequence of any metadata item of the message + is greater than the specified UNCHANGEDSINCE value, then the + requested operation MUST NOT be performed. In this case, the + mod-sequence attribute of the message is not updated, and the + message number (or unique identifier in the case of the UID STORE + command) is added to the list of messages that failed the + UNCHANGESINCE test. + + When the server finished performing the operation on all the + messages in the message set, it checks for a non-empty list of + messages that failed the UNCHANGESINCE test. If this list is + non-empty, the server MUST return in the tagged response a + MODIFIED response code. The MODIFIED response code includes the + message set (for STORE) or set of UIDs (for UID STORE) of all + messages that failed the UNCHANGESINCE test. + + Example 3: + + All messages pass the UNCHANGESINCE test. + + C: a103 UID STORE 6,4,8 (UNCHANGEDSINCE 12121230045) + +FLAGS.SILENT (\Deleted) + S: * 1 FETCH (UID 4 MODSEQ (12121231000)) + S: * 2 FETCH (UID 6 MODSEQ (12121230852)) + S: * 4 FETCH (UID 8 MODSEQ (12121130956)) + S: a103 OK Conditional Store completed + + Example 4: + + C: a104 STORE * (UNCHANGEDSINCE 12121230045) +FLAGS.SILENT + (\Deleted $Processed) + S: * 50 FETCH (MODSEQ (12111230047)) + S: a104 OK Store (conditional) completed + + Example 5: + + C: c101 STORE 1 (UNCHANGEDSINCE 12121230045) -FLAGS.SILENT + (\Deleted) + S: * OK [HIGHESTMODSEQ 12111230047] + + + +Melnikov & Hole Standards Track [Page 8] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + S: * 50 FETCH (MODSEQ (12111230048)) + S: c101 OK Store (conditional) completed + + HIGHESTMODSEQ response code was sent by the server presumably + because this was the first CONDSTORE enabling command. + + Example 6: + + In spite of the failure of the conditional STORE operation for + message 7, the server continues to process the conditional STORE + in order to find all messages that fail the test. + + C: d105 STORE 7,5,9 (UNCHANGEDSINCE 320162338) + +FLAGS.SILENT (\Deleted) + S: * 5 FETCH (MODSEQ (320162350)) + S: d105 OK [MODIFIED 7,9] Conditional STORE failed + + Example 7: + + Same as above, but the server follows the SHOULD recommendation in + Section 6.4.6 of [IMAP4]. + + C: d105 STORE 7,5,9 (UNCHANGEDSINCE 320162338) + +FLAGS.SILENT (\Deleted) + S: * 7 FETCH (MODSEQ (320162342) FLAGS (\Seen \Deleted)) + S: * 5 FETCH (MODSEQ (320162350)) + S: * 9 FETCH (MODSEQ (320162349) FLAGS (\Answered)) + S: d105 OK [MODIFIED 7,9] Conditional STORE failed + + Use of UNCHANGEDSINCE with a modification sequence of 0 always + fails if the metadata item exists. A system flag MUST always be + considered existent, whether it was set or not. + + Example 8: + + C: a102 STORE 12 (UNCHANGEDSINCE 0) + +FLAGS.SILENT ($MDNSent) + S: a102 OK [MODIFIED 12] Conditional STORE failed + + The client has tested the presence of the $MDNSent user-defined + keyword. + + Note: A client trying to make an atomic change to the state of a + particular metadata item (or a set of metadata items) should be + prepared to deal with the case when the server returns the MODIFIED + response code if the state of the metadata item being watched hasn't + changed (but the state of some other metadata item has). This is + necessary, because some servers don't store separate mod-sequences + + + +Melnikov & Hole Standards Track [Page 9] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + for different metadata items. However, a server implementation + SHOULD avoid generating spurious MODIFIED responses for +FLAGS/-FLAGS + STORE operations, even when the server stores a single mod-sequence + per message. Section 5 describes how this can be achieved. + + Unless the server has included an unsolicited FETCH to update + client's knowledge about messages that have failed the UNCHANGEDSINCE + test, upon receipt of the MODIFIED response code, the client SHOULD + try to figure out if the required metadata items have indeed changed + by issuing FETCH or NOOP command. It is RECOMMENDED that the server + avoids the need for the client to do that by sending an unsolicited + FETCH response (Examples 9 and 10). + + If the required metadata items haven't changed, the client SHOULD + retry the command with the new mod-sequence. The client SHOULD allow + for a configurable but reasonable number of retries (at least 2). + + Example 9: + + In the example below, the server returns the MODIFIED response + code without sending information describing why the STORE + UNCHANGEDSINCE operation has failed. + + C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) + +FLAGS.SILENT ($Processed) + S: * 100 FETCH (MODSEQ (303181230852)) + S: * 102 FETCH (MODSEQ (303181230852)) + ... + S: * 150 FETCH (MODSEQ (303181230852)) + S: a106 OK [MODIFIED 101] Conditional STORE failed + + The flag $Processed was set on the message 101... + + C: a107 NOOP + S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed)) + S: a107 OK + + Or the flag hasn't changed, but another has (note that this server + behaviour is discouraged. Server implementers should also see + Section 5)... + + C: b107 NOOP + S: * 101 FETCH (MODSEQ (303011130956) FLAGS (\Deleted \Answered)) + S: b107 OK + + ...and the client retries the operation for the message 101 with + the updated UNCHANGEDSINCE value + + + + +Melnikov & Hole Standards Track [Page 10] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + C: b108 STORE 101 (UNCHANGEDSINCE 303011130956) + +FLAGS.SILENT ($Processed) + S: * 101 FETCH (MODSEQ (303181230852)) + S: b108 OK Conditional Store completed + + Example 10: + + Same as above, but the server avoids the need for the client to + poll for changes. + + The flag $Processed was set on the message 101 by another + client... + + C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) + +FLAGS.SILENT ($Processed) + S: * 100 FETCH (MODSEQ (303181230852)) + S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed)) + S: * 102 FETCH (MODSEQ (303181230852)) + ... + S: * 150 FETCH (MODSEQ (303181230852)) + S: a106 OK [MODIFIED 101] Conditional STORE failed + + Or the flag hasn't changed, but another has (note that this server + behaviour is discouraged. Server implementers should also see + Section 5)... + + C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) + +FLAGS.SILENT ($Processed) + S: * 100 FETCH (MODSEQ (303181230852)) + S: * 101 FETCH (MODSEQ (303011130956) FLAGS (\Deleted \Answered)) + S: * 102 FETCH (MODSEQ (303181230852)) + ... + S: * 150 FETCH (MODSEQ (303181230852)) + S: a106 OK [MODIFIED 101] Conditional STORE failed + + ...and the client retries the operation for the message 101 with + the updated UNCHANGEDSINCE value + + C: b108 STORE 101 (UNCHANGEDSINCE 303011130956) + +FLAGS.SILENT ($Processed) + S: * 101 FETCH (MODSEQ (303181230852)) + S: b108 OK Conditional Store completed + + Or the flag hasn't changed, but another has (nice server + behaviour. Server implementers should also see Section 5)... + + C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) + +FLAGS.SILENT ($Processed) + + + +Melnikov & Hole Standards Track [Page 11] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + S: * 100 FETCH (MODSEQ (303181230852)) + S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed \Deleted + \Answered)) + S: * 102 FETCH (MODSEQ (303181230852)) + ... + S: * 150 FETCH (MODSEQ (303181230852)) + S: a106 OK Conditional STORE completed + + Example 11: + + The following example is based on the example from the Section + 4.2.3 of [RFC-2180] and demonstrates that the MODIFIED response + code may be also returned in the tagged NO response. + + Client tries to conditionally STORE flags on a mixture of expunged + and non-expunged messages; one message fails the UNCHANGEDSINCE + test. + + C: B001 STORE 1:7 (UNCHANGEDSINCE 320172338) +FLAGS (\SEEN) + S: * 1 FETCH (MODSEQ (320172342) FLAGS (\SEEN)) + S: * 3 FETCH (MODSEQ (320172342) FLAGS (\SEEN)) + S: B001 NO [MODIFIED 2] Some of the messages no longer exist. + + C: B002 NOOP + S: * 4 EXPUNGE + S: * 4 EXPUNGE + S: * 4 EXPUNGE + S: * 4 EXPUNGE + S: * 2 FETCH (MODSEQ (320172340) FLAGS (\Deleted \Answered)) + S: B002 OK NOOP Completed. + + By receiving FETCH responses for messages 1 and 3, and EXPUNGE + responses that indicate that messages 4 through 7 have been + expunged, the client retries the operation only for the message 2. + The updated UNCHANGEDSINCE value is used. + + C: b003 STORE 2 (UNCHANGEDSINCE 320172340) +FLAGS (\Seen) + S: * 2 FETCH (MODSEQ (320180050)) + S: b003 OK Conditional Store completed + + Note: If a message is specified multiple times in the message set, + and the server doesn't internally eliminate duplicates from the + message set, it MUST NOT fail the conditional STORE operation for the + second (or subsequent) occurrence of the message if the operation + completed successfully for the first occurrence. For example, if the + client specifies: + + + + + +Melnikov & Hole Standards Track [Page 12] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + e105 STORE 7,3:9 (UNCHANGEDSINCE 12121230045) + +FLAGS.SILENT (\Deleted) + + the server must not fail the operation for message 7 as part of + processing "3:9" if it succeeded when message 7 was processed the + first time. + + Once the client specified the UNCHANGEDSINCE modifier in a STORE + command, the server MUST include the MODSEQ fetch response data items + in all subsequent unsolicited FETCH responses. + + This document also changes the behaviour of the server when it has + performed a STORE or UID STORE command and the UNCHANGEDSINCE + modifier is not specified. If the operation is successful for a + message, the server MUST update the mod-sequence attribute of the + message. The server is REQUIRED to include the mod-sequence value + whenever it decides to send the unsolicited FETCH response to all + CONDSTORE-aware clients that have opened the mailbox containing the + message. + + Server implementers should also see Section 3.8 for additional + quality of implementation issues related to the STORE command. + +3.3. FETCH and UID FETCH Commands + +3.3.1. CHANGEDSINCE FETCH Modifier + + This document defines the following FETCH modifier (see Section 2.4 + of [IMAPABNF]): + + CHANGEDSINCE <mod-sequence> + + CHANGEDSINCE FETCH modifier allows to create a further subset of + the list of messages described by sequence set. The information + described by message data items is only returned for messages that + have mod-sequence bigger than <mod-sequence>. + + When CHANGEDSINCE FETCH modifier is specified, it implicitly adds + MODSEQ FETCH message data item (Section 3.3.2). + + Example 12: + + C: s100 UID FETCH 1:* (FLAGS) (CHANGEDSINCE 12345) + S: * 1 FETCH (UID 4 MODSEQ (65402) FLAGS (\Seen)) + S: * 2 FETCH (UID 6 MODSEQ (75403) FLAGS (\Deleted)) + S: * 4 FETCH (UID 8 MODSEQ (29738) FLAGS ($NoJunk $AutoJunk + $MDNSent)) + S: s100 OK FETCH completed + + + +Melnikov & Hole Standards Track [Page 13] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + +3.3.2. MODSEQ Message Data Item in FETCH Command + + This extension adds a MODSEQ message data item to the FETCH command. + The MODSEQ message data item allows clients to retrieve mod-sequence + values for a range of messages in the currently selected mailbox. + + Once the client specified the MODSEQ message data item in a FETCH + request, the server MUST include the MODSEQ fetch response data items + in all subsequent unsolicited FETCH responses. + + Syntax: MODSEQ + + The MODSEQ message data item causes the server to return MODSEQ + fetch response data items. + + Syntax: MODSEQ ( <permsg-modsequence> ) + + MODSEQ response data items contain per-message mod-sequences. + + The MODSEQ response data item is returned if the client issued + FETCH with MODSEQ message data item. It also allows the server to + notify the client about mod-sequence changes caused by conditional + STOREs (Section 3.2) and/or changes caused by external sources. + + Example 13: + + C: a FETCH 1:3 (MODSEQ) + S: * 1 FETCH (MODSEQ (624140003)) + S: * 2 FETCH (MODSEQ (624140007)) + S: * 3 FETCH (MODSEQ (624140005)) + S: a OK Fetch complete + + In this example, the client requests per-message mod-sequences for + a set of messages. + + When a flag for a message is modified in a different session, the + server sends an unsolicited FETCH response containing the mod- + sequence for the message. + + Example 14: + + (Session 1, authenticated as a user "alex"). The user adds a + shared flag \Deleted: + + C: A142 SELECT INBOX + ... + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS (\Answered \Deleted \Seen \*)] Limited + + + +Melnikov & Hole Standards Track [Page 14] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + ... + + C: A160 STORE 7 +FLAGS.SILENT (\Deleted) + S: * 7 FETCH (MODSEQ (2121231000)) + S: A160 OK Store completed + + (Session 2, also authenticated as the user "alex"). Any changes + to flags are always reported to all sessions authenticated as the + same user as in the session 1. + + C: C180 NOOP + S: * 7 FETCH (FLAGS (\Deleted \Answered) MODSEQ (12121231000)) + S: C180 OK Noop completed + + (Session 3, authenticated as a user "andrew"). As \Deleted is a + shared flag, changes in session 1 are also reported in session 3: + + C: D210 NOOP + S: * 7 FETCH (FLAGS (\Deleted \Answered) MODSEQ (12121231000)) + S: D210 OK Noop completed + + The user modifies a private flag \Seen in session 1... + + C: A240 STORE 7 +FLAGS.SILENT (\Seen) + S: * 7 FETCH (MODSEQ (12121231777)) + S: A240 OK Store completed + + ...which is only reported in session 2... + + C: C270 NOOP + S: * 7 FETCH (FLAGS (\Deleted \Answered \Seen) MODSEQ + (12121231777)) + S: C270 OK Noop completed + + ...but not in session 3. + + C: D300 NOOP + S: D300 OK Noop completed + + And finally, the user removes flags \Answered (shared) and \Seen + (private) in session 1. + + C: A330 STORE 7 -FLAGS.SILENT (\Answered \Seen) + S: * 7 FETCH (MODSEQ (12121245160)) + S: A330 OK Store completed + + + + + + +Melnikov & Hole Standards Track [Page 15] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + Both changes are reported in the session 2... + + C: C360 NOOP + S: * 7 FETCH (FLAGS (\Deleted) MODSEQ (12121245160)) + S: C360 OK Noop completed + + ...and only changes to shared flags are reported in session 3. + + C: D390 NOOP + S: * 7 FETCH (FLAGS (\Deleted) MODSEQ (12121245160)) + S: D390 OK Noop completed + + Server implementers should also see Section 3.8 for additional + quality of implementation issues related to the FETCH command. + +3.4. MODSEQ Search Criterion in SEARCH + + The MODSEQ criterion for the SEARCH command allows a client to search + for the metadata items that were modified since a specified moment. + + Syntax: MODSEQ [<entry-name> <entry-type-req>] <mod-sequence-valzer> + + Messages that have modification values that are equal to or + greater than <mod-sequence-valzer>. This allows a client, for + example, to find out which messages contain metadata items that + have changed since the last time it updated its disconnected + cache. The client may also specify <entry-name> (name of metadata + item) and <entry-type-req> (type of metadata item) before + <mod-sequence-valzer>. <entry-type-req> can be one of "shared", + "priv" (private), or "all". The latter means that the server + should use the biggest value among "priv" and "shared" mod- + sequences for the metadata item. If the server doesn't store + internally separate mod-sequences for different metadata items, it + MUST ignore <entry-name> and <entry-type-req>. Otherwise, the + server should use them to narrow down the search. + + For a flag <flagname>, the corresponding <entry-name> has a form + "/flags/<flagname>" as defined in [IMAPABNF]. Note that the + leading "\" character that denotes a system flag has to be escaped + as per Section 4.3 of [IMAP4], as the <entry-name> uses syntax for + quoted strings. + + If client specifies a MODSEQ criterion in a SEARCH command and the + server returns a non-empty SEARCH result, the server MUST also append + (to the end of the untagged SEARCH response) the highest mod-sequence + for all messages being returned. See also Section 3.5. + + + + + +Melnikov & Hole Standards Track [Page 16] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + Example 15: + + C: a SEARCH MODSEQ "/flags/\\draft" all 620162338 + S: * SEARCH 2 5 6 7 11 12 18 19 20 23 (MODSEQ 917162500) + S: a OK Search complete + + In the above example, the message numbers of any messages + containing the string "IMAP4" in the "value" attribute of the + "/comment" entry and having a mod-sequence equal to or greater + than 620162338 for the "\Draft" flag are returned in the search + results. + + Example 16: + + C: t SEARCH OR NOT MODSEQ 720162338 LARGER 50000 + S: * SEARCH + S: t OK Search complete, nothing found + +3.5. Modified SEARCH Untagged Response + + Data: zero or more numbers + mod-sequence value (omitted if no match) + + This document extends syntax of the untagged SEARCH response to + include the highest mod-sequence for all messages being returned. + + If a client specifies a MODSEQ criterion in a SEARCH (or UID SEARCH) + command and the server returns a non-empty SEARCH result, the server + MUST also append (to the end of the untagged SEARCH response) the + highest mod-sequence for all messages being returned. See Section + 3.4 for examples. + +3.6. HIGHESTMODSEQ Status Data Items + + This document defines a new status data item: + + HIGHESTMODSEQ + + The highest mod-sequence value of all messages in the mailbox. + This is the same value that is returned by the server in the + HIGHESTMODSEQ response code in an OK untagged response (see + Section 3.1.1). If the server doesn't support the persistent + storage of mod-sequences for the mailbox (see Section 3.1.2), the + server MUST return 0 as the value of HIGHESTMODSEQ status data + item. + + + + + + +Melnikov & Hole Standards Track [Page 17] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + Example 17: + + C: A042 STATUS blurdybloop (UIDNEXT MESSAGES HIGHESTMODSEQ) + S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292 + HIGHESTMODSEQ 7011231777) + S: A042 OK STATUS completed + +3.7. CONDSTORE Parameter to SELECT and EXAMINE + + The CONDSTORE extension defines a single optional select parameter, + "CONDSTORE", which tells the server that it MUST include the MODSEQ + fetch response data items in all subsequent unsolicited FETCH + responses. + + The CONDSTORE parameter to SELECT/EXAMINE helps avoid a race + condition that might arise when one or more metadata items are + modified in another session after the server has sent the + HIGHESTMODSEQ response code and before the client was able to issue a + CONDSTORE enabling command. + + Example 18: + + C: A142 SELECT INBOX (CONDSTORE) + S: * 172 EXISTS + S: * 1 RECENT + S: * OK [UNSEEN 12] Message 12 is first unseen + S: * OK [UIDVALIDITY 3857529045] UIDs valid + S: * OK [UIDNEXT 4392] Predicted next UID + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited + S: * OK [HIGHESTMODSEQ 715194045007] + S: A142 OK [READ-WRITE] SELECT completed, CONDSTORE is now enabled + +3.8. Additional Quality-of-Implementation Issues + + Server implementations should follow the following rule, which + applies to any successfully completed STORE/UID STORE (with and + without UNCHANGEDSINCE modifier), as well as to a FETCH command that + implicitly sets \Seen flag: + + Adding the flag when it is already present or removing when it is + not present SHOULD NOT change the mod-sequence. + + This will prevent spurious client synchronization requests. + + + + + + + +Melnikov & Hole Standards Track [Page 18] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + However, note that client implementers MUST NOT rely on this server + behavior. A client can't distinguish between the case when a server + has violated the SHOULD mentioned above, and that when one or more + clients set and unset (or unset and set) the flag in another session. + +4. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) [ABNF] notation. Elements not defined here can be found + in the formal syntax of the ABNF [ABNF], IMAP [IMAP4], and IMAP ABNF + extensions [IMAPABNF] specifications. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper- or lowercase characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + capability =/ "CONDSTORE" + + status-att =/ "HIGHESTMODSEQ" + ;; extends non-terminal defined in RFC 3501. + + status-att-val =/ "HIGHESTMODSEQ" SP mod-sequence-valzer + ;; extends non-terminal defined in [IMAPABNF]. + ;; Value 0 denotes that the mailbox doesn't + ;; support persistent mod-sequences + ;; as described in Section 3.1.2 + + store-modifier =/ "UNCHANGEDSINCE" SP mod-sequence-valzer + ;; Only a single "UNCHANGEDSINCE" may be + ;; specified in a STORE operation + + fetch-modifier =/ chgsince-fetch-mod + ;; conforms to the generic "fetch-modifier" + ;; syntax defined in [IMAPABNF]. + + chgsince-fetch-mod = "CHANGEDSINCE" SP mod-sequence-value + ;; CHANGEDSINCE FETCH modifier conforms to + ;; the fetch-modifier syntax + + fetch-att =/ fetch-mod-sequence + ;; modifies original IMAP4 fetch-att + + fetch-mod-sequence = "MODSEQ" + + fetch-mod-resp = "MODSEQ" SP "(" permsg-modsequence ")" + + msg-att-dynamic =/ fetch-mod-resp + + + +Melnikov & Hole Standards Track [Page 19] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + search-key =/ search-modsequence + ;; modifies original IMAP4 search-key + ;; + ;; This change applies to all commands + ;; referencing this non-terminal, in + ;; particular SEARCH. + + search-modsequence = "MODSEQ" [search-modseq-ext] SP + mod-sequence-valzer + + search-modseq-ext = SP entry-name SP entry-type-req + + resp-text-code =/ "HIGHESTMODSEQ" SP mod-sequence-value / + "NOMODSEQ" / + "MODIFIED" SP set + + entry-name = entry-flag-name + + entry-flag-name = DQUOTE "/flags/" attr-flag DQUOTE + ;; each system or user defined flag <flag> + ;; is mapped to "/flags/<flag>". + ;; + ;; <entry-flag-name> follows the escape rules + ;; used by "quoted" string as described in + ;; Section 4.3 of [IMAP4], e.g., for the flag + ;; \Seen the corresponding <entry-name> is + ;; "/flags/\\seen", and for the flag + ;; $MDNSent, the corresponding <entry-name> + ;; is "/flags/$mdnsent". + + entry-type-resp = "priv" / "shared" + ;; metadata item type + + entry-type-req = entry-type-resp / "all" + ;; perform SEARCH operation on private + ;; metadata item, shared metadata item or both + + permsg-modsequence = mod-sequence-value + ;; per message mod-sequence + + mod-sequence-value = 1*DIGIT + ;; Positive unsigned 64-bit integer + ;; (mod-sequence) + ;; (1 <= n < 18,446,744,073,709,551,615) + + mod-sequence-valzer = "0" / mod-sequence-value + + search-sort-mod-seq = "(" "MODSEQ" SP mod-sequence-value ")" + + + +Melnikov & Hole Standards Track [Page 20] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + select-param =/ condstore-param + ;; conforms to the generic "select-param" + ;; non-terminal syntax defined in [IMAPABNF]. + + condstore-param = "CONDSTORE" + + mailbox-data =/ "SEARCH" [1*(SP nz-number) SP + search-sort-mod-seq] + + attr-flag = "\\Answered" / "\\Flagged" / "\\Deleted" / + "\\Seen" / "\\Draft" / attr-flag-keyword / + attr-flag-extension + ;; Does not include "\\Recent" + + attr-flag-extension = "\\" atom + ;; Future expansion. Client implementations + ;; MUST accept flag-extension flags. Server + ;; implementations MUST NOT generate + ;; flag-extension flags except as defined by + ;; future standard or standards-track + ;; revisions of [IMAP4]. + + attr-flag-keyword = atom + +5. Server Implementation Considerations + + This section describes how a server implementation that doesn't store + separate per-metadata mod-sequences for different metadata items can + avoid sending the MODIFIED response to any of the following + conditional STORE operations: + + +FLAGS + -FLAGS + +FLAGS.SILENT + -FLAGS.SILENT + + Note that the optimization described in this section can't be + performed in case of a conditional STORE FLAGS operation. + + Let's use the following example. The client has issued + + C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) + +FLAGS.SILENT ($Processed) + + When the server receives the command and parses it successfully, it + iterates through the message set and tries to execute the conditional + STORE command for each message. + + + + +Melnikov & Hole Standards Track [Page 21] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + + Each server internally works as a client, i.e., it has to cache the + current state of all IMAP flags as it is known to the client. In + order to report flag changes to the client, the server compares the + cached values with the values in its database for IMAP flags. + + Imagine that another client has changed the state of a flag \Deleted + on the message 101 and that the change updated the mod-sequence for + the message. The server knows that the mod-sequence for the mailbox + has changed; however, it also knows that: + + a) the client is not interested in \Deleted flag, as it hasn't + included it in +FLAGS.SILENT operation; and + + b) the state of the flag $Processed hasn't changed (the server can + determine this by comparing cached flag state with the state of + the flag in the database). + + Therefore, the server doesn't have to report MODIFIED to the client. + Instead, the server may set $Processed flag, update the mod-sequence + for the message 101 once again and send an untagged FETCH response + with new mod-sequence and flags: + + S: * 101 FETCH (MODSEQ (303011130956) + FLAGS ($Processed \Deleted \Answered)) + + See also Section 3.8 for additional quality-of-implementation issues. + +6. Security Considerations + + It is believed that the Conditional STORE extension doesn't raise any + new security concerns that are not already discussed in [IMAP4]. + However, the availability of this extension may make it possible for + IMAP4 to be used in critical applications it could not be used for + previously, making correct IMAP server implementation and operation + even more important. + +7. IANA Considerations + + IMAP4 capabilities are registered by publishing a standards track or + IESG approved experimental RFC. The registry is currently located + at: + + http://www.iana.org/assignments/imap4-capabilities + + This document defines the CONDSTORE IMAP capability. IANA has added + it to the registry accordingly. + + + + + +Melnikov & Hole Standards Track [Page 22] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + +8. References + +8.1. Normative References + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 4234, October 2005. + + [IMAP4] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [IMAPABNF] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4 + ABNF", RFC 4466, April 2006. + +8.2. Informative References + + [ACAP] Newman, C. and J. Myers, "ACAP -- Application + Configuration Access Protocol", RFC 2244, November 1997. + + [ACL] Melnikov, A., "IMAP4 Access Control List (ACL) Extension", + RFC 4314, December 2005. + + [ANN] Daboo, C. and R. Gellens, "IMAP ANNOTATE Extension", Work + in Progress, March 2006. + + [NTP] Mills, D., "Network Time Protocol (Version 3) + Specification, Implementation and Analysis", RFC 1305, + March 1992. + + [RFC-2180] Gahrns, M., "IMAP4 Multi-Accessed Mailbox Practice", RFC + 2180, July 1997. + +9. Acknowledgements + + Some text was borrowed from "IMAP ANNOTATE Extension" [ANN] by + Randall Gellens and Cyrus Daboo and from "ACAP -- Application + Configuration Access Protocol" [ACAP] by Chris Newman and John Myers. + + Many thanks to Randall Gellens for his thorough review of the + document. + + The authors also acknowledge the feedback provided by Cyrus Daboo, + Larry Greenfield, Chris Newman, Harrie Hazewinkel, Arnt Gulbrandsen, + Timo Sirainen, Mark Crispin, Ned Freed, Ken Murchison, and Dave + Cridland. + + + + +Melnikov & Hole Standards Track [Page 23] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + +Authors' Addresses + + Alexey Melnikov + Isode Limited + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex + TW12 2BX, + United Kingdom + + EMail: Alexey.Melnikov@isode.com + + + Steve Hole + ACI WorldWide/MessagingDirect + #1807, 10088 102 Ave + Edmonton, AB + T5J 2Z1 + Canada + + EMail: Steve.Hole@messagingdirect.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov & Hole Standards Track [Page 24] + +RFC 4551 IMAP Extension for Conditional STORE June 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + + + +Melnikov & Hole Standards Track [Page 25] + diff --git a/imap/docs/rfc/rfc4616.txt b/imap/docs/rfc/rfc4616.txt new file mode 100644 index 00000000..991189d5 --- /dev/null +++ b/imap/docs/rfc/rfc4616.txt @@ -0,0 +1,619 @@ + + + + + + +Network Working Group K. Zeilenga, Ed. +Request for Comments: 4616 OpenLDAP Foundation +Updates: 2595 August 2006 +Category: Standards Track + + + The PLAIN Simple Authentication and Security Layer (SASL) Mechanism + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + This document defines a simple clear-text user/password Simple + Authentication and Security Layer (SASL) mechanism called the PLAIN + mechanism. The PLAIN mechanism is intended to be used, in + combination with data confidentiality services provided by a lower + layer, in protocols that lack a simple password authentication + command. + + + + + + + + + + + + + + + + + + + + + + + +Zeilenga Standards Track [Page 1] + +RFC 4616 The PLAIN SASL Mechanism August 2006 + + +1. Introduction + + Clear-text, multiple-use passwords are simple, interoperate with + almost all existing operating system authentication databases, and + are useful for a smooth transition to a more secure password-based + authentication mechanism. The drawback is that they are unacceptable + for use over network connections where data confidentiality is not + ensured. + + This document defines the PLAIN Simple Authentication and Security + Layer ([SASL]) mechanism for use in protocols with no clear-text + login command (e.g., [ACAP] or [SMTP-AUTH]). This document updates + RFC 2595, replacing Section 6. Changes since RFC 2595 are detailed + in Appendix A. + + The name associated with this mechanism is "PLAIN". + + The PLAIN SASL mechanism does not provide a security layer. + + The PLAIN mechanism should not be used without adequate data security + protection as this mechanism affords no integrity or confidentiality + protections itself. The mechanism is intended to be used with data + security protections provided by application-layer protocol, + generally through its use of Transport Layer Security ([TLS]) + services. + + By default, implementations SHOULD advertise and make use of the + PLAIN mechanism only when adequate data security services are in + place. Specifications for IETF protocols that indicate that this + mechanism is an applicable authentication mechanism MUST mandate that + implementations support an strong data security service, such as TLS. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [Keywords]. + +2. PLAIN SASL Mechanism + + The mechanism consists of a single message, a string of [UTF-8] + encoded [Unicode] characters, from the client to the server. The + client presents the authorization identity (identity to act as), + followed by a NUL (U+0000) character, followed by the authentication + identity (identity whose password will be used), followed by a NUL + (U+0000) character, followed by the clear-text password. As with + other SASL mechanisms, the client does not provide an authorization + identity when it wishes the server to derive an identity from the + credentials and use that as the authorization identity. + + + + +Zeilenga Standards Track [Page 2] + +RFC 4616 The PLAIN SASL Mechanism August 2006 + + + The formal grammar for the client message using Augmented BNF [ABNF] + follows. + + message = [authzid] UTF8NUL authcid UTF8NUL passwd + authcid = 1*SAFE ; MUST accept up to 255 octets + authzid = 1*SAFE ; MUST accept up to 255 octets + passwd = 1*SAFE ; MUST accept up to 255 octets + UTF8NUL = %x00 ; UTF-8 encoded NUL character + + SAFE = UTF1 / UTF2 / UTF3 / UTF4 + ;; any UTF-8 encoded Unicode character except NUL + + UTF1 = %x01-7F ;; except NUL + UTF2 = %xC2-DF UTF0 + UTF3 = %xE0 %xA0-BF UTF0 / %xE1-EC 2(UTF0) / + %xED %x80-9F UTF0 / %xEE-EF 2(UTF0) + UTF4 = %xF0 %x90-BF 2(UTF0) / %xF1-F3 3(UTF0) / + %xF4 %x80-8F 2(UTF0) + UTF0 = %x80-BF + + The authorization identity (authzid), authentication identity + (authcid), password (passwd), and NUL character deliminators SHALL be + transferred as [UTF-8] encoded strings of [Unicode] characters. As + the NUL (U+0000) character is used as a deliminator, the NUL (U+0000) + character MUST NOT appear in authzid, authcid, or passwd productions. + + The form of the authzid production is specific to the application- + level protocol's SASL profile [SASL]. The authcid and passwd + productions are form-free. Use of non-visible characters or + characters that a user may be unable to enter on some keyboards is + discouraged. + + Servers MUST be capable of accepting authzid, authcid, and passwd + productions up to and including 255 octets. It is noted that the + UTF-8 encoding of a Unicode character may be as long as 4 octets. + + Upon receipt of the message, the server will verify the presented (in + the message) authentication identity (authcid) and password (passwd) + with the system authentication database, and it will verify that the + authentication credentials permit the client to act as the (presented + or derived) authorization identity (authzid). If both steps succeed, + the user is authenticated. + + The presented authentication identity and password strings, as well + as the database authentication identity and password strings, are to + be prepared before being used in the verification process. The + [SASLPrep] profile of the [StringPrep] algorithm is the RECOMMENDED + preparation algorithm. The SASLprep preparation algorithm is + + + +Zeilenga Standards Track [Page 3] + +RFC 4616 The PLAIN SASL Mechanism August 2006 + + + recommended to improve the likelihood that comparisons behave in an + expected manner. The SASLprep preparation algorithm is not mandatory + so as to allow the server to employ other preparation algorithms + (including none) when appropriate. For instance, use of a different + preparation algorithm may be necessary for the server to interoperate + with an external system. + + When preparing the presented strings using [SASLPrep], the presented + strings are to be treated as "query" strings (Section 7 of + [StringPrep]) and hence unassigned code points are allowed to appear + in their prepared output. When preparing the database strings using + [SASLPrep], the database strings are to be treated as "stored" + strings (Section 7 of [StringPrep]) and hence unassigned code points + are prohibited from appearing in their prepared output. + + Regardless of the preparation algorithm used, if the output of a + non-invertible function (e.g., hash) of the expected string is + stored, the string MUST be prepared before input to that function. + + Regardless of the preparation algorithm used, if preparation fails or + results in an empty string, verification SHALL fail. + + When no authorization identity is provided, the server derives an + authorization identity from the prepared representation of the + provided authentication identity string. This ensures that the + derivation of different representations of the authentication + identity produces the same authorization identity. + + The server MAY use the credentials to initialize any new + authentication database, such as one suitable for [CRAM-MD5] or + [DIGEST-MD5]. + +3. Pseudo-Code + + This section provides pseudo-code illustrating the verification + process (using hashed passwords and the SASLprep preparation + function) discussed above. This section is not definitive. + + boolean Verify(string authzid, string authcid, string passwd) { + string pAuthcid = SASLprep(authcid, true); # prepare authcid + string pPasswd = SASLprep(passwd, true); # prepare passwd + if (pAuthcid == NULL || pPasswd == NULL) { + return false; # preparation failed + } + if (pAuthcid == "" || pPasswd == "") { + return false; # empty prepared string + } + + + + +Zeilenga Standards Track [Page 4] + +RFC 4616 The PLAIN SASL Mechanism August 2006 + + + storedHash = FetchPasswordHash(pAuthcid); + if (storedHash == NULL || storedHash == "") { + return false; # error or unknown authcid + } + + if (!Compare(storedHash, Hash(pPasswd))) { + return false; # incorrect password + } + + if (authzid == NULL ) { + authzid = DeriveAuthzid(pAuthcid); + if (authzid == NULL || authzid == "") { + return false; # could not derive authzid + } + } + + if (!Authorize(pAuthcid, authzid)) { + return false; # not authorized + } + + return true; + } + + The second parameter of the SASLprep function, when true, indicates + that unassigned code points are allowed in the input. When the + SASLprep function is called to prepare the password prior to + computing the stored hash, the second parameter would be false. + + The second parameter provided to the Authorize function is not + prepared by this code. The application-level SASL profile should be + consulted to determine what, if any, preparation is necessary. + + Note that the DeriveAuthzid and Authorize functions (whether + implemented as one function or two, whether designed in a manner in + which these functions or whether the mechanism implementation can be + reused elsewhere) require knowledge and understanding of mechanism + and the application-level protocol specification and/or + implementation details to implement. + + Note that the Authorize function outcome is clearly dependent on + details of the local authorization model and policy. Both functions + may be dependent on other factors as well. + + + + + + + + + +Zeilenga Standards Track [Page 5] + +RFC 4616 The PLAIN SASL Mechanism August 2006 + + +4. Examples + + This section provides examples of PLAIN authentication exchanges. + The examples are intended to help the readers understand the above + text. The examples are not definitive. + + "C:" and "S:" indicate lines sent by the client and server, + respectively. "<NUL>" represents a single NUL (U+0000) character. + The Application Configuration Access Protocol ([ACAP]) is used in the + examples. + + The first example shows how the PLAIN mechanism might be used for + user authentication. + + S: * ACAP (SASL "CRAM-MD5") (STARTTLS) + C: a001 STARTTLS + S: a001 OK "Begin TLS negotiation now" + <TLS negotiation, further commands are under TLS layer> + S: * ACAP (SASL "CRAM-MD5" "PLAIN") + C: a002 AUTHENTICATE "PLAIN" + S: + "" + C: {21} + C: <NUL>tim<NUL>tanstaaftanstaaf + S: a002 OK "Authenticated" + + The second example shows how the PLAIN mechanism might be used to + attempt to assume the identity of another user. In this example, the + server rejects the request. Also, this example makes use of the + protocol optional initial response capability to eliminate a round- + trip. + + S: * ACAP (SASL "CRAM-MD5") (STARTTLS) + C: a001 STARTTLS + S: a001 OK "Begin TLS negotiation now" + <TLS negotiation, further commands are under TLS layer> + S: * ACAP (SASL "CRAM-MD5" "PLAIN") + C: a002 AUTHENTICATE "PLAIN" {20+} + C: Ursel<NUL>Kurt<NUL>xipj3plmq + S: a002 NO "Not authorized to requested authorization identity" + +5. Security Considerations + + As the PLAIN mechanism itself provided no integrity or + confidentiality protections, it should not be used without adequate + external data security protection, such as TLS services provided by + many application-layer protocols. By default, implementations SHOULD + NOT advertise and SHOULD NOT make use of the PLAIN mechanism unless + adequate data security services are in place. + + + +Zeilenga Standards Track [Page 6] + +RFC 4616 The PLAIN SASL Mechanism August 2006 + + + When the PLAIN mechanism is used, the server gains the ability to + impersonate the user to all services with the same password + regardless of any encryption provided by TLS or other confidentiality + protection mechanisms. Whereas many other authentication mechanisms + have similar weaknesses, stronger SASL mechanisms address this issue. + Clients are encouraged to have an operational mode where all + mechanisms that are likely to reveal the user's password to the + server are disabled. + + General [SASL] security considerations apply to this mechanism. + + Unicode, [UTF-8], and [StringPrep] security considerations also + apply. + +6. IANA Considerations + + The SASL Mechanism registry [IANA-SASL] entry for the PLAIN mechanism + has been updated by the IANA to reflect that this document now + provides its technical specification. + + To: iana@iana.org + Subject: Updated Registration of SASL mechanism PLAIN + + SASL mechanism name: PLAIN + Security considerations: See RFC 4616. + Published specification (optional, recommended): RFC 4616 + Person & email address to contact for further information: + Kurt Zeilenga <kurt@openldap.org> + IETF SASL WG <ietf-sasl@imc.org> + Intended usage: COMMON + Author/Change controller: IESG <iesg@ietf.org> + Note: Updates existing entry for PLAIN + +7. Acknowledgements + + This document is a revision of RFC 2595 by Chris Newman. Portions of + the grammar defined in Section 2 were borrowed from [UTF-8] by + Francois Yergeau. + + This document is a product of the IETF Simple Authentication and + Security Layer (SASL) Working Group. + + + + + + + + + + +Zeilenga Standards Track [Page 7] + +RFC 4616 The PLAIN SASL Mechanism August 2006 + + +8. Normative References + + [ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", RFC 4234, October 2005. + + [Keywords] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [SASL] Melnikov, A., Ed., and K. Zeilenga, Ed., "Simple + Authentication and Security Layer (SASL)", RFC 4422, + June 2006. + + [SASLPrep] Zeilenga, K., "SASLprep: Stringprep Profile for User + Names and Passwords", RFC 4013, February 2005. + + [StringPrep] Hoffman, P. and M. Blanchet, "Preparation of + Internationalized Strings ("stringprep")", RFC 3454, + December 2002. + + [Unicode] The Unicode Consortium, "The Unicode Standard, Version + 3.2.0" is defined by "The Unicode Standard, Version + 3.0" (Reading, MA, Addison-Wesley, 2000. ISBN 0-201- + 61633-5), as amended by the "Unicode Standard Annex + #27: Unicode 3.1" + (http://www.unicode.org/reports/tr27/) and by the + "Unicode Standard Annex #28: Unicode 3.2" + (http://www.unicode.org/reports/tr28/). + + [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO + 10646", STD 63, RFC 3629, November 2003. + + [TLS] Dierks, T. and E. Rescorla, "The Transport Layer + Security (TLS) Protocol Version 1.1", RFC 4346, April + 2006. + +9. Informative References + + [ACAP] Newman, C. and J. Myers, "ACAP -- Application + Configuration Access Protocol", RFC 2244, November + 1997. + + [CRAM-MD5] Nerenberg, L., Ed., "The CRAM-MD5 SASL Mechanism", Work + in Progress, June 2006. + + [DIGEST-MD5] Melnikov, A., Ed., "Using Digest Authentication as a + SASL Mechanism", Work in Progress, June 2006. + + + + + +Zeilenga Standards Track [Page 8] + +RFC 4616 The PLAIN SASL Mechanism August 2006 + + + [IANA-SASL] IANA, "SIMPLE AUTHENTICATION AND SECURITY LAYER (SASL) + MECHANISMS", + <http://www.iana.org/assignments/sasl-mechanisms>. + + [SMTP-AUTH] Myers, J., "SMTP Service Extension for Authentication", + RFC 2554, March 1999. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Zeilenga Standards Track [Page 9] + +RFC 4616 The PLAIN SASL Mechanism August 2006 + + +Appendix A. Changes since RFC 2595 + + This appendix is non-normative. + + This document replaces Section 6 of RFC 2595. + + The specification details how the server is to compare client- + provided character strings with stored character strings. + + The ABNF grammar was updated. In particular, the grammar now allows + LINE FEED (U+000A) and CARRIAGE RETURN (U+000D) characters in the + authzid, authcid, passwd productions. However, whether these control + characters may be used depends on the string preparation rules + applicable to the production. For passwd and authcid productions, + control characters are prohibited. For authzid, one must consult the + application-level SASL profile. This change allows PLAIN to carry + all possible authorization identity strings allowed in SASL. + + Pseudo-code was added. + + The example section was expanded to illustrate more features of the + PLAIN mechanism. + +Editor's Address + + Kurt D. Zeilenga + OpenLDAP Foundation + + EMail: Kurt@OpenLDAP.org + + + + + + + + + + + + + + + + + + + + + + +Zeilenga Standards Track [Page 10] + +RFC 4616 The PLAIN SASL Mechanism August 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + + + +Zeilenga Standards Track [Page 11] + diff --git a/imap/docs/rfc/rfc4731.txt b/imap/docs/rfc/rfc4731.txt new file mode 100644 index 00000000..8c4869aa --- /dev/null +++ b/imap/docs/rfc/rfc4731.txt @@ -0,0 +1,451 @@ + + + + + + +Network Working Group A. Melnikov +Request for Comments: 4731 Isode Ltd +Category: Standards Track D. Cridland + Inventure Systems Ltd + November 2006 + + + IMAP4 Extension to SEARCH Command for Controlling + What Kind of Information Is Returned + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The IETF Trust (2006). + +Abstract + + This document extends IMAP (RFC 3501) SEARCH and UID SEARCH commands + with several result options, which can control what kind of + information is returned. The following result options are defined: + minimal value, maximal value, all found messages, and number of found + messages. + +Table of Contents + + 1. Introduction ....................................................2 + 2. Conventions Used in This Document ...............................2 + 3. IMAP Protocol Changes ...........................................2 + 3.1. New SEARCH/UID SEARCH Result Options .......................2 + 3.2. Interaction with CONDSTORE extension .......................4 + 4. Formal Syntax ...................................................5 + 5. Security Considerations .........................................6 + 6. IANA Considerations .............................................6 + 7. Normative References ............................................6 + 8. Acknowledgments .................................................6 + + + + + + + + + +Melnikov & Cridland Standards Track [Page 1] + +RFC 4731 IMAP4 Extension to SEARCH November 2006 + + +1. Introduction + + [IMAPABNF] extended SEARCH and UID SEARCH commands with result + specifiers (also known as result options), which can control what + kind of information is returned. + + A server advertising the ESEARCH capability supports the following + result options: minimal value, maximal value, all found messages, + and number of found messages. These result options allow clients to + get SEARCH results in more convenient forms, while also saving + bandwidth required to transport the results, for example, by finding + the first unseen message or returning the number of unseen or deleted + messages. Also, when a single MIN or a single MAX result option is + specified, servers can optimize execution of SEARCHes. + +2. Conventions Used in This Document + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [KEYWORDS]. + +3. IMAP Protocol Changes + +3.1. New SEARCH/UID SEARCH Result Options + + The SEARCH/UID SEARCH commands are extended to allow for the + following result options: + + MIN + Return the lowest message number/UID that satisfies the SEARCH + criteria. + + If the SEARCH results in no matches, the server MUST NOT + include the MIN result option in the ESEARCH response; however, + it still MUST send the ESEARCH response. + + MAX + Return the highest message number/UID that satisfies the SEARCH + criteria. + + If the SEARCH results in no matches, the server MUST NOT + include the MAX result option in the ESEARCH response; however, + it still MUST send the ESEARCH response. + + + + + +Melnikov & Cridland Standards Track [Page 2] + +RFC 4731 IMAP4 Extension to SEARCH November 2006 + + + ALL + Return all message numbers/UIDs that satisfy the SEARCH + criteria. Unlike regular (unextended) SEARCH, the messages are + always returned using the sequence-set syntax. A sequence-set + representation may be more compact and can be used as is in a + subsequent command that accepts sequence-set. Note, the client + MUST NOT assume that messages/UIDs will be listed in any + particular order. + + If the SEARCH results in no matches, the server MUST NOT + include the ALL result option in the ESEARCH response; however, + it still MUST send the ESEARCH response. + + COUNT + Return number of the messages that satisfy the SEARCH criteria. + This result option MUST always be included in the ESEARCH + response. + + If one or more result options described above are specified, the + extended SEARCH command MUST return a single ESEARCH response + [IMAPABNF], instead of the SEARCH response. + + An extended UID SEARCH command MUST cause an ESEARCH response with + the UID indicator present. + + Note that future extensions to this document can allow servers to + return multiple ESEARCH responses for a single extended SEARCH + command. These extensions will have to describe how results from + multiple ESEARCH responses are to be amalgamated. + + If the list of result options is empty, that requests the server to + return an ESEARCH response instead of the SEARCH response. This is + equivalent to "(ALL)". + + Example: C: A282 SEARCH RETURN (MIN COUNT) FLAGGED + SINCE 1-Feb-1994 NOT FROM "Smith" + S: * ESEARCH (TAG "A282") MIN 2 COUNT 3 + S: A282 OK SEARCH completed + + Example: C: A283 SEARCH RETURN () FLAGGED + SINCE 1-Feb-1994 NOT FROM "Smith" + S: * ESEARCH (TAG "A283") ALL 2,10:11 + S: A283 OK SEARCH completed + + The following example demonstrates finding the first unseen message + as returned in the UNSEEN response code on a successful SELECT + command: + + + + +Melnikov & Cridland Standards Track [Page 3] + +RFC 4731 IMAP4 Extension to SEARCH November 2006 + + + Example: C: A284 SEARCH RETURN (MIN) UNSEEN + S: * ESEARCH (TAG "A284") MIN 4 + S: A284 OK SEARCH completed + + The following example demonstrates that if the ESEARCH UID indicator + is present, all data in the ESEARCH response is referring to UIDs; + for example, the MIN result specifier will be followed by a UID. + + Example: C: A285 UID SEARCH RETURN (MIN MAX) 1:5000 + S: * ESEARCH (TAG "A285") UID MIN 7 MAX 3800 + S: A285 OK SEARCH completed + + The following example demonstrates returning the number of deleted + messages: + + Example: C: A286 SEARCH RETURN (COUNT) DELETED + S: * ESEARCH (TAG "A286") COUNT 15 + S: A286 OK SEARCH completed + +3.2. Interaction with CONDSTORE extension + + When the server supports both the ESEARCH and the CONDSTORE + [CONDSTORE] extension, and the client requests one or more result + option described in section 3.1 together with the MODSEQ search + criterion in the same SEARCH/UID SEARCH command, then the server MUST + return the ESEARCH response containing the MODSEQ result option + (described in the following paragraph) instead of the extended SEARCH + response described in section 3.5 of [CONDSTORE]. + + If the SEARCH/UID SEARCH command contained a single MIN or MAX result + option, the MODSEQ result option contains the mod-sequence for the + found message. If the SEARCH/UID SEARCH command contained both MIN + and MAX result options and no ALL/COUNT option, the MODSEQ result + option contains the highest mod-sequence for the two returned + messages. Otherwise the MODSEQ result option contains the highest + mod-sequence for all messages being returned. + + Example: The following example demonstrates how Example 15 from + [CONDSTORE] would look in the presence of one or more result option: + + C: a1 SEARCH RETURN (MIN) MODSEQ "/flags/\\draft" + all 620162338 + S: * ESEARCH (TAG "a1") MIN 2 MODSEQ 917162488 + S: a1 OK Search complete + + C: a2 SEARCH RETURN (MAX) MODSEQ "/flags/\\draft" + all 620162338 + S: * ESEARCH (TAG "a2") MAX 23 MODSEQ 907162321 + + + +Melnikov & Cridland Standards Track [Page 4] + +RFC 4731 IMAP4 Extension to SEARCH November 2006 + + + S: a2 OK Search complete + + C: a3 SEARCH RETURN (MIN MAX) MODSEQ "/flags/\\draft" + all 620162338 + S: * ESEARCH (TAG "a3") MIN 2 MAX 23 MODSEQ 917162488 + S: a3 OK Search complete + + C: a4 SEARCH RETURN (MIN COUNT) MODSEQ "/flags/\\draft" + all 620162338 + S: * ESEARCH (TAG "a4") MIN 2 COUNT 10 MODSEQ 917162500 + S: a4 OK Search complete + +4. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [ABNF]. + + Non-terminals referenced but not defined below are as defined by + [IMAP4], [CONDSTORE], or [IMAPABNF]. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper or lowercase characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + capability =/ "ESEARCH" + + search-return-data = "MIN" SP nz-number / + "MAX" SP nz-number / + "ALL" SP sequence-set / + "COUNT" SP number + ;; conforms to the generic + ;; search-return-data syntax defined + ;; in [IMAPABNF] + + search-return-opt = "MIN" / "MAX" / "ALL" / "COUNT" + ;; conforms to generic search-return-opt + ;; syntax defined in [IMAPABNF] + + When the CONDSTORE [CONDSTORE] IMAP extension is also supported, + the ABNF is updated as follows: + + search-return-data =/ "MODSEQ" SP mod-sequence-value + ;; mod-sequence-value is defined + ;; in [CONDSTORE] + + + + + + +Melnikov & Cridland Standards Track [Page 5] + +RFC 4731 IMAP4 Extension to SEARCH November 2006 + + +5. Security Considerations + + In the general case, the IMAP SEARCH/UID SEARCH commands can be CPU + and/or IO intensive, and are seen by some as a potential attack point + for denial of service attacks, so some sites/implementations even + disable them entirely. This is quite unfortunate, as SEARCH command + is one of the best examples demonstrating IMAP advantage over POP3. + + The ALL and COUNT return options don't change how SEARCH is working + internally; they only change how information about found messages is + returned. MIN and MAX SEARCH result options described in this + document can lighten the load on IMAP servers that choose to optimize + SEARCHes containing only one or both of them. + + It is believed that this extension doesn't raise any additional + security concerns not already discussed in [IMAP4]. + +6. IANA Considerations + + IMAP4 capabilities are registered by publishing a standards track RFC + or an IESG-approved experimental RFC. The registry is currently + located at <http://www.iana.org/assignments/imap4-capabilities>. + + This document defines the ESEARCH IMAP capability, which IANA added + to the registry. + +7. Normative References + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [IMAP4] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [ABNF] Crocker, D. (Ed.) and P. Overell , "Augmented BNF for + Syntax Specifications: ABNF", RFC 4234, October 2005. + + [IMAPABNF] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4 + ABNF", RFC 4466, April 2006.. + + [CONDSTORE] Melnikov, A. and S. Hole, "IMAP Extension for Conditional + STORE", RFC 4551, June 2006. + +8. Acknowledgments + + Thanks to Michael Wener, Arnt Gulbrandsen, Cyrus Daboo, Mark Crispin, + and Pete Maclean for comments and corrections. + + + + +Melnikov & Cridland Standards Track [Page 6] + +RFC 4731 IMAP4 Extension to SEARCH November 2006 + + +Authors' Addresses + + Alexey Melnikov + Isode Limited + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex, TW12 2BX + UK + + EMail: Alexey.Melnikov@isode.com + + + Dave A. Cridland + Inventure Systems Limited + + EMail: dave.cridland@inventuresystems.co.uk + URL: http://invsys.co.uk/dave/ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov & Cridland Standards Track [Page 7] + +RFC 4731 IMAP4 Extension to SEARCH November 2006 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST, + AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, + EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT + THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY + IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR + PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + +Melnikov & Cridland Standards Track [Page 8] + diff --git a/imap/docs/rfc/rfc4752.txt b/imap/docs/rfc/rfc4752.txt new file mode 100644 index 00000000..bfd8e30b --- /dev/null +++ b/imap/docs/rfc/rfc4752.txt @@ -0,0 +1,563 @@ + + + + + + +Network Working Group A. Melnikov, Ed. +Request for Comments: 4752 Isode +Obsoletes: 2222 November 2006 +Category: Standards Track + + + The Kerberos V5 ("GSSAPI") + Simple Authentication and Security Layer (SASL) Mechanism + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The IETF Trust (2006). + +Abstract + + The Simple Authentication and Security Layer (SASL) is a framework + for adding authentication support to connection-based protocols. + This document describes the method for using the Generic Security + Service Application Program Interface (GSS-API) Kerberos V5 in the + SASL. + + This document replaces Section 7.2 of RFC 2222, the definition of the + "GSSAPI" SASL mechanism. This document, together with RFC 4422, + obsoletes RFC 2222. + + + + + + + + + + + + + + + + + + + +Melnikov Standards Track [Page 1] + +RFC 4752 SASL GSSAPI Mechanism November 2006 + + +Table of Contents + + 1. Introduction ....................................................2 + 1.1. Relationship to Other Documents ............................2 + 2. Conventions Used in This Document ...............................2 + 3. Kerberos V5 GSS-API Mechanism ...................................2 + 3.1. Client Side of Authentication Protocol Exchange ............3 + 3.2. Server Side of Authentication Protocol Exchange ............4 + 3.3. Security Layer .............................................6 + 4. IANA Considerations .............................................7 + 5. Security Considerations .........................................7 + 6. Acknowledgements ................................................8 + 7. Changes since RFC 2222 ..........................................8 + 8. References ......................................................8 + 8.1. Normative References .......................................8 + 8.2. Informative References .....................................9 + +1. Introduction + + This specification documents currently deployed Simple Authentication + and Security Layer (SASL [SASL]) mechanism supporting the Kerberos V5 + [KERBEROS] Generic Security Service Application Program Interface + ([GSS-API]) mechanism [RFC4121]. The authentication sequence is + described in Section 3. Note that the described authentication + sequence has known limitations, in particular, it lacks channel + bindings and the number of round-trips required to complete + authentication exchange is not minimal. SASL WG is working on a + separate document that should address these limitations. + +1.1. Relationship to Other Documents + + This document, together with RFC 4422, obsoletes RFC 2222 in its + entirety. This document replaces Section 7.2 of RFC 2222. The + remainder is obsoleted as detailed in Section 1.2 of RFC 4422. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" + in this document are to be interpreted as defined in "Key words for + use in RFCs to Indicate Requirement Levels" [KEYWORDS]. + +3. Kerberos V5 GSS-API Mechanism + + The SASL mechanism name for the Kerberos V5 GSS-API mechanism + [RFC4121] is "GSSAPI". Though known as the SASL GSSAPI mechanism, + the mechanism is specifically tied to Kerberos V5 and GSS-API's + Kerberos V5 mechanism. + + + + +Melnikov Standards Track [Page 2] + +RFC 4752 SASL GSSAPI Mechanism November 2006 + + + The GSSAPI SASL mechanism is a "client goes first" SASL mechanism; + i.e., it starts with the client sending a "response" created as + described in the following section. + + The implementation MAY set any GSS-API flags or arguments not + mentioned in this specification as is necessary for the + implementation to enforce its security policy. + + Note that major status codes returned by GSS_Init_sec_context() or + GSS_Accept_sec_context() other than GSS_S_COMPLETE or + GSS_S_CONTINUE_NEEDED cause authentication failure. Major status + codes returned by GSS_Unwrap() other than GSS_S_COMPLETE (without any + additional supplementary status codes) cause authentication and/or + security layer failure. + +3.1. Client Side of Authentication Protocol Exchange + + The client calls GSS_Init_sec_context, passing in + input_context_handle of 0 (initially), mech_type of the Kerberos V5 + GSS-API mechanism [KRB5GSS], chan_binding of NULL, and targ_name + equal to output_name from GSS_Import_Name called with input_name_type + of GSS_C_NT_HOSTBASED_SERVICE (*) and input_name_string of + "service@hostname" where "service" is the service name specified in + the protocol's profile, and "hostname" is the fully qualified host + name of the server. When calling the GSS_Init_sec_context, the + client MUST pass the integ_req_flag of TRUE (**). If the client will + be requesting a security layer, it MUST also supply to the + GSS_Init_sec_context a mutual_req_flag of TRUE, and a + sequence_req_flag of TRUE. If the client will be requesting a + security layer providing confidentiality protection, it MUST also + supply to the GSS_Init_sec_context a conf_req_flag of TRUE. The + client then responds with the resulting output_token. If + GSS_Init_sec_context returns GSS_S_CONTINUE_NEEDED, then the client + should expect the server to issue a token in a subsequent challenge. + The client must pass the token to another call to + GSS_Init_sec_context, repeating the actions in this paragraph. + + (*) Clients MAY use name types other than GSS_C_NT_HOSTBASED_SERVICE + to import servers' acceptor names, but only when they have a priori + knowledge that the servers support alternate name types. Otherwise + clients MUST use GSS_C_NT_HOSTBASED_SERVICE for importing acceptor + names. + + (**) Note that RFC 2222 [RFC2222] implementations will not work with + GSS-API implementations that require integ_req_flag to be true. No + implementations of RFC 1964 [KRB5GSS] or RFC 4121 [RFC4121] that + require integ_req_flag to be true are believed to exist and it is + expected that any future update to [RFC4121] will require that + + + +Melnikov Standards Track [Page 3] + +RFC 4752 SASL GSSAPI Mechanism November 2006 + + + integrity be available even in not explicitly requested by the + application. + + When GSS_Init_sec_context returns GSS_S_COMPLETE, the client examines + the context to ensure that it provides a level of protection + permitted by the client's security policy. In particular, if the + integ_avail flag is not set in the context, then no security layer + can be offered or accepted. + + If the conf_avail flag is not set in the context, then no security + layer with confidentiality can be offered or accepted. If the + context is acceptable, the client takes the following actions: If the + last call to GSS_Init_sec_context returned an output_token, then the + client responds with the output_token, otherwise the client responds + with no data. The client should then expect the server to issue a + token in a subsequent challenge. The client passes this token to + GSS_Unwrap and interprets the first octet of resulting cleartext as a + bit-mask specifying the security layers supported by the server and + the second through fourth octets as the maximum size output_message + the server is able to receive (in network byte order). If the + resulting cleartext is not 4 octets long, the client fails the + negotiation. The client verifies that the server maximum buffer is 0 + if the server does not advertise support for any security layer. + + The client then constructs data, with the first octet containing the + bit-mask specifying the selected security layer, the second through + fourth octets containing in network byte order the maximum size + output_message the client is able to receive (which MUST be 0 if the + client does not support any security layer), and the remaining octets + containing the UTF-8 [UTF8] encoded authorization identity. + (Implementation note: The authorization identity is not terminated + with the zero-valued (%x00) octet (e.g., the UTF-8 encoding of the + NUL (U+0000) character)). The client passes the data to GSS_Wrap + with conf_flag set to FALSE and responds with the generated + output_message. The client can then consider the server + authenticated. + +3.2. Server Side of Authentication Protocol Exchange + + A server MUST NOT advertise support for the "GSSAPI" SASL mechanism + described in this document unless it has acceptor credential for the + Kerberos V GSS-API mechanism [KRB5GSS]. + + The server passes the initial client response to + GSS_Accept_sec_context as input_token, setting input_context_handle + to 0 (initially), chan_binding of NULL, and a suitable + acceptor_cred_handle (see below). If GSS_Accept_sec_context returns + GSS_S_CONTINUE_NEEDED, the server returns the generated output_token + + + +Melnikov Standards Track [Page 4] + +RFC 4752 SASL GSSAPI Mechanism November 2006 + + + to the client in challenge and passes the resulting response to + another call to GSS_Accept_sec_context, repeating the actions in this + paragraph. + + Servers SHOULD use a credential obtained by calling GSS_Acquire_cred + or GSS_Add_cred for the GSS_C_NO_NAME desired_name and the Object + Identifier (OID) of the Kerberos V5 GSS-API mechanism [KRB5GSS](*). + Servers MAY use GSS_C_NO_CREDENTIAL as an acceptor credential handle. + Servers MAY use a credential obtained by calling GSS_Acquire_cred or + GSS_Add_cred for the server's principal name(s) (**) and the Kerberos + V5 GSS-API mechanism [KRB5GSS]. + + (*) Unlike GSS_Add_cred the GSS_Acquire_cred uses an OID set of GSS- + API mechanism as an input parameter. The OID set can be created by + using GSS_Create_empty_OID_set and GSS_Add_OID_set_member. It can be + freed by calling the GSS_Release_oid_set. + + + (**) Use of server's principal names having + GSS_C_NT_HOSTBASED_SERVICE name type and "service@hostname" format, + where "service" is the service name specified in the protocol's + profile, and "hostname" is the fully qualified host name of the + server, is RECOMMENDED. The server name is generated by calling + GSS_Import_name with input_name_type of GSS_C_NT_HOSTBASED_SERVICE + and input_name_string of "service@hostname". + + Upon successful establishment of the security context (i.e., + GSS_Accept_sec_context returns GSS_S_COMPLETE), the server SHOULD + verify that the negotiated GSS-API mechanism is indeed Kerberos V5 + [KRB5GSS]. This is done by examining the value of the mech_type + parameter returned from the GSS_Accept_sec_context call. If the + value differs, SASL authentication MUST be aborted. + + Upon successful establishment of the security context and if the + server used GSS_C_NO_NAME/GSS_C_NO_CREDENTIAL to create acceptor + credential handle, the server SHOULD also check using the + GSS_Inquire_context that the target_name used by the client matches + either + + - the GSS_C_NT_HOSTBASED_SERVICE "service@hostname" name syntax, + where "service" is the service name specified in the application + protocol's profile, + + or + + - the GSS_KRB5_NT_PRINCIPAL_NAME [KRB5GSS] name syntax for a two- + component principal where the first component matches the service + name specified in the application protocol's profile. + + + +Melnikov Standards Track [Page 5] + +RFC 4752 SASL GSSAPI Mechanism November 2006 + + + When GSS_Accept_sec_context returns GSS_S_COMPLETE, the server + examines the context to ensure that it provides a level of protection + permitted by the server's security policy. In particular, if the + integ_avail flag is not set in the context, then no security layer + can be offered or accepted. If the conf_avail flag is not set in the + context, then no security layer with confidentiality can be offered + or accepted. + + If the context is acceptable, the server takes the following actions: + If the last call to GSS_Accept_sec_context returned an output_token, + the server returns it to the client in a challenge and expects a + reply from the client with no data. Whether or not an output_token + was returned (and after receipt of any response from the client to + such an output_token), the server then constructs 4 octets of data, + with the first octet containing a bit-mask specifying the security + layers supported by the server and the second through fourth octets + containing in network byte order the maximum size output_token the + server is able to receive (which MUST be 0 if the server does not + support any security layer). The server must then pass the plaintext + to GSS_Wrap with conf_flag set to FALSE and issue the generated + output_message to the client in a challenge. + + The server must then pass the resulting response to GSS_Unwrap and + interpret the first octet of resulting cleartext as the bit-mask for + the selected security layer, the second through fourth octets as the + maximum size output_message the client is able to receive (in network + byte order), and the remaining octets as the authorization identity. + The server verifies that the client has selected a security layer + that was offered and that the client maximum buffer is 0 if no + security layer was chosen. The server must verify that the src_name + is authorized to act as the authorization identity. After these + verifications, the authentication process is complete. The server is + not expected to return any additional data with the success + indicator. + +3.3. Security Layer + + The security layers and their corresponding bit-masks are as follows: + + 1 No security layer + 2 Integrity protection. + Sender calls GSS_Wrap with conf_flag set to FALSE + 4 Confidentiality protection. + Sender calls GSS_Wrap with conf_flag set to TRUE + + Other bit-masks may be defined in the future; bits that are not + understood must be negotiated off. + + + + +Melnikov Standards Track [Page 6] + +RFC 4752 SASL GSSAPI Mechanism November 2006 + + + When decoding any received data with GSS_Unwrap, the major_status + other than the GSS_S_COMPLETE MUST be treated as a fatal error. + + Note that SASL negotiates the maximum size of the output_message to + send. Implementations can use the GSS_Wrap_size_limit call to + determine the corresponding maximum size input_message. + +4. IANA Considerations + + IANA modified the existing registration for "GSSAPI" as follows: + + Family of SASL mechanisms: NO + + SASL mechanism name: GSSAPI + + Security considerations: See Section 5 of RFC 4752 + + Published specification: RFC 4752 + + Person & email address to contact for further information: + Alexey Melnikov <Alexey.Melnikov@isode.com> + + Intended usage: COMMON + + Owner/Change controller: iesg@ietf.org + + Additional information: This mechanism is for the Kerberos V5 + mechanism of GSS-API. + +5. Security Considerations + + Security issues are discussed throughout this memo. + + When constructing the input_name_string, the client SHOULD NOT + canonicalize the server's fully qualified domain name using an + insecure or untrusted directory service. + + For compatibility with deployed software, this document requires that + the chan_binding (channel bindings) parameter to GSS_Init_sec_context + and GSS_Accept_sec_context be NULL, hence disallowing use of GSS-API + support for channel bindings. GSS-API channel bindings in SASL is + expected to be supported via a new GSS-API family of SASL mechanisms + (to be introduced in a future document). + + Additional security considerations are in the [SASL] and [GSS-API] + specifications. Additional security considerations for the GSS-API + mechanism can be found in [KRB5GSS] and [KERBEROS]. + + + + +Melnikov Standards Track [Page 7] + +RFC 4752 SASL GSSAPI Mechanism November 2006 + + +6. Acknowledgements + + This document replaces Section 7.2 of RFC 2222 [RFC2222] by John G. + Myers. He also contributed significantly to this revision. + + Lawrence Greenfield converted text of this document to the XML + format. + + Contributions of many members of the SASL mailing list are gratefully + acknowledged, in particular comments from Chris Newman, Nicolas + Williams, Jeffrey Hutzelman, Sam Hartman, Mark Crispin, and Martin + Rex. + +7. Changes since RFC 2222 + + RFC 2078 [RFC2078] specifies the version of GSS-API used by RFC 2222 + [RFC2222], which provided the original version of this specification. + That version of GSS-API did not provide the integ_integ_avail flag as + an input to GSS_Init_sec_context. Instead, integrity was always + requested. RFC 4422 [SASL] requires that when possible, the security + layer negotiation be integrity protected. To meet this requirement + and as part of moving from RFC 2078 [RFC2078] to RFC 2743 [GSS-API], + this specification requires that clients request integrity from + GSS_Init_sec_context so they can use GSS_Wrap to protect the security + layer negotiation. This specification does not require that the + mechanism offer the integrity security layer, simply that the + security layer negotiation be wrapped. + +8. References + +8.1. Normative References + + [GSS-API] Linn, J., "Generic Security Service Application Program + Interface Version 2, Update 1", RFC 2743, January 2000. + + [KERBEROS] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The + Kerberos Network Authentication Service (V5)", RFC 4120, + July 2005. + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [KRB5GSS] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", RFC + 1964, June 1996. + + + + + + + +Melnikov Standards Track [Page 8] + +RFC 4752 SASL GSSAPI Mechanism November 2006 + + + [RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos + Version 5 Generic Security Service Application Program + Interface (GSS-API) Mechanism: Version 2", RFC 4121, July + 2005. + + [SASL] Melnikov, A. and K. Zeilenga, "Simple Authentication and + Security Layer (SASL)", RFC 4422, June 2006. + + [UTF8] Yergeau, F., "UTF-8, a transformation format of ISO + 10646", STD 63, RFC 3629, November 2003. + +8.2. Informative References + + [RFC2078] Linn, J., "Generic Security Service Application Program + Interface, Version 2", RFC 2078, January 1997. + + [RFC2222] Myers, J., "Simple Authentication and Security Layer + (SASL)", RFC 2222, October 1997. + +Editor's Address + + Alexey Melnikov + Isode Limited + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: Alexey.Melnikov@isode.com + URI: http://www.melnikov.ca/ + + + + + + + + + + + + + + + + + + + + + +Melnikov Standards Track [Page 9] + +RFC 4752 SASL GSSAPI Mechanism November 2006 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST, + AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, + EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT + THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY + IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR + PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + +Melnikov Standards Track [Page 10] + diff --git a/imap/docs/rfc/rfc4790.txt b/imap/docs/rfc/rfc4790.txt new file mode 100644 index 00000000..d58191c0 --- /dev/null +++ b/imap/docs/rfc/rfc4790.txt @@ -0,0 +1,1459 @@ + + + + + + +Network Working Group C. Newman +Request for Comments: 4790 Sun Microsystems +Category: Standards Track M. Duerst + Aoyama Gakuin University + A. Gulbrandsen + Oryx + March 2007 + + + Internet Application Protocol Collation Registry + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The IETF Trust (2007). + +Abstract + + Many Internet application protocols include string-based lookup, + searching, or sorting operations. However, the problem space for + searching and sorting international strings is large, not fully + explored, and is outside the area of expertise for the Internet + Engineering Task Force (IETF). Rather than attempt to solve such a + large problem, this specification creates an abstraction framework so + that application protocols can precisely identify a comparison + function, and the repertoire of comparison functions can be extended + in the future. + + + + + + + + + + + + + + + + + +Newman, et al. Standards Track [Page 1] + +RFC 4790 Collation Registry March 2007 + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 + 1.1. Conventions Used in This Document . . . . . . . . . . . . 4 + 2. Collation Definition and Purpose . . . . . . . . . . . . . . . 4 + 2.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 4 + 2.2. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 4 + 2.3. Some Other Terms Used in this Document . . . . . . . . . . 5 + 2.4. Sort Keys . . . . . . . . . . . . . . . . . . . . . . . . 5 + 3. Collation Identifier Syntax . . . . . . . . . . . . . . . . . 6 + 3.1. Basic Syntax . . . . . . . . . . . . . . . . . . . . . . . 6 + 3.2. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . 6 + 3.3. Ordering Direction . . . . . . . . . . . . . . . . . . . . 7 + 3.4. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 + 3.5. Naming Guidelines . . . . . . . . . . . . . . . . . . . . 7 + 4. Collation Specification Requirements . . . . . . . . . . . . . 8 + 4.1. Collation/Server Interface . . . . . . . . . . . . . . . . 8 + 4.2. Operations Supported . . . . . . . . . . . . . . . . . . . 8 + 4.2.1. Validity . . . . . . . . . . . . . . . . . . . . . . . 9 + 4.2.2. Equality . . . . . . . . . . . . . . . . . . . . . . . 9 + 4.2.3. Substring . . . . . . . . . . . . . . . . . . . . . . 9 + 4.2.4. Ordering . . . . . . . . . . . . . . . . . . . . . . . 10 + 4.3. Sort Keys . . . . . . . . . . . . . . . . . . . . . . . . 10 + 4.4. Use of Lookup Tables . . . . . . . . . . . . . . . . . . . 11 + 5. Application Protocol Requirements . . . . . . . . . . . . . . 11 + 5.1. Character Encoding . . . . . . . . . . . . . . . . . . . . 11 + 5.2. Operations . . . . . . . . . . . . . . . . . . . . . . . . 11 + 5.3. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . 12 + 5.4. String Comparison . . . . . . . . . . . . . . . . . . . . 12 + 5.5. Disconnected Clients . . . . . . . . . . . . . . . . . . . 12 + 5.6. Error Codes . . . . . . . . . . . . . . . . . . . . . . . 13 + 5.7. Octet Collation . . . . . . . . . . . . . . . . . . . . . 13 + 6. Use by Existing Protocols . . . . . . . . . . . . . . . . . . 13 + 7. Collation Registration . . . . . . . . . . . . . . . . . . . . 14 + 7.1. Collation Registration Procedure . . . . . . . . . . . . . 14 + 7.2. Collation Registration Format . . . . . . . . . . . . . . 15 + 7.2.1. Registration Template . . . . . . . . . . . . . . . . 15 + 7.2.2. The Collation Element . . . . . . . . . . . . . . . . 15 + 7.2.3. The Identifier Element . . . . . . . . . . . . . . . . 16 + 7.2.4. The Title Element . . . . . . . . . . . . . . . . . . 16 + 7.2.5. The Operations Element . . . . . . . . . . . . . . . . 16 + 7.2.6. The Specification Element . . . . . . . . . . . . . . 16 + 7.2.7. The Submitter Element . . . . . . . . . . . . . . . . 16 + 7.2.8. The Owner Element . . . . . . . . . . . . . . . . . . 16 + 7.2.9. The Version Element . . . . . . . . . . . . . . . . . 17 + 7.2.10. The Variable Element . . . . . . . . . . . . . . . . . 17 + 7.3. Structure of Collation Registry . . . . . . . . . . . . . 17 + 7.4. Example Initial Registry Summary . . . . . . . . . . . . . 18 + + + +Newman, et al. Standards Track [Page 2] + +RFC 4790 Collation Registry March 2007 + + + 8. Guidelines for Expert Reviewer . . . . . . . . . . . . . . . . 18 + 9. Initial Collations . . . . . . . . . . . . . . . . . . . . . . 19 + 9.1. ASCII Numeric Collation . . . . . . . . . . . . . . . . . 20 + 9.1.1. ASCII Numeric Collation Description . . . . . . . . . 20 + 9.1.2. ASCII Numeric Collation Registration . . . . . . . . . 20 + 9.2. ASCII Casemap Collation . . . . . . . . . . . . . . . . . 21 + 9.2.1. ASCII Casemap Collation Description . . . . . . . . . 21 + 9.2.2. ASCII Casemap Collation Registration . . . . . . . . . 22 + 9.3. Octet Collation . . . . . . . . . . . . . . . . . . . . . 22 + 9.3.1. Octet Collation Description . . . . . . . . . . . . . 22 + 9.3.2. Octet Collation Registration . . . . . . . . . . . . . 23 + 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 + 11. Security Considerations . . . . . . . . . . . . . . . . . . . 23 + 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23 + 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24 + 13.1. Normative References . . . . . . . . . . . . . . . . . . . 24 + 13.2. Informative References . . . . . . . . . . . . . . . . . . 24 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Newman, et al. Standards Track [Page 3] + +RFC 4790 Collation Registry March 2007 + + +1. Introduction + + The Application Configuration Access Protocol ACAP [11] specification + introduced the concept of a comparator (which we call collation in + this document), but failed to create an IANA registry. With the + introduction of stringprep [6] and the Unicode Collation Algorithm + [7], it is now time to create that registry and populate it with some + initial values appropriate for an international community. This + specification replaces and generalizes the definition of a comparator + in ACAP, and creates a collation registry. + +1.1. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" + in this document are to be interpreted as defined in "Key words for + use in RFCs to Indicate Requirement Levels" [1]. + + The attribute syntax specifications use the Augmented Backus-Naur + Form (ABNF) [2] notation, including the core rules defined in + Appendix A. The ABNF production "Language-tag" is imported from + Language Tags [5] and "reg-name" from URI: Generic Syntax [4]. + +2. Collation Definition and Purpose + +2.1. Definition + + A collation is a named function which takes two arbitrary length + strings as input and can be used to perform one or more of three + basic comparison operations: equality test, substring match, and + ordering test. + +2.2. Purpose + + Collations are an abstraction for comparison functions so that these + comparison functions can be used in multiple protocols. The details + of a particular comparison operation can be specified by someone with + appropriate expertise, independent of the application protocols that + use that collation. This is similar to the way a charset [13] + separates the details of octet to character mapping from a protocol + specification, such as MIME [9], or the way SASL [10] separates the + details of an authentication mechanism from a protocol specification, + such as ACAP [11]. + + + + + + + + + +Newman, et al. Standards Track [Page 4] + +RFC 4790 Collation Registry March 2007 + + + Here is a small diagram to help illustrate the value of this + abstraction: + + +-------------------+ +-----------------+ + | IMAP i18n SEARCH |--+ | Basic | + +-------------------+ | +--| Collation Spec | + | | +-----------------+ + +-------------------+ | +-------------+ | +-----------------+ + | ACAP i18n SEARCH |--+--| Collation |--+--| A stringprep | + +-------------------+ | | Registry | | | Collation Spec | + | +-------------+ | +-----------------+ + +-------------------+ | | +-----------------+ + | ...other protocol |--+ | | locale-specific | + +-------------------+ +--| Collation Spec | + +-----------------+ + + Thus IMAP, ACAP, and future application protocols with international + search capability simply specify how to interface to the collation + registry instead of each protocol specification having to specify all + the collations it supports. + +2.3. Some Other Terms Used in this Document + + The terms client, server, and protocol are used in somewhat unusual + senses. + + Client means a user, or a program acting directly on behalf of a + user. This may be a mail reader acting as an IMAP client, or it may + be an interactive shell, where the user can type protocol commands/ + requests directly, or it may be a script or program written by the + user. + + Server means a program that performs services requested by the + client. This may be a traditional server such as an HTTP server, or + it may be a Sieve [14] interpreter running a Sieve script written by + a user. A server needs to use the operations provided by collations + in order to fulfill the client's requests. + + The protocol describes how the client tells the server what it wants + done, and (if applicable) how the server tells the client about the + results. IMAP is a protocol by this definition, and so is the Sieve + language. + +2.4. Sort Keys + + One component of a collation is a transformation, which turns a + string into a sort key, which is then used while sorting. + + + + +Newman, et al. Standards Track [Page 5] + +RFC 4790 Collation Registry March 2007 + + + The transformation can range from an identity mapping (e.g., the + i;octet collation Section 9.3) to a mapping that makes the string + unreadable to a human. + + This is an implementation detail of collations or servers. A + protocol SHOULD NOT expose it to clients, since some collations leave + the sort key's format up to the implementation, and current + conformant implementations are known to use different formats. + +3. Collation Identifier Syntax + +3.1. Basic Syntax + + The collation identifier itself is a single US-ASCII string. The + identifier MUST NOT be longer than 254 characters, and obeys the + following grammar: + + collation-char = ALPHA / DIGIT / "-" / ";" / "=" / "." + + collation-id = collation-prefix ";" collation-core-name + *collation-arg + + collation-scope = Language-tag / "vnd-" reg-name + + collation-core-name = ALPHA *( ALPHA / DIGIT / "-" ) + + collation-arg = ";" ALPHA *( ALPHA / DIGIT ) "=" + 1*( ALPHA / DIGIT / "." ) + + + Note: the ABNF production "Language-tag" is imported from Language + Tags [5] and "reg-name" from URI: Generic Syntax [4]. + + There is a special identifier called "default". For protocols that + have a default collation, "default" refers to that collation. For + other protocols, the identifier "default" MUST match no collations, + and servers SHOULD treat it in the same way as they treat nonexistent + collations. + +3.2. Wildcards + + The string a client uses to select a collation MAY contain one or + more wildcard ("*") characters that match zero or more collation- + chars. Wildcard characters MUST NOT be adjacent. If the wildcard + string matches multiple collations, the server SHOULD attempt to + select a widely useful collation in preference to a narrowly useful + one. + + + + +Newman, et al. Standards Track [Page 6] + +RFC 4790 Collation Registry March 2007 + + + collation-wild = ("*" / (ALPHA ["*"])) *(collation-char ["*"]) + ; MUST NOT exceed 254 characters total + +3.3. Ordering Direction + + When used as a protocol element for ordering, the collation + identifier MAY be prefixed by either "+" or "-" to explicitly specify + an ordering direction. "+" has no effect on the ordering operation, + while "-" inverts the result of the ordering operation. In general, + collation-order is used when a client requests a collation, and + collation-selected is used when the server informs the client of the + selected collation. + + collation-selected = ["+" / "-"] collation-id + + collation-order = ["+" / "-"] collation-wild + +3.4. URIs + + Some protocols are designed to use URIs [4] to refer to collations + rather than simple tokens. A special section of the IANA URL space + is reserved for such usage. The "collation-uri" form is used to + refer to a specific named collation (the collation registration may + not actually be present). The "collation-auri" form is an abstract + name for an ordering, a collation pattern or a vendor private + collator. + + collation-uri = "http://www.iana.org/assignments/collation/" + collation-id ".xml" + + collation-auri = ( "http://www.iana.org/assignments/collation/" + collation-order ".xml" ) / other-uri + + other-uri = <absoluteURI> + ; excluding the IANA collation namespace. + +3.5. Naming Guidelines + + While this specification makes no absolute requirements on the + structure of collation identifiers, naming consistency is important, + so the following initial guidelines are provided. + + Collation identifiers with an international audience typically begin + with "i;". Collation identifiers intended for a particular language + or locale typically begin with a language tag [5] followed by a ";". + After the first ";" is normally the name of the general collation + algorithm, followed by a series of algorithm modifications separated + by the ";" delimiter. Parameterized modifications will use "=" to + + + +Newman, et al. Standards Track [Page 7] + +RFC 4790 Collation Registry March 2007 + + + delimit the parameter from the value. The version numbers of any + lookup tables used by the algorithm SHOULD be present as + parameterized modifications. + + Collation identifiers of the form *;vnd-hostname;* are reserved for + vendor-specific collations created by the owner of the hostname + following the "vnd-" prefix (e.g., vnd-example.com for the vendor + example.com). Registration of such collations (or the name space as + a whole), with intended use of the "Vendor", is encouraged when a + public specification or open-source implementation is available, but + is not required. + +4. Collation Specification Requirements + +4.1. Collation/Server Interface + + The collation itself defines what it operates on. Most collations + are expected to operate on character strings. The i;octet + (Section 9.3) collation operates on octet strings. The i;ascii- + numeric (Section 9.1) operation operates on numbers. + + This specification defines the collation interface in terms of octet + strings. However, implementations may choose to use character + strings instead. Such implementations may not be able to implement + e.g., i;octet. Since i;octet is not currently mandatory to implement + for any protocol, this should not be a problem. + +4.2. Operations Supported + + A collation specification MUST state which of the three basic + operations are supported (equality, substring, ordering) and how to + perform each of the supported operations on any two input character + strings, including empty strings. Collations must be deterministic, + i.e., given a collation with a specific identifier, and any two fixed + input strings, the result MUST be the same for the same operation. + + In general, collation operations should behave as their names + suggest. While a collation may be new, the operations are not, so + the new collation's operations should be similar to those of older + collations. For example, a date/time collation should not provide a + "substring" operation that would morph IMAP substring SEARCH into + e.g., a date-range search. + + A non-obvious consequence of the rules for each collation operation + is that, for any single collation, either none or all of the + operations can return "undefined". For example, it is not possible + to have an equality operation that never returns "undefined", and a + substring operation that occasionally does. + + + +Newman, et al. Standards Track [Page 8] + +RFC 4790 Collation Registry March 2007 + + +4.2.1. Validity + + The validity test takes one string as argument. It returns valid if + its input string is a valid input to the collation's other + operations, and invalid if not. (In other words, a string is valid + if it is equal to itself according to the collation's equality + operation.) + + The validity test is provided by all collations. It MUST NOT be + listed separately in the collation registration. + +4.2.2. Equality + + The equality test always returns "match" or "no-match" when it is + supplied valid input, and MAY return "undefined" if one or both input + strings are not valid. + + The equality test MUST be reflexive and symmetric. For valid input, + it MUST be transitive. + + If a collation provides either a substring or an ordering test, it + MUST also provide an equality test. The substring and/or ordering + tests MUST be consistent with the equality test. + + The return values of the equality test are called "match", "no-match" + and "undefined" in this document. + +4.2.3. Substring + + The substring matching operation determines if the first string is a + substring of the second string, i.e., if one or more substrings of + the second string is equal to the first, as defined by the + collation's equality operation. + + A collation that supports substring matching will automatically + support two special cases of substring matching: prefix and suffix + matching, if those special cases are supported by the application + protocol. It returns "match" or "no-match" when it is supplied valid + input and returns "undefined" when supplied invalid input. + + Application protocols MAY return position information for substring + matches. If this is done, the position information SHOULD include + both the starting offset and the ending offset for each match. This + is important because more sophisticated collations can match strings + of unequal length (for example, a pre-composed accented character can + match a decomposed accented character). In general, overlapping + matches SHOULD be reported (as when "ana" occurs twice within + "banana"), although there are cases where a collation may decide not + + + +Newman, et al. Standards Track [Page 9] + +RFC 4790 Collation Registry March 2007 + + + to. For example, in a collation which treats all whitespace + sequences as identical, the substring operation could be defined such + that " 1 " (SP "1" SP) is reported just once within " 1 " (SP SP + "1" SP SP), not four times (SP SP "1" SP, SP "1" SP, SP "1" SP SP and + SP SP "1" SP SP), since the four matches are, in a sense, the same + match. + + A string is a substring of itself. The empty string is a substring + of all strings. + + Note that the substring operation of some collations can match + strings of unequal length. For example, a pre-composed accented + character can match a decomposed accented character. The Unicode + Collation Algorithm [7] discusses this in more detail. + + The return values of the substring operation are called "match", "no- + match", and "undefined" in this document. + +4.2.4. Ordering + + The ordering operation determines how two strings are ordered. It + MUST be reflexive. For valid input, it MUST be transitive and + trichotomous. + + Ordering returns "less" if the first string is listed before the + second string, according to the collation; "greater", if the second + string is listed before the first string; and "equal", if the two + strings are equal, as defined by the collation's equality operation. + If one or both strings are invalid, the result of ordering is + "undefined". + + When the collation is used with a "+" prefix, the behavior is the + same as when used with no prefix. When the collation is used with a + "-" prefix, the result of the ordering operation of the collation + MUST be reversed. + + The return values of the ordering operation are called "less", + "equal", "greater", and "undefined" in this document. + +4.3. Sort Keys + + A collation specification SHOULD describe the internal transformation + algorithm to generate sort keys. This algorithm can be applied to + individual strings, and the result can be stored to potentially + optimize future comparison operations. A collation MAY specify that + the sort key is generated by the identity function. The sort key may + have no meaning to a human. The sort key may not be valid input to + the collation. + + + +Newman, et al. Standards Track [Page 10] + +RFC 4790 Collation Registry March 2007 + + +4.4. Use of Lookup Tables + + Some collations use customizable lookup tables, e.g., because the + tables depend on locale, and may be modified after shipping the + software. Collations that use more than one customizable lookup + table in a documented format MUST assign numbers to the tables they + use. This permits an application protocol command to access the + tables used by a server collation, so that clients and servers use + the same tables. + +5. Application Protocol Requirements + + This section describes the requirements and issues that an + application protocol needs to consider if it offers searching, + substring matching and/or sorting, and permits the use of characters + outside the US-ASCII charset. + +5.1. Character Encoding + + The protocol specification has to make sure that it is clear on which + characters (rather than just octets) the collations are used. This + can be done by specifying the protocol itself in terms of characters + (e.g., in the case of a query language), by specifying a single + character encoding for the protocol (e.g., UTF-8 [3]), or by + carefully describing the relevant issues of character encoding + labeling and conversion. In the later case, details to consider + include how to handle unknown charsets, any charsets that are + mandatory-to-implement, any issues with byte-order that might apply, + and any transfer encodings that need to be supported. + +5.2. Operations + + The protocol must specify which of the operations defined in this + specification (equality matching, substring matching, and ordering) + can be invoked in the protocol, and how they are invoked. There may + be more than one way to invoke an operation. + + The protocol MUST provide a mechanism for the client to select the + collation to use with equality matching, substring matching, and + ordering. + + If a protocol needs a total ordering and the collation chosen does + not provide it because the ordering operation returns "undefined" at + least once, the recommended fallback is to sort all invalid strings + after the valid ones, and use i;octet to order the invalid strings. + + Although the collation's substring function provides a list of + matches, a protocol need not provide all that to the client. It may + + + +Newman, et al. Standards Track [Page 11] + +RFC 4790 Collation Registry March 2007 + + + provide only the first matching substring, or even just the + information that the substring search matched. In this way, + collations can be used with protocols that are defined such that "x + is a substring of y" returns true-false. + + If the protocol provides positional information for the results of a + substring match, that positional information SHOULD fully specify the + substring(s) in the result that matches, independent of the length of + the search string. For example, returning both the starting and + ending offset of the match would suffice, as would the starting + offset and a length. Returning just the starting offset is not + acceptable. This rule is necessary because advanced collations can + treat strings of different lengths as equal (for example, pre- + composed and decomposed accented characters). + +5.3. Wildcards + + The protocol MUST specify whether it allows the use of wildcards in + collation identifiers. If the protocol allows wildcards, then: + The protocol MUST specify how comparisons behave in the absence of + explicit collation negotiation, or when a collation of "default" + is requested. The protocol MAY specify that the default collation + used in such circumstances is sensitive to server configuration. + + The protocol SHOULD provide a way to list available collations + matching a given wildcard pattern, or patterns. + +5.4. String Comparison + + If a protocol compares strings in any nontrivial way, using a + collation may be appropriate. As an example, many protocols use + case-independent strings. In many cases, a simple ASCII mapping to + upper/lower case works well. In other cases, it may be better to use + a specifiable collation; for example, so that a server can treat "i" + and "I" as equivalent in Italy, and different in Turkey (Turkish also + has a dotted upper-case" I" and a dotless lower-case "i"). + + Protocol designers should consider, in each case, whether to use a + specifiable collation. Keywords often have other needs than user + variables, and search arguments may be different again. + +5.5. Disconnected Clients + + If the protocol supports disconnected clients, and a collation is + used that can use configurable tables (e.g., to support + locale-specific extensions), then the client may not be able to + reproduce the server's collation operations while offline. + + + + +Newman, et al. Standards Track [Page 12] + +RFC 4790 Collation Registry March 2007 + + + A mechanism to download such tables has been discussed. Such a + mechanism is not included in the present specification, since the + problem is not yet well understood. + +5.6. Error Codes + + The protocol specification should consider assigning protocol error + codes for the following circumstances: + + o The client requests the use of a collation by identifier or + pattern, but no implemented collation matches that pattern. + + o The client attempts to use a collation for an operation that is + not supported by that collation -- for example, attempting to use + the "i;ascii-numeric" collation for substring matching. + + o The client uses an equality or substring matching collation, and + the result is an error. It may be appropriate to distinguish + between the two input strings, particularly when one is supplied + by the client and the other is stored by the server. It might + also be appropriate to distinguish the specific case of an invalid + UTF-8 string. + +5.7. Octet Collation + + The i;octet (Section 9.3) collation is only usable with protocols + based on octet-strings. Clients and servers MUST NOT use i;octet + with other protocols. + + If the protocol permits the use of collations with data structures + other than strings, the protocol MUST describe the default behavior + for a collation with those data structures. + +6. Use by Existing Protocols + + This section is informative. + + Both ACAP [11] and Sieve [14] are standards track specifications that + used collations prior to the creation of this specification and + registry. Those standards do not meet all the application protocol + requirements described in Section 5. + + These protocols allow the use of the i;octet (Section 9.3) collation + working directly on UTF-8 data, as used in these protocols. + + + + + + + +Newman, et al. Standards Track [Page 13] + +RFC 4790 Collation Registry March 2007 + + + In Sieve, all matches are either true or false. Accordingly, Sieve + servers must treat "undefined" and "no-match" results of the equality + and substring operations as false, and only "match" as true. + + In ACAP and Sieve, there are no invalid strings. In this document's + terms, invalid strings sort after valid strings. + + IMAP [15] also collates, although that is explicit only when the + COMPARATOR [17] extension is used. The built-in IMAP substring + operation and the ordering provided by the SORT [16] extension may + not meet the requirements made in this document. + + Other protocols may be in a similar position. + + In IMAP, the default collation is i;ascii-casemap, because its + operations are understood to match IMAP's built-in operations. + +7. Collation Registration + +7.1. Collation Registration Procedure + + The IETF will create a mailing list, collation@ietf.org, which can be + used for public discussion of collation proposals prior to + registration. Use of the mailing list is strongly encouraged. The + IESG will appoint a designated expert who will monitor the + collation@ietf.org mailing list and review registrations. + + The registration procedure begins when a completed registration + template is sent to iana@iana.org and collation@ietf.org. The + designated expert is expected to tell IANA and the submitter of the + registration within two weeks whether the registration is approved, + approved with minor changes, or rejected with cause. When a + registration is rejected with cause, it can be re-submitted if the + concerns listed in the cause are addressed. Decisions made by the + designated expert can be appealed to the IESG Applications Area + Director, then to the IESG. They follow the normal appeals procedure + for IESG decisions. + + Collation registrations in a standards track, BCP, or IESG-approved + experimental RFC are owned by the IETF, and changes to the + registration follow normal procedures for updating such documents. + Collation registrations in other RFCs are owned by the RFC author(s). + Other collation registrations are owned by the individual(s) listed + in the contact field of the registration, and IANA will preserve this + information. + + If the registration is a change of an existing collation, it MUST be + approved by the owner. In the event the owner cannot be contacted + + + +Newman, et al. Standards Track [Page 14] + +RFC 4790 Collation Registry March 2007 + + + for a period of one month, and the designated expert deems the change + necessary, the IESG MAY re-assign ownership to an appropriate party. + +7.2. Collation Registration Format + + Registration of a collation is done by sending a well-formed XML + document to collation@ietf.org and iana@iana.org. + +7.2.1. Registration Template + + Here is a template for the registration: + + <?xml version='1.0'?> + <!DOCTYPE collation SYSTEM 'collationreg.dtd'> + <collation rfc="YYYY" scope="global" intendedUse="common"> + <identifier>collation identifier</identifier> + <title>technical title for collation</title> + <operations>equality order substring</operations> + <specification>specification reference</specification> + <owner>email address of owner or IETF</owner> + <submitter>email address of submitter</submitter> + <version>1</version> + </collation> + +7.2.2. The Collation Element + + The root of the registration document MUST be a <collation> element. + The collation element contains the other elements in the + registration, which are described in the following sub-subsections, + in the order given here. + + The <collation> element MAY include an "rfc=" attribute if the + specification is in an RFC. The "rfc=" attribute gives only the + number of the RFC, without any prefix, such as "RFC", or suffix, such + as ".txt". + + The <collation> element MUST include a "scope=" attribute, which MUST + have one of the values "global", "local", or "other". + + The <collation> element MUST include an "intendedUse=" attribute, + which must have one of the values "common", "limited", "vendor", or + "deprecated". Collation specifications intended for "common" use are + expected to reference standards from standards bodies with + significant experience dealing with the details of international + character sets. + + Be aware that future revisions of this specification may add + additional function types, as well as additional XML attributes, + + + +Newman, et al. Standards Track [Page 15] + +RFC 4790 Collation Registry March 2007 + + + values, and elements. Any system that automatically parses these XML + documents MUST take this into account to preserve future + compatibility. + +7.2.3. The Identifier Element + + The <identifier> element gives the precise identifier of the + collation, e.g., i;ascii-casemap. The <identifier> element is + mandatory. + +7.2.4. The Title Element + + The <title> element gives the title of the collation. The <title> + element is mandatory. + +7.2.5. The Operations Element + + The <operations> element lists which of the three operations + ("equality", "order" or "substring") the collation provides, + separated by single spaces. The <operations> element is mandatory. + +7.2.6. The Specification Element + + The <specification> element describes where to find the + specification. The <specification> element is mandatory. It MAY + have a URI attribute. There may be more than one <specification> + element, in which case, they together form the specification. + + If it is discovered that parts of a collation specification conflict, + a new revision of the collation is necessary, and the + collation@ietf.org mailing list should be notified. + +7.2.7. The Submitter Element + + The <submitter> element provides an RFC 2822 [12] email address for + the person who submitted the registration. It is optional if the + <owner> element contains an email address. + + There may be more than one <submitter> element. + +7.2.8. The Owner Element + + The <owner> element contains either the four letters "IETF" or an + email address of the owner of the registration. The <owner> element + is mandatory. There may be more than one <owner> element. If so, + all owners are equal. Each owner can speak for all. + + + + + +Newman, et al. Standards Track [Page 16] + +RFC 4790 Collation Registry March 2007 + + +7.2.9. The Version Element + + The <version> element MUST be included when the registration is + likely to be revised, or has been revised in such a way that the + results change for one or more input strings. The <version> element + is optional. + +7.2.10. The Variable Element + + The <variable> element specifies an optional variable to control the + collation's behaviour, for example whether it is case sensitive. The + <variable> element is optional. When <variable> is used, it must + contain <name> and <default> elements, and it may contain one or more + <value> elements. + +7.2.10.1. The Name Element + + The <name> element specifies the name value of a variable. The + <name> element is mandatory. + +7.2.10.2. The Default Element + + The <default> element specifies the default value of a variable. The + <default> element is mandatory. + +7.2.10.3. The Value Element + + The <value> element specifies a legal value of a variable. The + <value> element is optional. If one or more <value> elements are + present, only those values are legal. If none are, then the + variable's legal values do not form an enumerated set, and the rules + MUST be specified in an RFC accompanying the registration. + +7.3. Structure of Collation Registry + + Once the registration is approved, IANA will store each XML + registration document in a URL of the form + http://www.iana.org/assignments/collation/collation-id.xml, where + collation-id is the content of the identifier element in the + registration. Both the submitter and the designated expert are + responsible for verifying that the XML is well-formed. The + registration document should avoid using new elements. If any are + necessary, it is important to be consistent with other registrations. + + IANA will also maintain a text summary of the registry under the name + http://www.iana.org/assignments/collation/collation-index.html. This + summary is divided into four sections. The first section is for + collations intended for common use. This section is intended for + + + +Newman, et al. Standards Track [Page 17] + +RFC 4790 Collation Registry March 2007 + + + collation registrations published in IESG-approved RFCs, or for + locally scoped collations from the primary standards body for that + locale. The designated expert is encouraged to reject collation + registrations with an intended use of "common" if the expert believes + it should be "limited", as it is desirable to keep the number of + "common" registrations small and of high quality. The second section + is reserved for limited-use collations. The third section is + reserved for registered vendor-specific collations. The final + section is reserved for deprecated collations. + +7.4. Example Initial Registry Summary + + The following is an example of how IANA might structure the initial + registry summary.html file: + + Collation Functions Scope Reference + --------- --------- ----- --------- + Common Use Collations: + i;ascii-casemap e, o, s Local [RFC 4790] + + Limited Use Collations: + i;octet e, o, s Other [RFC 4790] + i;ascii-numeric e, o Other [RFC 4790] + + Vendor Collations: + + Deprecated Collations: + + + References + ---------- + [RFC 4790] Newman, C., Duerst, M., Gulbrandsen, A., "Internet + Application Protocol Collation Registry", RFC 4790, + Sun Microsystems, March 2007. + +8. Guidelines for Expert Reviewer + + The expert reviewer appointed by the IESG has fairly broad latitude + for this registry. While a number of collations are expected + (particularly customizations of the UCA for localized use), an + explosion of collations (particularly common-use collations) is not + desirable for widespread interoperability. However, it is important + for the expert reviewer to provide cause when rejecting a + registration, and, when possible, to describe corrective action to + + + + + + + +Newman, et al. Standards Track [Page 18] + +RFC 4790 Collation Registry March 2007 + + + permit the registration to proceed. The following table includes + some example reasons to reject a registration with cause: + + o The registration is not a well-formed XML document. + + o The registration has an intended use of "common", but there is no + evidence the collation will be widely deployed, so it should be + listed as "limited". + + o The registration has an intended use of "common", but it is + redundant with the functionality of a previously registered + "common" collation. + + o The registration has an intended use of "common", but the + specification is not detailed enough to allow interoperable + implementations by others. + + o The collation identifier fails to precisely identify the version + numbers of relevant tables to use. + + o The registration fails to meet one of the "MUST" requirements in + Section 4. + + o The collation identifier fails to meet the syntax in Section 3. + + o The collation specification referenced in the registration is + vague or has optional features without a clear behavior specified. + + o The referenced specification does not adequately address security + considerations specific to that collation. + + o The registration's operations are needlessly different from those + of traditional operations. + + o The registration's XML is needlessly different from that of + already registered collations. + +9. Initial Collations + + This section registers the three collations that were originally + defined in [11], and are implemented in most [14] engines. Some of + the behavior of these collations is perhaps not ideal, such as + i;ascii-casemap accepting non-ASCII input. Compatibility with widely + deployed code was judged more important than fixing the collations. + Some of the aspects of these collations are necessary to maintain + compatibility with widely deployed code. + + + + + +Newman, et al. Standards Track [Page 19] + +RFC 4790 Collation Registry March 2007 + + +9.1. ASCII Numeric Collation + +9.1.1. ASCII Numeric Collation Description + + The "i;ascii-numeric" collation is a simple collation intended for + use with arbitrarily-sized, unsigned decimal integer numbers stored + as octet strings. US-ASCII digits (0x30 to 0x39) represent digits of + the numbers. Before converting from string to integer, the input + string is truncated at the first non-digit character. All input is + valid; strings that do not start with a digit represent positive + infinity. + + The collation supports equality and ordering, but does not support + the substring operation. + + The equality operation returns "match" if the two strings represent + the same number (i.e., leading zeroes and trailing non-digits are + disregarded), and "no-match" if the two strings represent different + numbers. + + The ordering operation returns "less" if the first string represents + a smaller number than the second, "equal" if they represent the same + number, and "greater" if the first string represents a larger number + than the second. + + Some examples: "0" is less than "1", and "1" is less than + "4294967298". "4294967298", "04294967298", and "4294967298b" are all + equal. "04294967298" is less than "". "", "x", and "y" are equal. + +9.1.2. ASCII Numeric Collation Registration + + <?xml version='1.0'?> + <!DOCTYPE collation SYSTEM 'collationreg.dtd'> + <collation rfc="4790" scope="other" intendedUse="limited"> + <identifier>i;ascii-numeric</identifier> + <title>ASCII Numeric</title> + <operations>equality order</operations> + <specification>RFC 4790</specification> + <owner>IETF</owner> + <submitter>chris.newman@sun.com</submitter> + </collation> + + + + + + + + + + +Newman, et al. Standards Track [Page 20] + +RFC 4790 Collation Registry March 2007 + + +9.2. ASCII Casemap Collation + +9.2.1. ASCII Casemap Collation Description + + The "i;ascii-casemap" collation is a simple collation that operates + on octet strings and treats US-ASCII letters case-insensitively. It + provides equality, substring, and ordering operations. All input is + valid. Note that letters outside ASCII are not treated case- + insensitively. + + Its equality, ordering, and substring operations are as for i;octet, + except that at first, the lower-case letters (octet values 97-122) in + each input string are changed to upper case (octet values 65-90). + + Care should be taken when using OS-supplied functions to implement + this collation, as it is not locale sensitive. Functions, such as + strcasecmp and toupper, are sometimes locale sensitive, and may + inappropriately map lower-case letters other than a-z to upper case. + + The i;ascii-casemap collation is well-suited for use with many + Internet protocols and computer languages. Use with natural language + is often inappropriate; even though the collation apparently supports + languages such as Swahili and English, in real-world use, it tends to + mis-sort a number of types of string: + + o people and place names containing non-ASCII, + + o words such as "naive" (if spelled with an accent, the accented + character could push the word to the wrong spot in a sorted list), + + o names such as "Lloyd" (which, in Welsh, sorts after "Lyon", unlike + in English), + + o strings containing euro and pound sterling symbols, quotation + marks other than '"', dashes/hyphens, etc. + + + + + + + + + + + + + + + + +Newman, et al. Standards Track [Page 21] + +RFC 4790 Collation Registry March 2007 + + +9.2.2. ASCII Casemap Collation Registration + + <?xml version='1.0'?> + <!DOCTYPE collation SYSTEM 'collationreg.dtd'> + <collation rfc="4790" scope="local" intendedUse="common"> + <identifier>i;ascii-casemap</identifier> + <title>ASCII Casemap</title> + <operations>equality order substring</operations> + <specification>RFC 4790</specification> + <owner>IETF</owner> + <submitter>chris.newman@sun.com</submitter> + </collation> + +9.3. Octet Collation + +9.3.1. Octet Collation Description + + The "i;octet" collation is a simple and fast collation intended for + use on binary octet strings rather than on character data. Protocols + that want to make this collation available have to do so by + explicitly allowing it. If not explicitly allowed, it MUST NOT be + used. It never returns an "undefined" result. It provides equality, + substring, and ordering operations. + + The ordering algorithm is as follows: + + 1. If both strings are the empty string, return the result "equal". + + 2. If the first string is empty and the second is not, return the + result "less". + + 3. If the second string is empty and the first is not, return the + result "greater". + + 4. If both strings begin with the same octet value, remove the first + octet from both strings and repeat this algorithm from step 1. + + 5. If the unsigned value (0 to 255) of the first octet of the first + string is less than the unsigned value of the first octet of the + second string, then return "less". + + 6. If this step is reached, return "greater". + + This algorithm is roughly equivalent to the C library function + memcmp, with appropriate length checks added. + + + + + + +Newman, et al. Standards Track [Page 22] + +RFC 4790 Collation Registry March 2007 + + + The matching operation returns "match" if the sorting algorithm would + return "equal". Otherwise, the matching operation returns "no- + match". + + The substring operation returns "match" if the first string is the + empty string, or if there exists a substring of the second string of + length equal to the length of the first string, which would result in + a "match" result from the equality function. Otherwise, the + substring operation returns "no-match". + +9.3.2. Octet Collation Registration + + This collation is defined with intendedUse="limited" because it can + only be used by protocols that explicitly allow it. + + <?xml version='1.0'?> + <!DOCTYPE collation SYSTEM 'collationreg.dtd'> + <collation rfc="4790" scope="global" intendedUse="limited"> + <identifier>i;octet</identifier> + <title>Octet</title> + <operations>equality order substring</operations> + <specification>RFC 4790</specification> + <owner>IETF</owner> + <submitter>chris.newman@sun.com</submitter> + </collation> + +10. IANA Considerations + + Section 7 defines how to register collations with IANA. Section 9 + defines a list of predefined collations that have been registered + with IANA. + +11. Security Considerations + + Collations will normally be used with UTF-8 strings. Thus, the + security considerations for UTF-8 [3], stringprep [6], and Unicode + TR-36 [8] also apply, and are normative to this specification. + +12. Acknowledgements + + The authors want to thank all who have contributed to this document, + including Brian Carpenter, John Cowan, Dave Cridland, Mark Davis, + Spencer Dawkins, Lisa Dusseault, Lars Eggert, Frank Ellermann, Philip + Guenther, Tony Hansen, Ted Hardie, Sam Hartman, Kjetil Torgrim Homme, + Michael Kay, John Klensin, Alexey Melnikov, Jim Melton, and Abhijit + Menon-Sen. + + + + + +Newman, et al. Standards Track [Page 23] + +RFC 4790 Collation Registry March 2007 + + +13. References + +13.1. Normative References + + [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement + Levels", BCP 14, RFC 2119, March 1997. + + [2] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 4234, October 2005. + + [3] Yergeau, F., "UTF-8, a transformation format of ISO 10646", + STD 63, RFC 3629, November 2003. + + [4] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform + Resource Identifier (URI): Generic Syntax", RFC 3986, + January 2005. + + [5] Phillips, A. and M. Davis, "Tags for Identifying Languages", + BCP 47, RFC 4646, September 2006. + + [6] Hoffman, P. and M. Blanchet, "Preparation of Internationalized + Strings ("stringprep")", RFC 3454, December 2002. + + [7] Davis, M. and K. Whistler, "Unicode Collation Algorithm version + 14", May 2005, + <http://www.unicode.org/reports/tr10/tr10-14.html>. + + [8] Davis, M. and M. Suignard, "Unicode Security Considerations", + February 2006, <http://www.unicode.org/reports/tr36/>. + +13.2. Informative References + + [9] Freed, N. and N. Borenstein, "Multipurpose Internet Mail + Extensions (MIME) Part One: Format of Internet Message Bodies", + RFC 2045, November 1996. + + [10] Melnikov, A., "Simple Authentication and Security Layer + (SASL)", RFC 4422, June 2006. + + [11] Newman, C. and J. Myers, "ACAP -- Application Configuration + Access Protocol", RFC 2244, November 1997. + + [12] Resnick, P., "Internet Message Format", RFC 2822, April 2001. + + [13] Freed, N. and J. Postel, "IANA Charset Registration + Procedures", BCP 19, RFC 2978, October 2000. + + + + + +Newman, et al. Standards Track [Page 24] + +RFC 4790 Collation Registry March 2007 + + + [14] Showalter, T., "Sieve: A Mail Filtering Language", RFC 3028, + January 2001. + + [15] Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 3501, March 2003. + + [16] Crispin, M. and K. Murchison, "Internet Message Access Protocol + - Sort and Thread Extensions", Work in Progress, May 2004. + + [17] Newman, C. and A. Gulbrandsen, "Internet Message Access + Protocol Internationalization", Work in Progress, January 2006. + +Authors' Addresses + + Chris Newman + Sun Microsystems + 1050 Lakes Drive + West Covina, CA 91790 + USA + + EMail: chris.newman@sun.com + + + Martin Duerst + Aoyama Gakuin University + 5-10-1 Fuchinobe + Sagamihara, Kanagawa 229-8558 + Japan + + Phone: +81 42 759 6329 + Fax: +81 42 759 6495 + EMail: duerst@it.aoyama.ac.jp + URI: http://www.sw.it.aoyama.ac.jp/D%C3%BCrst/ + + Note: Please write "Duerst" with u-umlaut wherever possible, for + example as "Dürst" in XML and HTML. + + + Arnt Gulbrandsen + Oryx Mail Systems GmbH + Schweppermannstr. 8 + 81671 Munich + Germany + + Fax: +49 89 4502 9758 + EMail: arnt@oryx.com + URI: http://www.oryx.com/arnt/ + + + + +Newman, et al. Standards Track [Page 25] + +RFC 4790 Collation Registry March 2007 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2007). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + +Newman, et al. Standards Track [Page 26] + diff --git a/imap/docs/rfc/rfc4959.txt b/imap/docs/rfc/rfc4959.txt new file mode 100644 index 00000000..3df18354 --- /dev/null +++ b/imap/docs/rfc/rfc4959.txt @@ -0,0 +1,395 @@ + + + + + + +Network Working Group R. Siemborski +Request for Comments: 4959 Google, Inc. +Category: Standards Track A. Gulbrandsen + Oryx Mail Systems GmbH + September 2007 + + + IMAP Extension for Simple Authentication and Security Layer (SASL) + Initial Client Response + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + To date, the Internet Message Access Protocol (IMAP) has used a + Simple Authentication and Security Layer (SASL) profile which always + required at least one complete round trip for an authentication, as + it did not support an initial client response argument. This + additional round trip at the beginning of the session is undesirable, + especially when round-trip costs are high. + + This document defines an extension to IMAP which allows clients and + servers to avoid this round trip by allowing an initial client + response argument to the IMAP AUTHENTICATE command. + + + + + + + + + + + + + + + + + + + + + +Siemborski & Gulbrandsen Standards Track [Page 1] + +RFC 4959 IMAP Ext for SASL Initial Client Response September 2007 + + +1. Introduction + + The SASL initial client response extension is present in any IMAP + [RFC3501] server implementation which returns "SASL-IR" as one of the + supported capabilities in its CAPABILITY response. + + Servers which support this extension will accept an optional initial + client response with the AUTHENTICATE command for any SASL [RFC4422] + mechanisms which support it. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. + + Formal syntax is defined by [RFC4234] as extended by [RFC3501]. + +3. IMAP Changes to the IMAP AUTHENTICATE Command + + This extension adds an optional second argument to the AUTHENTICATE + command that is defined in Section 6.2.2 of [RFC3501]. If this + second argument is present, it represents the contents of the + "initial client response" defined in Section 5.1 of [RFC4422]. + + As with any other client response, this initial client response MUST + be encoded as defined in Section 4 of [RFC4648]. It also MUST be + transmitted outside of a quoted string or literal. To send a zero- + length initial response, the client MUST send a single pad character + ("="). This indicates that the response is present, but is a zero- + length string. + + When decoding the BASE64 [RFC4648] data in the initial client + response, decoding errors MUST be treated as IMAP [RFC3501] would + handle them in any normal SASL client response. In particular, the + server should check for any characters not explicitly allowed by the + BASE64 alphabet, as well as any sequence of BASE64 characters that + contains the pad character ('=') anywhere other than the end of the + string (e.g., "=AAA" and "AAA=BBB" are not allowed). + + If the client uses an initial response with a SASL mechanism that + does not support an initial response, the server MUST reject the + command with a tagged BAD response. + + + + + +Siemborski & Gulbrandsen Standards Track [Page 2] + +RFC 4959 IMAP Ext for SASL Initial Client Response September 2007 + + + Note: support and use of the initial client response is optional for + both clients and servers. Servers that implement this extension MUST + support clients that omit the initial client response, and clients + that implement this extension MUST NOT send an initial client + response to servers that do not advertise the SASL-IR capability. In + such a situation, clients MUST fall back to an IMAP [RFC3501] + compatible mode. + + If either the client or the server do not support the SASL-IR + capability, a mechanism which uses an initial client response is + negotiated using the challenge/response exchange described in + [RFC3501], with an initial zero-length server challenge. + +4. Examples + + The following is an example authentication using the PLAIN (see + [RFC4616]) SASL mechanism (under a TLS protection layer, see + [RFC4346]) and an initial client response: + + ... client connects to server and negotiates a TLS + protection layer ... + C: C01 CAPABILITY + S: * CAPABILITY IMAP4rev1 SASL-IR AUTH=PLAIN + S: C01 OK Completed + C: A01 AUTHENTICATE PLAIN dGVzdAB0ZXN0AHRlc3Q= + S: A01 OK Success (tls protection) + + Note that even when a server supports this extension, the following + negotiation (which does not use the initial response) is still valid + and MUST be supported by the server: + + ... client connects to server and negotiates a TLS + protection layer ... + C: C01 CAPABILITY + S: * CAPABILITY IMAP4rev1 SASL-IR AUTH=PLAIN + S: C01 OK Completed + C: A01 AUTHENTICATE PLAIN + (note that there is a space following the "+" in the + following line) + S: + + C: dGVzdAB0ZXN0AHRlc3Q= + S: A01 OK Success (tls protection) + + The following is an example authentication using the SASL EXTERNAL + mechanism (defined in [RFC4422]) under a TLS protection layer (see + [RFC4346]) and an empty initial client response: + + + + + +Siemborski & Gulbrandsen Standards Track [Page 3] + +RFC 4959 IMAP Ext for SASL Initial Client Response September 2007 + + + ... client connects to server and negotiates a TLS + protection layer ... + C: C01 CAPABILITY + S: * CAPABILITY IMAP4rev1 SASL-IR AUTH=PLAIN AUTH=EXTERNAL + S: C01 OK Completed + C: A01 AUTHENTICATE EXTERNAL = + S: A01 OK Success (tls protection) + + This is in contrast with the handling of such a situation when an + initial response is omitted: + + ... client connects to server and negotiates a TLS protection + layer ... + C: C01 CAPABILITY + S: * CAPABILITY IMAP4rev1 SASL-IR AUTH=PLAIN AUTH=EXTERNAL + S: C01 OK Completed + C: A01 AUTHENTICATE EXTERNAL + (note that there is a space following the "+" in the + following line) + S: + + C: + S: A01 OK Success (tls protection) + +5. IANA Considerations + + The IANA has added SASL-IR to the IMAP4 Capabilities Registry. + +6. Security Considerations + + The extension defined in this document is subject to many of the + Security Considerations defined in [RFC3501] and [RFC4422]. + + Server implementations MUST treat the omission of an initial client + response from the AUTHENTICATE command as defined by [RFC3501] (as if + this extension did not exist). + + Although [RFC3501] has no express line length limitations, some + implementations choose to enforce them anyway. Such implementations + MUST be aware that the addition of the initial response parameter to + AUTHENTICATE may increase the maximum line length that IMAP parsers + may expect to support. Server implementations MUST be able to + receive the largest possible initial client response that their + supported mechanisms might receive. + + + + + + + + +Siemborski & Gulbrandsen Standards Track [Page 4] + +RFC 4959 IMAP Ext for SASL Initial Client Response September 2007 + + +7. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form [RFC4234] notation. [RFC3501] defines the non-terminals + capability, auth-type, and base64. + + capability =/ "SASL-IR" + + authenticate = "AUTHENTICATE" SP auth-type [SP (base64 / "=")] + *(CRLF base64) + ;;redefine AUTHENTICATE from [RFC3501] + +8. Acknowledgments + + The authors would like to acknowledge the contributions of Ken + Murchison and Mark Crispin, along with the rest of the IMAPEXT + Working Group for their assistance in reviewing this document. + + Alexey Melnikov and Cyrus Daboo also had some early discussions about + this extension. + +9. References + +9.1. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 4234, October 2005. + + [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and + Security Layer (SASL)", RFC 4422, June 2006. + + [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data + Encodings", RFC 4648, October 2006. + +9.2. Informative References + + [RFC4616] Zeilenga, K., "The PLAIN Simple Authentication and + Security Layer (SASL) Mechanism", RFC 4616, August 2006. + + [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security + (TLS) Protocol Version 1.1", RFC 4346, April 2006. + + + + +Siemborski & Gulbrandsen Standards Track [Page 5] + +RFC 4959 IMAP Ext for SASL Initial Client Response September 2007 + + +Authors' Addresses + + Robert Siemborski + Google, Inc. + 1600 Ampitheatre Parkway + Mountain View, CA 94043 + + Phone: +1 650 623 6925 + EMail: robsiemb@google.com + + + Arnt Gulbrandsen + Oryx Mail Systems GmbH + Schweppermannstr. 8 + D-81671 Muenchen + Germany + + EMail: arnt@oryx.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Siemborski & Gulbrandsen Standards Track [Page 6] + +RFC 4959 IMAP Ext for SASL Initial Client Response September 2007 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2007). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Siemborski & Gulbrandsen Standards Track [Page 7] + diff --git a/imap/docs/rfc/rfc4978.txt b/imap/docs/rfc/rfc4978.txt new file mode 100644 index 00000000..14b56b6e --- /dev/null +++ b/imap/docs/rfc/rfc4978.txt @@ -0,0 +1,507 @@ + + + + + + +Network Working Group A. Gulbrandsen +Request for Comments: 4978 Oryx Mail Systems GmbH +Category: Standards Track August 2007 + + + The IMAP COMPRESS Extension + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + The COMPRESS extension allows an IMAP connection to be effectively + and efficiently compressed. + + Table of Contents + + 1. Introduction and Overview .......................................2 + 2. Conventions Used in This Document ...............................2 + 3. The COMPRESS Command ............................................3 + 4. Compression Efficiency ..........................................4 + 5. Formal Syntax ...................................................6 + 6. Security Considerations .........................................6 + 7. IANA Considerations .............................................6 + 8. Acknowledgements ................................................7 + 9. References ......................................................7 + 9.1. Normative References .......................................7 + 9.2. Informative References .....................................7 + + + + + + + + + + + + + + + + + + +Gulbrandsen Standards Track [Page 1] + +RFC 4978 The IMAP COMPRESS Extension August 2007 + + +1. Introduction and Overview + + A server which supports the COMPRESS extension indicates this with + one or more capability names consisting of "COMPRESS=" followed by a + supported compression algorithm name as described in this document. + + The goal of COMPRESS is to reduce the bandwidth usage of IMAP. + + Compared to PPP compression (see [RFC1962]) and modem-based + compression (see [MNP] and [V42BIS]), COMPRESS offers much better + compression efficiency. COMPRESS can be used together with Transport + Security Layer (TLS) [RFC4346], Simple Authentication and Security + layer (SASL) encryption, Virtual Private Networks (VPNs), etc. + Compared to TLS compression [RFC3749], COMPRESS has the following + (dis)advantages: + + - COMPRESS can be implemented easily both by IMAP servers and + clients. + + - IMAP COMPRESS benefits from an intimate knowledge of the IMAP + protocol's state machine, allowing for dynamic and aggressive + optimization of the underlying compression algorithm's parameters. + + - When the TLS layer implements compression, any protocol using that + layer can transparently benefit from that compression (e.g., SMTP + and IMAP). COMPRESS is specific to IMAP. + + In order to increase interoperation, it is desirable to have as few + different compression algorithms as possible, so this document + specifies only one. The DEFLATE algorithm (defined in [RFC1951]) is + standard, widely available and fairly efficient, so it is the only + algorithm defined by this document. + + In order to increase interoperation, IMAP servers that advertise this + extension SHOULD also advertise the TLS DEFLATE compression mechanism + as defined in [RFC3749]. IMAP clients MAY use either COMPRESS or TLS + compression, however, if the client and server support both, it is + RECOMMENDED that the client choose TLS compression. + + The extension adds one new command (COMPRESS) and no new responses. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + + Formal syntax is defined by [RFC4234] as modified by [RFC3501]. + + + +Gulbrandsen Standards Track [Page 2] + +RFC 4978 The IMAP COMPRESS Extension August 2007 + + + In the examples, "C:" and "S:" indicate lines sent by the client and + server respectively. "[...]" denotes elision. + +3. The COMPRESS Command + + Arguments: Name of compression mechanism: "DEFLATE". + + Responses: None + + Result: OK The server will compress its responses and expects the + client to compress its commands. + NO Compression is already active via another layer. + BAD Command unknown, invalid or unknown argument, or COMPRESS + already active. + + The COMPRESS command instructs the server to use the named + compression mechanism ("DEFLATE" is the only one defined) for all + commands and/or responses after COMPRESS. + + The client MUST NOT send any further commands until it has seen the + result of COMPRESS. If the response was OK, the client MUST compress + starting with the first command after COMPRESS. If the server + response was BAD or NO, the client MUST NOT turn on compression. + + If the server responds NO because it knows that the same mechanism is + active already (e.g., because TLS has negotiated the same mechanism), + it MUST send COMPRESSIONACTIVE as resp-text-code (see [RFC3501], + Section 7.1), and the resp-text SHOULD say which layer compresses. + + If the server issues an OK response, the server MUST compress + starting immediately after the CRLF which ends the tagged OK + response. (Responses issued by the server before the OK response + will, of course, still be uncompressed.) If the server issues a BAD + or NO response, the server MUST NOT turn on compression. + + For DEFLATE (as for many other compression mechanisms), the + compressor can trade speed against quality. When decompressing there + isn't much of a tradeoff. Consequently, the client and server are + both free to pick the best reasonable rate of compression for the + data they send. + + When COMPRESS is combined with TLS (see [RFC4346]) or SASL (see + [RFC4422]) security layers, the sending order of the three extensions + MUST be first COMPRESS, then SASL, and finally TLS. That is, before + data is transmitted it is first compressed. Second, if a SASL + security layer has been negotiated, the compressed data is then + signed and/or encrypted accordingly. Third, if a TLS security layer + has been negotiated, the data from the previous step is signed and/or + + + +Gulbrandsen Standards Track [Page 3] + +RFC 4978 The IMAP COMPRESS Extension August 2007 + + + encrypted accordingly. When receiving data, the processing order + MUST be reversed. This ensures that before sending, data is + compressed before it is encrypted, independent of the order in which + the client issues COMPRESS, AUTHENTICATE, and STARTTLS. + + The following example illustrates how commands and responses are + compressed during a simple login sequence: + + S: * OK [CAPABILITY IMAP4REV1 STARTTLS COMPRESS=DEFLATE] + C: a starttls + S: a OK TLS active + + From this point on, everything is encrypted. + + C: b login arnt tnra + S: b OK Logged in as arnt + C: c compress deflate + S: d OK DEFLATE active + + From this point on, everything is compressed before being + encrypted. + + The following example demonstrates how a server may refuse to + compress twice: + + S: * OK [CAPABILITY IMAP4REV1 STARTTLS COMPRESS=DEFLATE] + [...] + C: c compress deflate + S: c NO [COMPRESSIONACTIVE] DEFLATE active via TLS + +4. Compression Efficiency + + This section is informative, not normative. + + IMAP poses some unusual problems for a compression layer. + + Upstream is fairly simple. Most IMAP clients send the same few + commands again and again, so any compression algorithm that can + exploit repetition works efficiently. The APPEND command is an + exception; clients that send many APPEND commands may want to + surround large literals with flushes in the same way as is + recommended for servers later in this section. + + Downstream has the unusual property that several kinds of data are + sent, confusing all dictionary-based compression algorithms. + + + + + + +Gulbrandsen Standards Track [Page 4] + +RFC 4978 The IMAP COMPRESS Extension August 2007 + + + One type is IMAP responses. These are highly compressible; zlib + using its least CPU-intensive setting compresses typical responses to + 25-40% of their original size. + + Another type is email headers. These are equally compressible, and + benefit from using the same dictionary as the IMAP responses. + + A third type is email body text. Text is usually fairly short and + includes much ASCII, so the same compression dictionary will do a + good job here, too. When multiple messages in the same thread are + read at the same time, quoted lines etc. can often be compressed + almost to zero. + + Finally, attachments (non-text email bodies) are transmitted, either + in binary form or encoded with base-64. + + When attachments are retrieved in binary form, DEFLATE may be able to + compress them, but the format of the attachment is usually not IMAP- + like, so the dictionary built while compressing IMAP does not help. + The compressor has to adapt its dictionary from IMAP to the + attachment's format, and then back. A few file formats aren't + compressible at all using deflate, e.g., .gz, .zip, and .jpg files. + + When attachments are retrieved in base-64 form, the same problems + apply, but the base-64 encoding adds another problem. 8-bit + compression algorithms such as deflate work well on 8-bit file + formats, however base-64 turns a file into something resembling 6-bit + bytes, hiding most of the 8-bit file format from the compressor. + + When using the zlib library (see [RFC1951]), the functions + deflateInit2(), deflate(), inflateInit2(), and inflate() suffice to + implement this extension. The windowBits value must be in the range + -8 to -15, or else deflateInit2() uses the wrong format. + deflateParams() can be used to improve compression rate and resource + use. The Z_FULL_FLUSH argument to deflate() can be used to clear the + dictionary (the receiving peer does not need to do anything). + + A client can improve downstream compression by implementing BINARY + (defined in [RFC3516]) and using FETCH BINARY instead of FETCH BODY. + In the author's experience, the improvement ranges from 5% to 40% + depending on the attachment being downloaded. + + A server can improve downstream compression if it hints to the + compressor that the data type is about to change strongly, e.g., by + sending a Z_FULL_FLUSH at the start and end of large non-text + literals (before and after '*CHAR8' in the definition of literal in + RFC 3501, page 86). Small literals are best left alone. A possible + boundary is 5k. + + + +Gulbrandsen Standards Track [Page 5] + +RFC 4978 The IMAP COMPRESS Extension August 2007 + + + A server can improve the CPU efficiency both of the server and the + client if it adjusts the compression level (e.g., using the + deflateParams() function in zlib) at these points, to avoid trying to + compress incompressible attachments. A very simple strategy is to + change the level to 0 at the start of a literal provided the first + two bytes are either 0x1F 0x8B (as in deflate-compressed files) or + 0xFF 0xD8 (JPEG), and to keep it at 1-5 the rest of the time. More + complex strategies are possible. + +5. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [RFC4234]. This syntax augments + the grammar specified in [RFC3501]. [RFC4234] defines SP and + [RFC3501] defines command-auth, capability, and resp-text-code. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper or lower case characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + command-auth =/ compress + + compress = "COMPRESS" SP algorithm + + capability =/ "COMPRESS=" algorithm + ;; multiple COMPRESS capabilities allowed + + algorithm = "DEFLATE" + + resp-text-code =/ "COMPRESSIONACTIVE" + + Note that due the syntax of capability names, future algorithm names + must be atoms. + +6. Security Considerations + + As for TLS compression [RFC3749]. + +7. IANA Considerations + + The IANA has added COMPRESS=DEFLATE to the list of IMAP capabilities. + + + + + + + + + +Gulbrandsen Standards Track [Page 6] + +RFC 4978 The IMAP COMPRESS Extension August 2007 + + +8. Acknowledgements + + Eric Burger, Dave Cridland, Tony Finch, Ned Freed, Philip Guenther, + Randall Gellens, Tony Hansen, Cullen Jennings, Stephane Maes, Alexey + Melnikov, Lyndon Nerenberg, and Zoltan Ordogh have all helped with + this document. + + The author would also like to thank various people in the rooms at + meetings, whose help is real, but not reflected in the author's + mailbox. + +9. References + +9.1. Normative References + + [RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification + version 1.3", RFC 1951, May 1996. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 4234, October 2005. + +9.2. Informative References + + [RFC1962] Rand, D., "The PPP Compression Control Protocol (CCP)", + RFC 1962, June 1996. + + [RFC3516] Nerenberg, L., "IMAP4 Binary Content Extension", RFC 3516, + April 2003. + + [RFC3749] Hollenbeck, S., "Transport Layer Security Protocol + Compression Methods", RFC 3749, May 2004. + + [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security + (TLS) Protocol Version 1.1", RFC 4346, April 2006. + + [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and + Security Layer (SASL)", RFC 4422, June 2006. + + [V42BIS] ITU, "V.42bis: Data compression procedures for data + circuit-terminating equipment (DCE) using error correction + procedures", http://www.itu.int/rec/T-REC-V.42bis, January + 1990. + + + +Gulbrandsen Standards Track [Page 7] + +RFC 4978 The IMAP COMPRESS Extension August 2007 + + + [MNP] Gilbert Held, "The Complete Modem Reference", Second + Edition, Wiley Professional Computing, ISBN 0-471-00852-4, + May 1994. + +Author's Address + + Arnt Gulbrandsen + Oryx Mail Systems GmbH + Schweppermannstr. 8 + D-81671 Muenchen + Germany + + Fax: +49 89 4502 9758 + EMail: arnt@oryx.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Gulbrandsen Standards Track [Page 8] + +RFC 4978 The IMAP COMPRESS Extension August 2007 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2007). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Gulbrandsen Standards Track [Page 9] + diff --git a/imap/docs/rfc/rfc5032.txt b/imap/docs/rfc/rfc5032.txt new file mode 100644 index 00000000..f8e48953 --- /dev/null +++ b/imap/docs/rfc/rfc5032.txt @@ -0,0 +1,283 @@ + + + + + + +Network Working Group E. Burger, Ed. +Request for Comments: 5032 BEA Systems, Inc. +Updates: 3501 September 2007 +Category: Standards Track + + + WITHIN Search Extension to the IMAP Protocol + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + This document describes the WITHIN extension to IMAP SEARCH. IMAP + SEARCH returns messages whose internal date is within or outside a + specified interval. The mechanism described here, OLDER and YOUNGER, + differs from BEFORE and SINCE in that the client specifies an + interval, rather than a date. WITHIN is useful for persistent + searches where either the device does not have the capacity to + perform the search at regular intervals or the network is of limited + bandwidth and thus there is a desire to reduce network traffic from + sending repeated requests and redundant responses. + +1. Introduction + + This extension exposes two new search keys, OLDER and YOUNGER, each + of which takes a non-zero integer argument corresponding to a time + interval in seconds. The server calculates the time of interest by + subtracting the time interval the client presents from the current + date and time of the server. The server then either returns messages + older or younger than the resultant time and date, depending on the + search key used. + +1.1. Conventions Used in This Document + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [RFC2119]. + + + + + +Burger Standards Track [Page 1] + +RFC 5032 Search Within September 2007 + + + When describing the general syntax, we omit some definitions, as RFC + 3501 [RFC3501] defines them. + +2. Protocol Operation + + An IMAP4 server that supports the capability described here MUST + return "WITHIN" as one of the server supported capabilities in the + CAPABILITY command. + + For both the OLDER and YOUNGER search keys, the server calculates a + target date and time by subtracting the interval, specified in + seconds, from the current date and time of the server. The server + then compares the target time with the INTERNALDATE of the message, + as specified in IMAP [RFC3501]. For OLDER, messages match if the + INTERNALDATE is less recent than or equal to the target time. For + YOUNGER, messages match if the INTERNALDATE is more recent than or + equal to the target time. + + Both OLDER and YOUNGER searches always result in exact matching, to + the resolution of a second. However, if one is doing a dynamic + evaluation, for example, in a context [CONTEXT], one needs to be + aware that the server might perform the evaluation periodically. + Thus, the server may delay the updates. Clients MUST be aware that + dynamic search results may not reflect the current state of the + mailbox. If the client needs a search result that reflects the + current state of the mailbox, we RECOMMEND that the client issue a + new search. + +3. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation. Elements not defined here can be found in the + formal syntax of ABNF [RFC4234] and IMAP [RFC3501]. + + This document extends RFC 3501 [RFC3501] with two new search keys: + OLDER <interval> and YOUNGER <interval>. + + search-key =/ ( "OLDER" / "YOUNGER" ) SP nz-number + ; search-key defined in RFC 3501 + +4. Example + + C: a1 SEARCH UNSEEN YOUNGER 259200 + S: a1 * SEARCH 4 8 15 16 23 42 + + Search for all unseen messages within the past 3 days, or 259200 + seconds, according to the server's current time. + + + + +Burger Standards Track [Page 2] + +RFC 5032 Search Within September 2007 + + +5. Security Considerations + + The WITHIN extension does not raise any security considerations that + are not present in the base protocol. Considerations are the same as + for IMAP [RFC3501]. + +6. IANA Considerations + + Per the IMAP RFC [RFC3501], registration of a new IMAP capability in + the IMAP Capability registry requires the publication of a standards- + track RFC or an IESG approved experimental RFC. The registry is + currently located at + <http://www.iana.org/assignments/imap4-capabilities>. This + standards-track document defines the WITHIN IMAP capability. IANA + has added this extension to the IANA IMAP Capability registry. + +7. References + +7.1. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", RFC 2119, BCP 14, March 1997. + + [RFC3501] Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 3501, March 2003. + + [RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", RFC 4234, October 2005. + +7.2. Informative References + + [CONTEXT] Melnikov, D. and C. King, "Contexts for IMAP4", Work + in Progress, May 2006. + + + + + + + + + + + + + + + + + + +Burger Standards Track [Page 3] + +RFC 5032 Search Within September 2007 + + +Appendix A. Contributors + + Stephane Maes and Ray Cromwell wrote the original version of this + document as part of P-IMAP, as well as the first versions for the + IETF. From an attribution perspective, they are clearly authors. + +Appendix B. Acknowledgements + + The authors want to thank all who have contributed key insight and + who have extensively reviewed and discussed the concepts of LPSEARCH. + They also thank the authors of its early introduction in P-IMAP. + + We also want to give a special thanks to Arnt Gilbrandsen, Ken + Murchison, Zoltan Ordogh, and most especially Dave Cridland for their + review and suggestions. A special thank you goes to Alexey Melnikov + for his choice submission of text. + +Author's Address + + Eric W. Burger (editor) + BEA Systems, Inc. + USA + + EMail: eric.burger@bea.com + URI: http://www.standardstrack.com + + + + + + + + + + + + + + + + + + + + + + + + + + +Burger Standards Track [Page 4] + +RFC 5032 Search Within September 2007 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2007). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Burger Standards Track [Page 5] + diff --git a/imap/docs/rfc/rfc5051.txt b/imap/docs/rfc/rfc5051.txt new file mode 100644 index 00000000..0a4479ca --- /dev/null +++ b/imap/docs/rfc/rfc5051.txt @@ -0,0 +1,395 @@ + + + + + + +Network Working Group M. Crispin +Request for Comments: 5051 University of Washington +Category: Standards Track October 2007 + + + i;unicode-casemap - Simple Unicode Collation Algorithm + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + This document describes "i;unicode-casemap", a simple case- + insensitive collation for Unicode strings. It provides equality, + substring, and ordering operations. + +1. Introduction + + The "i;ascii-casemap" collation described in [COMPARATOR] is quite + simple to implement and provides case-independent comparisons for the + 26 Latin alphabetics. It is specified as the default and/or baseline + comparator in some application protocols, e.g., [IMAP-SORT]. + + However, the "i;ascii-casemap" collation does not produce + satisfactory results with non-ASCII characters. It is possible, with + a modest extension, to provide a more sophisticated collation with + greater multilingual applicability than "i;ascii-casemap". This + extension provides case-independent comparisons for a much greater + number of characters. It also collates characters with diacriticals + with the non-diacritical character forms. + + This collation, "i;unicode-casemap", is intended to be an alternative + to, and preferred over, "i;ascii-casemap". It does not replace the + "i;basic" collation described in [BASIC]. + +2. Unicode Casemap Collation Description + + The "i;unicode-casemap" collation is a simple collation which is + case-insensitive in its treatment of characters. It provides + equality, substring, and ordering operations. The validity test + operation returns "valid" for any input. + + + + + +Crispin Standards Track [Page 1] + +RFC 5051 i;unicode-casemap October 2007 + + + This collation allows strings in arbitrary (and mixed) character + sets, as long as the character set for each string is identified and + it is possible to convert the string to Unicode. Strings which have + an unidentified character set and/or cannot be converted to Unicode + are not rejected, but are treated as binary. + + Each input string is prepared by converting it to a "titlecased + canonicalized UTF-8" string according to the following steps, using + UnicodeData.txt ([UNICODE-DATA]): + + (1) A Unicode codepoint is obtained from the input string. + + (a) If the input string is in a known charset that can be + converted to Unicode, a sequence in the string's charset + is read and checked for validity according to the rules of + that charset. If the sequence is valid, it is converted + to a Unicode codepoint. Note that for input strings in + UTF-8, the UTF-8 sequence must be valid according to the + rules of [UTF-8]; e.g., overlong UTF-8 sequences are + invalid. + + (b) If the input string is in an unknown charset, or an + invalid sequence occurs in step (1)(a), conversion ceases. + No further preparation is performed, and any partial + preparation results are discarded. The original string is + used unchanged with the i;octet comparator. + + (2) The following steps, using UnicodeData.txt ([UNICODE-DATA]), + are performed on the resulting codepoint from step (1)(a). + + (a) If the codepoint has a titlecase property in + UnicodeData.txt (this is normally the same as the + uppercase property), the codepoint is converted to the + codepoints in the titlecase property. + + (b) If the resulting codepoint from (2)(a) has a decomposition + property of any type in UnicodeData.txt, the codepoint is + converted to the codepoints in the decomposition property. + This step is recursively applied to each of the resulting + codepoints until no more decomposition is possible + (effectively Normalization Form KD). + + Example: codepoint U+01C4 (LATIN CAPITAL LETTER DZ WITH CARON) + has a titlecase property of U+01C5 (LATIN CAPITAL LETTER D + WITH SMALL LETTER Z WITH CARON). Codepoint U+01C5 has a + decomposition property of U+0044 (LATIN CAPITAL LETTER D) + U+017E (LATIN SMALL LETTER Z WITH CARON). U+017E has a + decomposition property of U+007A (LATIN SMALL LETTER Z) U+030c + + + +Crispin Standards Track [Page 2] + +RFC 5051 i;unicode-casemap October 2007 + + + (COMBINING CARON). Neither U+0044, U+007A, nor U+030C have + any decomposition properties. Therefore, U+01C4 is converted + to U+0044 U+007A U+030C by this step. + + (3) The resulting codepoint(s) from step (2) is/are appended, in + UTF-8 format, to the "titlecased canonicalized UTF-8" string. + + (4) Repeat from step (1) until there is no more data in the input + string. + + Following the above preparation process on each string, the equality, + ordering, and substring operations are as for i;octet. + + It is permitted to use an alternative implementation of the above + preparation process if it produces the same results. For example, it + may be more convenient for an implementation to convert all input + strings to a sequence of UTF-16 or UTF-32 values prior to performing + any of the step (2) actions. Similarly, if all input strings are (or + are convertible to) Unicode, it may be possible to use UTF-32 as an + alternative to UTF-8 in step (3). + + Note: UTF-16 is unsuitable as an alternative to UTF-8 in step (3), + because UTF-16 surrogates will cause i;octet to collate codepoints + U+E0000 through U+FFFF after non-BMP codepoints. + + This collation is not locale sensitive. Consequently, care should be + taken when using OS-supplied functions to implement this collation. + Functions such as strcasecmp and toupper are sometimes locale + sensitive and may inconsistently casemap letters. + + The i;unicode-casemap collation is well suited to use with many + Internet protocols and computer languages. Use with natural language + is often inappropriate; even though the collation apparently supports + languages such as Swahili and English, in real-world use it tends to + mis-sort a number of types of string: + + o people and place names containing scripts that are not collated + according to "alphabetical order". + o words with characters that have diacriticals. However, + i;unicode-casemap generally does a better job than i;ascii-casemap + for most (but not all) languages. For example, German umlaut + letters will sort correctly, but some Scandinavian letters will + not. + o names such as "Lloyd" (which in Welsh sorts after "Lyon", unlike + in English), + o strings containing other non-letter symbols; e.g., euro and pound + sterling symbols, quotation marks other than '"', dashes/hyphens, + etc. + + + +Crispin Standards Track [Page 3] + +RFC 5051 i;unicode-casemap October 2007 + + +3. Unicode Casemap Collation Registration + + <?xml version='1.0'?> + <!DOCTYPE collation SYSTEM 'collationreg.dtd'> + <collation rfc="5051" scope="global" intendedUse="common"> + <identifier>i;unicode-casemap</identifier> + <title>Unicode Casemap</title> + <operations>equality order substring</operations> + <specification>RFC 5051</specification> + <owner>IETF</owner> + <submitter>mrc@cac.washington.edu</submitter> + </collation> + +4. Security Considerations + + The security considerations for [UTF-8], [STRINGPREP], and [UNICODE- + SECURITY] apply and are normative to this specification. + + The results from this comparator will vary depending upon the + implementation for several reasons. Implementations MUST consider + whether these possibilities are a problem for their use case: + + 1) New characters added in Unicode may have decomposition or + titlecase properties that will not be known to an implementation + based upon an older revision of Unicode. This impacts step (2). + + 2) Step (2)(b) defines a subset of Normalization Form KD (NFKD) that + does not require normalization of out-of-order diacriticals. + However, an implementation MAY use an NFKD library routine that + does such normalization. This impacts step (2)(b) and possibly + also step (1)(a), and is an issue only with ill-formed UTF-8 + input. + + 3) The set of charsets handled in step (1)(a) is open-ended. UTF-8 + (and, by extension, US-ASCII) are the only mandatory-to-implement + charsets. This impacts step (1)(a). + + Implementations SHOULD, as far as feasible, support all the + charsets they are likely to encounter in the input data, in order + to avoid poor collation caused by the fall through to the (1)(b) + rule. + + 4) Other charsets may have revisions which add new characters that + are not known to an implementation based upon an older revision. + This impacts step (1)(a) and possibly also step (1)(b). + + + + + + +Crispin Standards Track [Page 4] + +RFC 5051 i;unicode-casemap October 2007 + + + An attacker may create input that is ill-formed or in an unknown + charset, with the intention of impacting the results of this + comparator or exploiting other parts of the system which process this + input in different ways. Note, however, that even well-formed data + in a known charset can impact the result of this comparator in + unexpected ways. For example, an attacker can substitute U+0041 + (LATIN CAPITAL LETTER A) with U+0391 (GREEK CAPITAL LETTER ALPHA) or + U+0410 (CYRILLIC CAPITAL LETTER A) in the intention of causing a + non-match of strings which visually appear the same and/or causing + the string to appear elsewhere in a sort. + +5. IANA Considerations + + The i;unicode-casemap collation defined in section 2 has been added + to the registry of collations defined in [COMPARATOR]. + +6. Normative References + + [COMPARATOR] Newman, C., Duerst, M., and A. Gulbrandsen, + "Internet Application Protocol Collation + Registry", RFC 4790, February 2007. + + [STRINGPREP] Hoffman, P. and M. Blanchet, "Preparation of + Internationalized Strings ("stringprep")", RFC + 3454, December 2002. + + [UTF-8] Yergeau, F., "UTF-8, a transformation format of + ISO 10646", STD 63, RFC 3629, November 2003. + + [UNICODE-DATA] <http://www.unicode.org/Public/UNIDATA/ + UnicodeData.txt> + + Although the UnicodeData.txt file referenced + here is part of the Unicode standard, it is + subject to change as new characters are added + to Unicode and errors are corrected in Unicode + revisions. As a result, it may be less stable + than might otherwise be implied by the + standards status of this specification. + + [UNICODE-SECURITY] Davis, M. and M. Suignard, "Unicode Security + Considerations", February 2006, + <http://www.unicode.org/reports/tr36/>. + + + + + + + + +Crispin Standards Track [Page 5] + +RFC 5051 i;unicode-casemap October 2007 + + +7. Informative References + + [BASIC] Newman, C., Duerst, M., and A. Gulbrandsen, + "i;basic - the Unicode Collation Algorithm", + Work in Progress, March 2007. + + [IMAP-SORT] Crispin, M. and K. Murchison, "Internet Message + Access Protocol - SORT and THREAD Extensions", + Work in Progress, September 2007. + +Author's Address + + Mark R. Crispin + Networks and Distributed Computing + University of Washington + 4545 15th Avenue NE + Seattle, WA 98105-4527 + + Phone: +1 (206) 543-5762 + EMail: MRC@CAC.Washington.EDU + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Crispin Standards Track [Page 6] + +RFC 5051 i;unicode-casemap October 2007 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2007). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Crispin Standards Track [Page 7] + diff --git a/imap/docs/rfc/rfc5092.txt b/imap/docs/rfc/rfc5092.txt new file mode 100644 index 00000000..ab87f350 --- /dev/null +++ b/imap/docs/rfc/rfc5092.txt @@ -0,0 +1,1795 @@ + + + + + + +Network Working Group A. Melnikov, Ed. +Request for Comments: 5092 Isode Ltd. +Obsoletes: 2192 C. Newman +Updates: 4467 Sun Microsystems +Category: Standards Track November 2007 + + + IMAP URL Scheme + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + IMAP (RFC 3501) is a rich protocol for accessing remote message + stores. It provides an ideal mechanism for accessing public mailing + list archives as well as private and shared message stores. This + document defines a URL scheme for referencing objects on an IMAP + server. + + This document obsoletes RFC 2192. It also updates RFC 4467. + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov & Newman Standards Track [Page 1] + +RFC 5092 IMAP URL Scheme November 2007 + + +Table of Contents + + 1. Introduction ....................................................2 + 2. Conventions Used in This Document ...............................3 + 3. IMAP userinfo Component (iuserinfo) .............................4 + 3.1. IMAP Mailbox Naming Scope ..................................4 + 3.2. IMAP User Name and Authentication Mechanism ................4 + 3.3. Limitations of enc-user ....................................6 + 4. IMAP Server .....................................................7 + 5. Lists of Messages ...............................................7 + 6. A Specific Message or Message Part ..............................8 + 6.1. URLAUTH Authorized URL .....................................9 + 6.1.1. Concepts ............................................9 + 6.1.1.1. URLAUTH ....................................9 + 6.1.1.2. Mailbox Access Key .........................9 + 6.1.1.3. Authorized Access Identifier ...............9 + 6.1.1.4. Authorization Mechanism ...................10 + 6.1.1.5. Authorization Token .......................10 + 6.1.2. URLAUTH Extensions to IMAP URL .....................10 + 7. Relative IMAP URLs .............................................11 + 7.1. absolute-path References ..................................12 + 7.2. relative-path References ..................................12 + 8. Internationalization Considerations ............................13 + 9. Examples .......................................................13 + 9.1. Examples of Relative URLs .................................16 + 10. Security Considerations .......................................16 + 10.1. Security Considerations Specific to URLAUTH Authorized + URL ......................................................17 + 11. ABNF for IMAP URL Scheme ......................................17 + 12. IANA Considerations ...........................................21 + 12.1. IANA Registration of imap: URI Scheme ....................21 + 13. References ....................................................22 + 13.1. Normative References .....................................22 + 13.2. Informative References ...................................23 + Appendix A. Sample Code............................................24 + Appendix B. List of Changes since RFC 2192.........................30 + Appendix C. List of Changes since RFC 4467.........................31 + Appendix D. Acknowledgments........................................31 + +1. Introduction + + The IMAP URL scheme is used to designate IMAP servers, mailboxes, + messages, MIME bodies [MIME], and search programs on Internet hosts + accessible using the IMAP protocol over TCP. + + The IMAP URL follows the common Internet scheme syntax as defined in + [URI-GEN]. If :<port> is omitted, the port defaults to 143 (as + defined in Section 2.1 of [IMAP4]). + + + +Melnikov & Newman Standards Track [Page 2] + +RFC 5092 IMAP URL Scheme November 2007 + + + An absolute IMAP URL takes one of the following forms: + + imap://<iserver>[/] + + imap://<iserver>/<enc-mailbox>[<uidvalidity>][?<enc-search>] + + imap://<iserver>/<enc-mailbox>[<uidvalidity>]<iuid> + [<isection>][<ipartial>][<iurlauth>] + + The first form is used to refer to an IMAP server (see Section 4), + the second form refers to the contents of a mailbox or a set of + messages resulting from a search (see Section 5), and the final form + refers to a specific message or message part, and possibly a byte + range in that part (see Section 6). If [URLAUTH] extension is + supported, then the final form can have the <iurlauth> component (see + Section 6.1 for more details). + + The <iserver> component common to all types of absolute IMAP URLs has + the following syntax expressed in ABNF [ABNF]: + + [iuserinfo "@"] host [ ":" port ] + + The <iserver> component is the same as "authority" defined in + [URI-GEN]. The syntax and uses of the <iuserinfo> ("IMAP userinfo + component") are described in detail in Section 3. The syntax of + <host> and <port> is described in [URI-GEN]. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [KEYWORDS]. + + This document references many productions from [URI-GEN]. When the + document needs to emphasize IMAP URI-specific differences from [URI- + GEN] (i.e., for parts of IMAP URIs that have more restricted syntax + than generic URIs), it uses a non-terminal i<foo> to define an IMAP- + specific version of the non-terminal <foo> from [URI-GEN]. + + Note that the ABNF syntax shown in Section 11 is normative. Sections + 2-6 may use a less formal syntax that does not necessarily match the + normative ABNF shown in Section 11. If there are any differences + between the syntax shown in Sections 2-6 and Section 11, then the + syntax shown in Section 11 must be treated as authoritative. Non- + syntax requirements included in Sections 2-6 are, of course, + normative. + + + + + +Melnikov & Newman Standards Track [Page 3] + +RFC 5092 IMAP URL Scheme November 2007 + + +3. IMAP userinfo Component (iuserinfo) + + The <iuserinfo> component conforms to the generic syntax of + <userinfo> defined in [URI-GEN]. It has the following syntax + expressed in ABNF [ABNF]: + + enc-user [iauth] / [enc-user] iauth + + The meaning of the different parts is described in subsections of + this section. + +3.1. IMAP Mailbox Naming Scope + + The "enc-user" part of the "iuserinfo" component, if present, denotes + mailbox naming scope. If it is absent, the IMAP URL can only + reference mailboxes with globally unique names, i.e., mailboxes with + names that don't change depending on the user the client + authenticated as to the IMAP server. Note that not all IMAP + implementations support globally unique names. + + For example, a personal mailbox described by the following URL + <imap://michael@example.org/INBOX> is most likely different from a + personal mailbox described by <imap://bester@example.org/INBOX>, even + though both URLs use the same mailbox name. + +3.2. IMAP User Name and Authentication Mechanism + + The userinfo component (see [URI-GEN]) of an IMAP URI may contain an + IMAP user name (a.k.a. authorization identity [SASL], "enc-user") + and/or an authentication mechanism. (Note that the "enc-user" also + defines a mailbox naming scope as described in Section 3.1). The + IMAP user name and the authentication mechanism are used in the + "LOGIN" or "AUTHENTICATE" commands after making the connection to the + IMAP server. + + If no user name and no authentication mechanism are supplied, the + client MUST authenticate as anonymous to the server. If the server + advertises AUTH=ANONYMOUS IMAP capability, the client MUST use the + AUTHENTICATE command with ANONYMOUS [ANONYMOUS] SASL mechanism. If + SASL ANONYMOUS is not available, the (case-insensitive) user name + "anonymous" is used with the "LOGIN" command and the Internet email + address of the end user accessing the resource is supplied as the + password. The latter option is given in order to provide for + interoperability with deployed servers. + + Note that, as described in RFC 3501, the "LOGIN" command MUST NOT be + used when the IMAP server advertises the LOGINDISABLED capability. + + + + +Melnikov & Newman Standards Track [Page 4] + +RFC 5092 IMAP URL Scheme November 2007 + + + An authentication mechanism (as used by the IMAP AUTHENTICATE + command) can be expressed by adding ";AUTH=<enc-auth-type>" to the + end of the user name in an IMAP URL. When such an <enc-auth-type> is + indicated, the client SHOULD request appropriate credentials from + that mechanism and use the "AUTHENTICATE" command instead of the + "LOGIN" command. If no user name is specified, one MUST be obtained + from the mechanism or requested from the user/configuration as + appropriate. + + The string ";AUTH=*" indicates that the client SHOULD select an + appropriate authentication mechanism. (Though the '*' character in + this usage is not strictly a delimiter, it is being treated like a + sub-delim [URI-GEN] in this instance. It MUST NOT be percent-encoded + in this usage, as ";AUTH=%2A" will not match this production.) It + MAY use any mechanism listed in the response to the CAPABILITY + command (or CAPABILITY response code) or use an out-of-band security + service resulting in a PREAUTH connection. If no user name is + specified and no appropriate authentication mechanisms are available, + the client SHOULD fall back to anonymous login as described above. + The behavior prescribed in this section allows a URL that grants + read-write access to authorized users and read-only anonymous access + to other users. + + If a user name is included with no authentication mechanism, then + ";AUTH=*" is assumed. + + Clients must take care when resolving a URL that requires or requests + any sort of authentication, since URLs can easily come from untrusted + sources. Supplying authentication credentials to the wrong server + may compromise the security of the user's account; therefore, the + program resolving the URL should meet at least one of the following + criteria in this case: + + 1) The URL comes from a trusted source, such as a referral server + that the client has validated and trusts according to site policy. + Note that user entry of the URL may or may not count as a trusted + source, depending on the experience level of the user and site + policy. + + 2) Explicit local site policy permits the client to connect to the + server in the URL. For example, a company example.com may have a + site policy to trust all IMAP server names ending in example.com, + whereas such a policy would be unwise for example.edu where random + students can set up IMAP servers. + + 3) The user confirms that connecting to that domain name with the + specified credentials and/or mechanism is permitted. For example, + when using "LOGIN" or SASL PLAIN with Transport Layer Security + + + +Melnikov & Newman Standards Track [Page 5] + +RFC 5092 IMAP URL Scheme November 2007 + + + (TLS), the IMAP URL client presents a dialog box "Is it OK to send + your password to server "example.com"? Please be aware the owners + of example.com will be able to reuse your password to connect to + other servers on your behalf". + + 4) A mechanism is used that validates the server before passing + potentially compromising client credentials. For example, a site + has a designated TLS certificate used to certify site-trusted IMAP + server certificates, and this has been configured explicitly into + the IMAP URL client. Another example is use of a Simple + Authentication and Security Layer (SASL) mechanism such as + DIGEST-MD5 [DIGEST-MD5], which supports mutual authentication. + + 5) An authentication mechanism is used that will not reveal any + information to the server that could be used to compromise future + connections. Examples are SASL ANONYMOUS [ANONYMOUS] or GSSAPI + [GSSAPI]. + + URLs that do not include a user name but include an authentication + mechanism (";AUTH=<mech>") must be treated with extra care, since for + some <mech>s they are more likely to compromise the user's primary + account. A URL containing ";AUTH=*" must also be treated with extra + care since it might fall back on a weaker security mechanism. + Finally, clients are discouraged from using a plaintext password as a + fallback with ";AUTH=*" unless the connection has strong encryption. + + A program interpreting IMAP URLs MAY cache open connections to an + IMAP server for later reuse. If a URL contains a user name, only + connections authenticated as that user may be reused. If a URL does + not contain a user name or authentication mechanism, then only an + anonymous connection may be reused. + + Note that if unsafe or reserved characters such as " " (space) or ";" + are present in the user name or authentication mechanism, they MUST + be percent-encoded as described in [URI-GEN]. + +3.3. Limitations of enc-user + + As per Sections 3.1 and 3.2 of this document, the IMAP URI enc-user + has two purposes: + + 1) It provides context for user-specific mailbox paths such as + "INBOX" (Section 3.1). + + 2) It specifies that resolution of the URL requires logging in as + that user and limits use of that URL to only that user (Section + 3.2). + + + + +Melnikov & Newman Standards Track [Page 6] + +RFC 5092 IMAP URL Scheme November 2007 + + + An obvious limitation of using the same field for both purposes is + that the URL can be resolved only by the mailbox owner. In order to + avoid this restriction, implementations should use globally unique + mailbox names (see Section 3.1) whenever possible. + + Note: There is currently no general way in IMAP of learning a + globally unique name for a mailbox. However, by looking at the + NAMESPACE [NAMESPACE] command result, it is possible to determine + whether or not a mailbox name is globally unique. + + The URLAUTH component overrides the second purpose of the enc-user in + the IMAP URI and by default permits the URI to be resolved by any + user permitted by the <access> identifier. URLAUTH and <access> + identifier are described in Section 6.1. + +4. IMAP Server + + An IMAP URL referring to an IMAP server has the following form: + + imap://<iserver>[/] + + This URL type is frequently used to describe a location of an IMAP + server, both in referrals and in configuration. It may optionally + contain the <iuserinfo> component (see Sections 3 and 11). A program + interpreting this URL would issue the standard set of commands it + uses to present a view of the content of the IMAP server, as visible + to the user described by the "enc-user" part of the <iuserinfo> + component, if the "enc-user" part is specified. + +5. Lists of Messages + + An IMAP URL referring to a list of messages has the following form: + + imap://<iserver>/<enc-mailbox>[<uidvalidity>][?<enc-search>] + + The <enc-mailbox> field is used as the argument to the IMAP4 "SELECT" + or "EXAMINE" command. Note that if unsafe or reserved characters + such as " " (space), ";", or "?" are present in <enc-mailbox>, they + MUST be percent-encoded as described in [URI-GEN]. + + The <uidvalidity> field is optional. If it is present, it MUST be + the same as the value of IMAP4 UIDVALIDITY response code at the time + the URL was created. This MUST be used by the program interpreting + the IMAP URL to determine if the URL is stale. If the IMAP URL is + stale, then the program should behave as if the corresponding mailbox + doesn't exist. + + + + + +Melnikov & Newman Standards Track [Page 7] + +RFC 5092 IMAP URL Scheme November 2007 + + + Note that the <uidvalidity> field is a modifier to the <enc-mailbox>, + i.e., it is considered a part of the last "component" (as used in + [URI-GEN]) of the <enc-mailbox>. This is significant during relative + URI resolution. + + The "?<enc-search>" field is optional. If it is not present, the + program interpreting the URL will present the entire content of the + mailbox. + + If the "?<enc-search>" field is present, the program interpreting the + URL should use the contents of this field as arguments following an + IMAP4 SEARCH command. These arguments are likely to contain unsafe + characters such as " " (space) (which are likely to be present in the + <enc-search>). If unsafe characters are present, they MUST be + percent-encoded as described in [URI-GEN]. + + Note that quoted strings and non-synchronizing literals [LITERAL+] + are allowed in the <enc-search> content; however, synchronizing + literals are not allowed, as their presence would effectively mean + that the agent interpreting IMAP URLs needs to parse an <enc-search> + content, find all synchronizing literals, and perform proper command + continuation request handling (see Sections 4.3 and 7 of [IMAP4]). + +6. A Specific Message or Message Part + + An IMAP URL referring to a specific message or message part has the + following form: + + imap://<iserver>/<enc-mailbox>[<uidvalidity>]<iuid> + [<isection>][<ipartial>][<iurlauth>] + + The <enc-mailbox> and [uidvalidity] are as defined in Section 5 + above. + + If <uidvalidity> is present in this form, it SHOULD be used by the + program interpreting the URL to determine if the URL is stale. + + The <iuid> refers to an IMAP4 message Unique Identifier (UID), and it + SHOULD be used as the <set> argument to the IMAP4 "UID FETCH" + command. + + The <isection> field is optional. If not present, the URL refers to + the entire Internet message as returned by the IMAP command "UID + FETCH <uid> BODY.PEEK[]". If present, the URL refers to the object + returned by a "UID FETCH <uid> BODY.PEEK[<section>]" command. The + type of the object may be determined by using a "UID FETCH <uid> + BODYSTRUCTURE" command and locating the appropriate part in the + + + + +Melnikov & Newman Standards Track [Page 8] + +RFC 5092 IMAP URL Scheme November 2007 + + + resulting BODYSTRUCTURE. Note that unsafe characters in [isection] + MUST be percent-encoded as described in [URI-GEN]. + + The <ipartial> field is optional. If present, it effectively appends + "<<partial-range>>" to the end of the UID FETCH BODY.PEEK[<section>] + command constructed as described in the previous paragraph. In other + words, it allows the client to request a byte range of the + message/message part. + + The <iurlauth> field is described in detail in Section 6.1. + +6.1. URLAUTH Authorized URL + + URLAUTH authorized URLs are only supported by an IMAP server + advertising the URLAUTH IMAP capability [URLAUTH]. + +6.1.1. Concepts + +6.1.1.1. URLAUTH + + URLAUTH is a component, appended at the end of a URL, that conveys + authorization to access the data addressed by that URL. It contains + an authorized access identifier, an authorization mechanism name, and + an authorization token. The authorization token is generated from + the URL, the authorized access identifier, authorization mechanism + name, and a mailbox access key. + + Note: This specification only allows for the URLAUTH component in + IMAP URLs describing a message or its part. + +6.1.1.2. Mailbox Access Key + + The mailbox access key is an unpredictable, random string. To ensure + unpredictability, the random string with at least 128 bits of entropy + is generated by software or hardware (not by the human user). + + Each user has a table of mailboxes and an associated mailbox access + key for each mailbox. Consequently, the mailbox access key is per- + user and per-mailbox. In other words, two users sharing the same + mailbox each have a different mailbox access key for that mailbox, + and each mailbox accessed by a single user also has a different + mailbox access key. + +6.1.1.3. Authorized Access Identifier + + The authorized <access> identifier restricts use of the URLAUTH + authorized URL to certain users authorized on the server, as + described in Section 6.1.2. + + + +Melnikov & Newman Standards Track [Page 9] + +RFC 5092 IMAP URL Scheme November 2007 + + +6.1.1.4. Authorization Mechanism + + The authorization mechanism is the algorithm by which the URLAUTH is + generated and subsequently verified, using the mailbox access key. + +6.1.1.5. Authorization Token + + The authorization token is a deterministic string of at least 128 + bits that an entity with knowledge of the secret mailbox access key + and URL authorization mechanism can use to verify the URL. + +6.1.2. URLAUTH Extensions to IMAP URL + + A specific message or message part IMAP URL can optionally contain + ";EXPIRE=<datetime>" and/or ";URLAUTH=<access>:<mech>:<token>". + + When ";EXPIRE=<datetime>" is used, this indicates the latest date and + time that the URL is valid. After that date and time, the URL has + expired and server implementations MUST reject the URL. If + ";EXPIRE=<datetime>" is not used, the URL has no expiration, but can + still be revoked using the RESETKEY command [URLAUTH]. + + The URLAUTH takes the form ";URLAUTH=<access>:<mech>:<token>", and it + MUST be at the end of the URL. It is composed of three parts. The + <access> portion provides the authorized access identifiers that may + constrain the operations and users that are permitted to use this + URL. The <mech> portion provides the authorization mechanism used by + the IMAP server to generate the authorization token that follows. + The <token> portion provides the authorization token, which can be + generated using the GENURLAUTH command [URLAUTH]. + + The "submit+" <access> identifier prefix, followed by a userid, + indicates that only a userid authorized as a message submission + entity on behalf of the specified userid is permitted to use this + URL. The IMAP server does not validate the specified userid but does + validate that the IMAP session has an authorization identity that is + authorized as a message submission entity. The authorized message + submission entity MUST validate the userid prior to contacting the + IMAP server. + + The "user+" <access> identifier prefix, followed by a userid, + indicates that use of this URL is limited to IMAP sessions that are + logged in as the specified userid (that is, have authorization + identity as that userid). + + Note: If a SASL mechanism that provides both authorization and + authentication identifiers is used to authenticate to the IMAP + server, the "user+" <access> identifier MUST match the + + + +Melnikov & Newman Standards Track [Page 10] + +RFC 5092 IMAP URL Scheme November 2007 + + + authorization identifier. If the SASL mechanism can't transport + the authorization identifier, the "user+" <access> identifier MUST + match the authorization identifier derived from the authentication + identifier (see [SASL]). + + The "authuser" <access> identifier indicates that use of this URL is + limited to authenticated IMAP sessions that are logged in as any + non-anonymous user (that is, have authorization identity as a non- + anonymous user) of that IMAP server. To restate this: use of this + type of URL is prohibited to anonymous IMAP sessions, i.e., any + URLFETCH command containing this type of URL issued in an anonymous + session MUST return NIL in the URLFETCH response. + + The "anonymous" <access> identifier indicates that use of this URL is + not restricted by session authorization identity; that is, any IMAP + session in authenticated or selected state (as defined in [IMAP4]), + including anonymous sessions, may issue a URLFETCH [URLAUTH] using + this URL. + + The authorization token is represented as an ASCII-encoded + hexadecimal string, which is used to authorize the URL. The length + and the calculation of the authorization token depend upon the + mechanism used, but in all cases, the authorization token is at least + 128 bits (and therefore at least 32 hexadecimal digits). + + Example: + + <imap://joe@example.com/INBOX/;uid=20/;section=1.2;urlauth= + submit+fred:internal:91354a473744909de610943775f92038> + +7. Relative IMAP URLs + + Relative IMAP URLs are permitted and are resolved according to the + rules defined in [URI-GEN]. In particular, in IMAP URLs parameters + (such as ";uid=" or ";section=") are treated as part of the normal + path with respect to relative URL resolution. + + [URI-GEN] defines four forms of relative URLs: <inetwork-path>, + <iabsolute-path>, <irelative-path>, and <ipath-empty>. Their syntax + is defined in Section 11. + + A relative reference that begins with two slash characters is termed + a network-path reference (<inetwork-path>); such references are + rarely used, because in most cases they can be replaced with an + equivalent absolute URL. A relative reference that begins with a + single slash character is termed an absolute-path reference + (<iabsolute-path>; see also Section 7.1). A relative reference that + does not begin with a slash character is termed a relative-path + + + +Melnikov & Newman Standards Track [Page 11] + +RFC 5092 IMAP URL Scheme November 2007 + + + reference (<irelative-path>; see also Section 7.2). The final form + is <ipath-empty>, which is "same-document reference" (see Section 4.4 + of [URI-GEN]). + + The following observations about relative URLs are important: + + The <iauth> grammar element (which is a part of <iuserinfo>, which + is, in turn, a part of <iserver>; see Section 3) is considered part + of the user name for purposes of resolving relative IMAP URLs. This + means that unless a new user name/server specification is included in + the relative URL, the authentication mechanism is inherited from the + base IMAP URL. + + URLs always use "/" as the hierarchy delimiter for the purpose of + resolving paths in relative URLs. IMAP4 permits the use of any + hierarchy delimiter in mailbox names. For this reason, relative + mailbox paths will only work if the mailbox uses "/" as the hierarchy + delimiter. Relative URLs may be used on mailboxes that use other + delimiters, but in that case, the entire mailbox name MUST be + specified in the relative URL or inherited as a whole from the base + URL. + + If an IMAP server allows for mailbox names starting with "./" or + "../", ending with "/." or "/..", or containing sequences "/../" or + "/./", then such mailbox names MUST be percent-encoded as described + in [URI-GEN]. Otherwise, they would be misinterpreted as dot- + segments (see Section 3.3 of [URI-GEN]), which are processed + specially during the relative path resolution process. + +7.1. absolute-path References + + A relative reference that begins with a single slash character is + termed an absolute-path reference (see Section 4.2 of [URI-GEN]). If + an IMAP server permits mailbox names with a leading "/", then the + leading "/" MUST be percent-encoded as described in [URI-GEN]. + Otherwise, the produced absolute-path reference URI will be + misinterpreted as a network-path reference [URI-GEN] described by the + <inetwork-path> non-terminal. + +7.2. relative-path References + + A relative reference that does not begin with a slash character is + termed a relative-path reference [URI-GEN]. Implementations MUST NOT + generate or accept relative-path IMAP references. + + See also Section 4.2 of [URI-GEN] for restrictions on relative-path + references. + + + + +Melnikov & Newman Standards Track [Page 12] + +RFC 5092 IMAP URL Scheme November 2007 + + +8. Internationalization Considerations + + IMAP4, Section 5.1.3 [IMAP4] includes a convention for encoding non- + US-ASCII characters in IMAP mailbox names. Because this convention + is private to IMAP, it is necessary to convert IMAP's encoding to one + that can be more easily interpreted by a URL display program. For + this reason, IMAP's modified UTF-7 encoding for mailboxes MUST be + converted to UTF-8 [UTF-8]. Since 8-bit octets are not permitted in + URLs, the UTF-8 octets are percent-encoded as required by the URL + specification [URI-GEN], Section 2.1. Sample code is included in + Appendix A to demonstrate this conversion. + + IMAP user names are UTF-8 strings and MUST be percent-encoded as + required by the URL specification [URI-GEN], Section 2.1. + + Also note that IMAP SEARCH criteria can contain non-US-ASCII + characters. 8-bit octets in those strings MUST be percent-encoded as + required by the URL specification [URI-GEN], Section 2.1. + +9. Examples + + The following examples demonstrate how an IMAP4 client program might + translate various IMAP4 URLs into a series of IMAP4 commands. + Commands sent from the client to the server are prefixed with "C:", + and responses sent from the server to the client are prefixed with + "S:". + + The URL: + + <imap://minbari.example.org/gray-council;UIDVALIDITY=385759045/; + UID=20/;PARTIAL=0.1024> + + may result in the following client commands and server responses: + + <connect to minbari.example.org, port 143> + S: * OK [CAPABILITY IMAP4rev1 STARTTLS AUTH=ANONYMOUS] Welcome + C: A001 AUTHENTICATE ANONYMOUS + S: + + C: c2hlcmlkYW5AYmFieWxvbjUuZXhhbXBsZS5vcmc= + S: A001 OK Welcome sheridan@babylon5.example.org + C: A002 SELECT gray-council + <client verifies the UIDVALIDITY matches> + C: A003 UID FETCH 20 BODY.PEEK[]<0.1024> + + The URL: + + <imap://psicorp.example.org/~peter/%E6%97%A5%E6%9C%AC%E8%AA%9E/ + %E5%8F%B0%E5%8C%97> + + + +Melnikov & Newman Standards Track [Page 13] + +RFC 5092 IMAP URL Scheme November 2007 + + + may result in the following client commands: + + <connect to psicorp.example.org, port 143> + S: * OK [CAPABILITY IMAP4rev1 STARTTLS AUTH=CRAM-MD5] Welcome + C: A001 LOGIN ANONYMOUS bester@psycop.psicorp.example.org + C: A002 SELECT ~peter/&ZeVnLIqe-/&U,BTFw- + <commands the client uses for viewing the contents of + the mailbox> + + The URL: + + <imap://;AUTH=GSSAPI@minbari.example.org/gray-council/;uid=20/ + ;section=1.2> + + may result in the following client commands: + + <connect to minbari.example.org, port 143> + S: * OK Greetings + C: A000 CAPABILITY + S: * CAPABILITY IMAP4rev1 STARTTLS AUTH=GSSAPI + S: A000 OK + C: A001 AUTHENTICATE GSSAPI + <authentication exchange> + C: A002 SELECT gray-council + C: A003 UID FETCH 20 BODY.PEEK[1.2] + + If the following relative URL is located in that body part: + + <;section=1.4> + + this could result in the following client commands: + + C: A004 UID FETCH 20 (BODY.PEEK[1.2.MIME] + BODY.PEEK[1.MIME] + BODY.PEEK[HEADER.FIELDS (Content-Location)]) + <Client looks for Content-Location headers in + result. If no such headers, then it does the following> + C: A005 UID FETCH 20 BODY.PEEK[1.4] + + The URL: + + <imap://;AUTH=*@minbari.example.org/gray%20council? + SUBJECT%20shadows> + + + + + + + + +Melnikov & Newman Standards Track [Page 14] + +RFC 5092 IMAP URL Scheme November 2007 + + + could result in the following: + + <connect to minbari.example.org, port 143> + S: * OK Welcome + C: A001 CAPABILITY + S: * CAPABILITY IMAP4rev1 AUTH=DIGEST-MD5 + S: A001 OK + C: A002 AUTHENTICATE DIGEST-MD5 + <authentication exchange> + S: A002 OK user lennier authenticated + C: A003 SELECT "gray council" + ... + C: A004 SEARCH SUBJECT shadows + S: * SEARCH 8 10 13 14 15 16 + S: A004 OK SEARCH completed + C: A005 FETCH 8,10,13:16 ALL + ... + + In the example above, the client has implementation-dependent + choices. The authentication mechanism could be anything, including + PREAUTH. The final FETCH command could fetch more or less + information about the messages, depending on what it wishes to + display to the user. + + The URL: + + <imap://john;AUTH=*@minbari.example.org/babylon5/personel? + charset%20UTF-8%20SUBJECT%20%7B14+%7D%0D%0A%D0%98%D0%B2% + D0%B0%D0%BD%D0%BE%D0%B2%D0%B0> + + shows that 8-bit data can be sent using non-synchronizing literals + [LITERAL+]. This could result in the following: + + <connect to minbari.example.org, port 143> + S: * OK Hi there + C: A001 CAPABILITY + S: * CAPABILITY IMAP4rev1 LITERAL+ AUTH=DIGEST-MD5 + S: A001 OK + C: A002 AUTHENTICATE DIGEST-MD5 + <authentication exchange> + S: A002 OK user john authenticated + C: A003 SELECT babylon5/personel + ... + C: A004 SEARCH CHARSET UTF-8 SUBJECT {14+} + C: XXXXXXXXXXXXXX + S: * SEARCH 7 10 12 + S: A004 OK SEARCH completed + C: A005 FETCH 7,10,12 ALL + + + +Melnikov & Newman Standards Track [Page 15] + +RFC 5092 IMAP URL Scheme November 2007 + + + ... + + where XXXXXXXXXXXXXX is 14 bytes of UTF-8 encoded data as specified + in the URL above. + +9.1. Examples of Relative URLs + + The following absolute-path reference + + </foo/;UID=20/..> + + is the same as + + </foo> + + That is, both of them reference the mailbox "foo" located on the IMAP + server described by the corresponding Base URI. + + The following relative-path reference + + <;UID=20> + + references a message with UID in the mailbox specified by the Base + URI. + + The following edge case example demonstrates that the ;UIDVALIDITY= + modifier is a part of the mailbox name as far as relative URI + resolution is concerned: + + <..;UIDVALIDITY=385759045/;UID=20> + + In this example, ".." is not a dot-segment [URI-GEN]. + +10. Security Considerations + + Security considerations discussed in the IMAP specification [IMAP4] + and the URI specification [URI-GEN] are relevant. Security + considerations related to authenticated URLs are discussed in Section + 3.2 of this document. + + Many email clients store the plaintext password for later use after + logging into an IMAP server. Such clients MUST NOT use a stored + password in response to an IMAP URL without explicit permission from + the user to supply that password to the specified host name. + + Clients resolving IMAP URLs that wish to achieve data confidentiality + and/or integrity SHOULD use the STARTTLS command (if supported by the + + + + +Melnikov & Newman Standards Track [Page 16] + +RFC 5092 IMAP URL Scheme November 2007 + + + server) before starting authentication, or use a SASL mechanism, such + as GSSAPI, that provides a confidentiality security layer. + +10.1. Security Consideration Specific to URLAUTH Authorized URL + + The "user+<userid>" <access> identifier limits resolution of that URL + to a particular userid, whereas the "submit+<userid>" <access> + identifier is more general and simply requires that the session be + authorized by a user that has been granted a "submit" role within the + authentication system. Use of either of these mechanisms limits the + scope of the URL. An attacker who cannot authenticate using the + appropriate credentials cannot make use of the URL. + + The "authuser" and "anonymous" <access> identifiers do not have this + level of protection. These access identifiers are primarily useful + for public export of data from an IMAP server, without requiring that + it be copied to a web or anonymous FTP server. + + The decision to use the "authuser" <access> identifier should be made + with caution. An "authuser" <access> identifier can be used by any + authorized user of the IMAP server; therefore, use of this access + identifier should be limited to content that may be disclosed to any + authorized user of the IMAP server. + + The decision to use the "anonymous" <access> identifier should be + made with extreme caution. An "anonymous" <access> identifier can be + used by anyone; therefore, use of this access identifier should be + limited to content that may be disclosed to anyone. + +11. ABNF for IMAP URL Scheme + + Formal syntax is defined using ABNF [ABNF], extending the ABNF rules + in Section 9 of [IMAP4]. Elements not defined here can be found in + [ABNF], [IMAP4], [IMAPABNF], or [URI-GEN]. Strings are not case + sensitive, and free insertion of linear white space is not permitted. + + sub-delims-sh = "!" / "$" / "'" / "(" / ")" / + "*" / "+" / "," + ;; Same as [URI-GEN] sub-delims, + ;; but without ";", "&" and "=". + + uchar = unreserved / sub-delims-sh / pct-encoded + + achar = uchar / "&" / "=" + ;; Same as [URI-GEN] 'unreserved / sub-delims / + ;; pct-encoded', but ";" is disallowed. + + bchar = achar / ":" / "@" / "/" + + + +Melnikov & Newman Standards Track [Page 17] + +RFC 5092 IMAP URL Scheme November 2007 + + + enc-auth-type = 1*achar + ; %-encoded version of [IMAP4] "auth-type" + + enc-mailbox = 1*bchar + ; %-encoded version of [IMAP4] "mailbox" + + enc-search = 1*bchar + ; %-encoded version of [IMAPABNF] + ; "search-program". Note that IMAP4 + ; literals may not be used in + ; a "search-program", i.e., only + ; quoted or non-synchronizing + ; literals (if the server supports + ; LITERAL+ [LITERAL+]) are allowed. + + enc-section = 1*bchar + ; %-encoded version of [IMAP4] "section-spec" + + enc-user = 1*achar + ; %-encoded version of [IMAP4] authorization + ; identity or "userid". + + imapurl = "imap://" iserver ipath-query + ; Defines an absolute IMAP URL + + ipath-query = ["/" [ icommand ]] + ; Corresponds to "path-abempty [ "?" query ]" + ; in [URI-GEN] + + Generic syntax for relative URLs is defined in Section 4.2 of + [URI-GEN]. For ease of implementation, the relative IMAP URL syntax + is defined below: + + imapurl-rel = inetwork-path + + / iabsolute-path + / irelative-path + / ipath-empty + + inetwork-path = "//" iserver ipath-query + ; Corresponds to '"//" authority path-abempty + ; [ "?" query ]' in [URI-GEN] + + iabsolute-path = "/" [ icommand ] + ; icommand, if present, MUST NOT start with '/'. + ; + ; Corresponds to 'path-absolute [ "?" query ]' + ; in [URI-GEN] + + + +Melnikov & Newman Standards Track [Page 18] + +RFC 5092 IMAP URL Scheme November 2007 + + + irelative-path = imessagelist / + imsg-or-part + ; Corresponds to 'path-noscheme [ "?" query ]' + ; in [URI-GEN] + + imsg-or-part = ( imailbox-ref "/" iuid-only ["/" isection-only] + ["/" ipartial-only] ) / + ( iuid-only ["/" isection-only] + ["/" ipartial-only] ) / + ( isection-only ["/" ipartial-only] ) / + ipartial-only + + ipath-empty = 0<pchar> + ; Zero characters. + ; The same-document reference. + + The following three rules are only used in the presence of the IMAP + [URLAUTH] extension: + + authimapurl = "imap://" iserver "/" imessagepart + ; Same as "imapurl" when "[icommand]" is + ; "imessagepart" + + authimapurlfull = authimapurl iurlauth + ; Same as "imapurl" when "[icommand]" is + ; "imessagepart iurlauth" + + authimapurlrump = authimapurl iurlauth-rump + + + enc-urlauth = 32*HEXDIG + + iurlauth = iurlauth-rump iua-verifier + + iua-verifier = ":" uauth-mechanism ":" enc-urlauth + + iurlauth-rump = [expire] ";URLAUTH=" access + + access = ("submit+" enc-user) / ("user+" enc-user) / + "authuser" / "anonymous" + + expire = ";EXPIRE=" date-time + ; date-time is defined in [DATETIME] + + uauth-mechanism = "INTERNAL" / 1*(ALPHA / DIGIT / "-" / ".") + ; Case-insensitive. + ; New mechanisms MUST be registered with IANA. + + + + +Melnikov & Newman Standards Track [Page 19] + +RFC 5092 IMAP URL Scheme November 2007 + + + iauth = ";AUTH=" ( "*" / enc-auth-type ) + + icommand = imessagelist / + imessagepart [iurlauth] + + imailbox-ref = enc-mailbox [uidvalidity] + + imessagelist = imailbox-ref [ "?" enc-search ] + ; "enc-search" is [URI-GEN] "query". + + imessagepart = imailbox-ref iuid [isection] [ipartial] + + ipartial = "/" ipartial-only + + ipartial-only = ";PARTIAL=" partial-range + + isection = "/" isection-only + + isection-only = ";SECTION=" enc-section + + iserver = [iuserinfo "@"] host [ ":" port ] + ; This is the same as "authority" defined + ; in [URI-GEN]. See [URI-GEN] for "host" + ; and "port" definitions. + + iuid = "/" iuid-only + + iuid-only = ";UID=" nz-number + ; See [IMAP4] for "nz-number" definition + + iuserinfo = enc-user [iauth] / [enc-user] iauth + ; conforms to the generic syntax of + ; "userinfo" as defined in [URI-GEN]. + + partial-range = number ["." nz-number] + ; partial FETCH. The first number is + ; the offset of the first byte, + ; the second number is the length of + ; the fragment. + + uidvalidity = ";UIDVALIDITY=" nz-number + ; See [IMAP4] for "nz-number" definition + + + + + + + + + +Melnikov & Newman Standards Track [Page 20] + +RFC 5092 IMAP URL Scheme November 2007 + + +12. IANA Considerations + + IANA has updated the "imap" definition in the "Uniform Resource + Identifier scheme registry" to point to this document. + + The registration template (as per [URI-REG]) is specified in Section + 12.1 of this document. + +12.1. IANA Registration of imap: URI Scheme + + This section provides the information required to register the imap: + URI scheme. + + URI scheme name: imap + + Status: permanent + + URI scheme syntax: + + See Section 11 of [RFC5092]. + + URI scheme semantics: + + The imap: URI scheme is used to designate IMAP servers, mailboxes, + messages, MIME bodies [MIME] and their parts, and search programs + on Internet hosts accessible using the IMAP protocol. + + There is no MIME type associated with this URI. + + Encoding considerations: + + See Section 8 of [RFC5092]. + + Applications/protocols that use this URI scheme name: + + The imap: URI is intended to be used by applications that might + need access to an IMAP mailstore. Such applications may include + (but are not limited to) IMAP-capable web browsers; IMAP clients + that wish to access a mailbox, message, or edit a message on the + server using [CATENATE]; [SUBMIT] clients and servers that are + requested to assemble a complete message on submission using + [BURL]. + + Interoperability considerations: + + A widely deployed IMAP client Netscape Mail (and possibly + Mozilla/Thunderbird/Seamonkey) uses a different imap: scheme + internally. + + + +Melnikov & Newman Standards Track [Page 21] + +RFC 5092 IMAP URL Scheme November 2007 + + + Security considerations: + + See Security Considerations (Section 10) of [RFC5092]. + + Contact: + + Alexey Melnikov <alexey.melnikov@isode.com> + + Author/Change controller: + + IESG + + References: + + [RFC5092] and [IMAP4]. + +13. References + +13.1. Normative References + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [IMAP4] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [IMAPABNF] Melnikov, A. and C. Daboo, "Collected Extensions to + IMAP4 ABNF", RFC 4466, April 2006. + + [ABNF] Crocker, D., Ed., and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", RFC 4234, October 2005. + + [MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail + Extensions (MIME) Part One: Format of Internet Message + Bodies", RFC 2045, November 1996. + + [URI-GEN] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform + Resource Identifier (URI): Generic Syntax", STD 66, RFC + 3986, January 2005. + + [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO + 10646", STD 63, RFC 3629, November 2003. + + [NAMESPACE] Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342, + May 1998. + + [LITERAL+] Myers, J., "IMAP4 non-synchronizing literals", RFC 2088, + January 1997. + + + +Melnikov & Newman Standards Track [Page 22] + +RFC 5092 IMAP URL Scheme November 2007 + + + [ANONYMOUS] Zeilenga, K., "Anonymous Simple Authentication and + Security Layer (SASL) Mechanism", RFC 4505, June 2006. + + [DATETIME] Klyne, G. and C. Newman, "Date and Time on the Internet: + Timestamps", RFC 3339, July 2002. + + [URLAUTH] Crispin, M., "Internet Message Access Protocol (IMAP) - + URLAUTH Extension", RFC 4467, May 2006. + +13.2. Informative References + + [SUBMIT] Gellens, R. and J. Klensin, "Message Submission for + Mail", RFC 4409, April 2006. + + [BURL] Newman, C., "Message Submission BURL Extension", RFC + 4468, May 2006. + + [CATENATE] Resnick, P., "Internet Message Access Protocol (IMAP) + CATENATE Extension", RFC 4469, April 2006. + + [SASL] Melnikov, A., Ed., and K. Zeilenga, Ed., "Simple + Authentication and Security Layer (SASL)", RFC 4422, + June 2006. + + [GSSAPI] Melnikov, A., Ed., "The Kerberos V5 ("GSSAPI") Simple + Authentication and Security Layer (SASL) Mechanism", RFC + 4752, November 2006. + + [DIGEST-MD5] Leach, P. and C. Newman, "Using Digest Authentication as + a SASL Mechanism", RFC 2831, May 2000. + + [URI-REG] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and + Registration Procedures for New URI Schemes", BCP 115, + RFC 4395, February 2006. + + + + + + + + + + + + + + + + + +Melnikov & Newman Standards Track [Page 23] + +RFC 5092 IMAP URL Scheme November 2007 + + +Appendix A. Sample Code + + Here is sample C source code to convert between URL paths and IMAP + mailbox names, taking into account mapping between IMAP's modified + UTF-7 [IMAP4] and hex-encoded UTF-8, which is more appropriate for + URLs. This code has not been rigorously tested nor does it + necessarily behave reasonably with invalid input, but it should serve + as a useful example. This code just converts the mailbox portion of + the URL and does not deal with parameters, query, or server + components of the URL. + +/* Copyright (C) The IETF Trust (2007). This version of + sample C code is part of RFC XXXX; see the RFC itself + for full legal notices. + + Regarding this sample C code (or any portion of it), the authors + make no guarantees and are not responsible for any damage + resulting from its use. The authors grant irrevocable permission + to anyone to use, modify, and distribute it in any way that does + not diminish the rights of anyone else to use, modify, and + distribute it, provided that redistributed derivative works do + not contain misleading author or version information. + + Derivative works need not be licensed under similar terms. + */ + +#include <stdio.h> +#include <string.h> + +/* hexadecimal lookup table */ +static const char hex[] = "0123456789ABCDEF"; + +#define XX 127 +/* + * Table for decoding hexadecimal in %encoding + */ +static const char index_hex[256] = { + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, + 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,XX,XX, XX,XX,XX,XX, + XX,10,11,12, 13,14,15,XX, XX,XX,XX,XX, XX,XX,XX,XX, + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, + XX,10,11,12, 13,14,15,XX, XX,XX,XX,XX, XX,XX,XX,XX, + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, + + + +Melnikov & Newman Standards Track [Page 24] + +RFC 5092 IMAP URL Scheme November 2007 + + + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, + XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, XX,XX,XX,XX, +}; +#define HEXCHAR(c) (index_hex[(unsigned char)(c)]) + +/* "gen-delims" excluding "/" but including "%" */ +#define GENERAL_DELIMS_NO_SLASH ":?#[]@" "%" + +/* "gen-delims" (excluding "/", but including "%") + plus subset of "sub-delims" */ +#define GENERAL_UNSAFE_NO_SLASH GENERAL_DELIMS_NO_SLASH ";&=+" +#define OTHER_UNSAFE " \"<>\\^`{|}" + +/* URL unsafe printable characters */ +static const char mailbox_url_unsafe[] = GENERAL_UNSAFE_NO_SLASH + OTHER_UNSAFE; + +/* UTF7 modified base64 alphabet */ +static const char base64chars[] = + "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,"; + +#define UNDEFINED 64 + +/* UTF16 definitions */ +#define UTF16MASK 0x03FFUL +#define UTF16SHIFT 10 +#define UTF16BASE 0x10000UL +#define UTF16HIGHSTART 0xD800UL +#define UTF16HIGHEND 0xDBFFUL +#define UTF16LOSTART 0xDC00UL +#define UTF16LOEND 0xDFFFUL + +/* Convert an IMAP mailbox to a URL path + * dst needs to have roughly 4 times the storage space of src + * Hex encoding can triple the size of the input + * UTF-7 can be slightly denser than UTF-8 + * (worst case: 8 octets UTF-7 becomes 9 octets UTF-8) + */ +void MailboxToURL(char *dst, char *src) +{ + unsigned char c, i, bitcount; + unsigned long ucs4, utf16, bitbuf; + unsigned char base64[256], utf8[6]; + + /* initialize modified base64 decoding table */ + + + +Melnikov & Newman Standards Track [Page 25] + +RFC 5092 IMAP URL Scheme November 2007 + + + memset(base64, UNDEFINED, sizeof (base64)); + for (i = 0; i < sizeof (base64chars); ++i) { + base64[(int) base64chars[i]] = i; + } + + /* loop until end of string */ + while (*src != '\0') { + c = *src++; + /* deal with literal characters and &- */ + if (c != '&' || *src == '-') { + /* NB: There are no "URL safe" characters after the '~' */ + if (c < ' ' || c > '~' || + strchr(mailbox_url_unsafe, c) != NULL) { + /* hex encode if necessary */ + dst[0] = '%'; + dst[1] = hex[c >> 4]; + dst[2] = hex[c & 0x0f]; + dst += 3; + } else { + /* encode literally */ + *dst++ = c; + } + /* skip over the '-' if this is an &- sequence */ + if (c == '&') ++src; + + } else { + /* convert modified UTF-7 -> UTF-16 -> UCS-4 -> UTF-8 -> HEX */ + bitbuf = 0; + bitcount = 0; + ucs4 = 0; + while ((c = base64[(unsigned char) *src]) != UNDEFINED) { + ++src; + bitbuf = (bitbuf << 6) | c; + bitcount += 6; + /* enough bits for a UTF-16 character? */ + if (bitcount >= 16) { + bitcount -= 16; + utf16 = (bitcount ? bitbuf >> bitcount + : bitbuf) & 0xffff; + /* convert UTF16 to UCS4 */ + if + (utf16 >= UTF16HIGHSTART && utf16 <= UTF16HIGHEND) { + ucs4 = (utf16 - UTF16HIGHSTART) << UTF16SHIFT; + continue; + } else if + (utf16 >= UTF16LOSTART && utf16 <= UTF16LOEND) { + ucs4 += utf16 - UTF16LOSTART + UTF16BASE; + } else { + + + +Melnikov & Newman Standards Track [Page 26] + +RFC 5092 IMAP URL Scheme November 2007 + + + ucs4 = utf16; + } + /* convert UTF-16 range of UCS4 to UTF-8 */ + if (ucs4 <= 0x7fUL) { + utf8[0] = (unsigned char) ucs4; + i = 1; + } else if (ucs4 <= 0x7ffUL) { + utf8[0] = 0xc0 | (unsigned char) (ucs4 >> 6); + utf8[1] = 0x80 | (unsigned char) (ucs4 & 0x3f); + i = 2; + } else if (ucs4 <= 0xffffUL) { + utf8[0] = 0xe0 | (unsigned char) (ucs4 >> 12); + utf8[1] = 0x80 | (unsigned char) ((ucs4 >> 6) & 0x3f); + utf8[2] = 0x80 | (unsigned char) (ucs4 & 0x3f); + i = 3; + } else { + utf8[0] = 0xf0 | (unsigned char) (ucs4 >> 18); + utf8[1] = 0x80 | (unsigned char) ((ucs4 >> 12) & 0x3f); + utf8[2] = 0x80 | (unsigned char) ((ucs4 >> 6) & 0x3f); + utf8[3] = 0x80 | (unsigned char) (ucs4 & 0x3f); + i = 4; + } + /* convert utf8 to hex */ + for (c = 0; c < i; ++c) { + dst[0] = '%'; + dst[1] = hex[utf8[c] >> 4]; + dst[2] = hex[utf8[c] & 0x0f]; + dst += 3; + } + } + } + /* skip over trailing '-' in modified UTF-7 encoding */ + if (*src == '-') ++src; + } + } + /* terminate destination string */ + *dst = '\0'; +} + +/* Convert hex coded UTF-8 URL path to modified UTF-7 IMAP mailbox + * dst should be about twice the length of src to deal with non-hex + * coded URLs + */ +int URLtoMailbox(char *dst, char *src) +{ + unsigned int utf8pos = 0; + unsigned int utf8total, i, c, utf7mode, bitstogo, utf16flag; + unsigned long ucs4 = 0, bitbuf = 0; + + + +Melnikov & Newman Standards Track [Page 27] + +RFC 5092 IMAP URL Scheme November 2007 + + + utf7mode = 0; /* is the output UTF7 currently in base64 mode? */ + utf8total = 0; /* how many octets is the current input UTF-8 char; + 0 == between characters */ + bitstogo = 0; /* bits that need to be encoded into base64; if + bitstogo != 0 then utf7mode == 1 */ + while ((c = (unsigned char)*src) != '\0') { + ++src; + /* undo hex-encoding */ + if (c == '%' && src[0] != '\0' && src[1] != '\0') { + c = HEXCHAR(src[0]); + i = HEXCHAR(src[1]); + if (c == XX || i == XX) { + return 0; + } else { + c = (char)((c << 4) | i); + } + src += 2; + } + /* normal character? */ + if (c >= ' ' && c <= '~') { + /* switch out of UTF-7 mode */ + if (utf7mode) { + if (bitstogo) { + *dst++ = base64chars[(bitbuf << (6 - bitstogo)) & 0x3F]; + } + *dst++ = '-'; + utf7mode = 0; + bitstogo = bitbuf = 0; + } + *dst++ = c; + /* encode '&' as '&-' */ + if (c == '&') { + *dst++ = '-'; + } + continue; + } + /* switch to UTF-7 mode */ + if (!utf7mode) { + *dst++ = '&'; + utf7mode = 1; + } + /* Encode US-ASCII characters as themselves */ + if (c < 0x80) { + ucs4 = c; + utf8total = 1; + } else if (utf8total) { + /* this is a subsequent octet of a multi-octet character */ + /* save UTF8 bits into UCS4 */ + + + +Melnikov & Newman Standards Track [Page 28] + +RFC 5092 IMAP URL Scheme November 2007 + + + ucs4 = (ucs4 << 6) | (c & 0x3FUL); + if (++utf8pos < utf8total) { + continue; + } + } else { + /* this is the first octet of a multi-octet character */ + utf8pos = 1; + if (c < 0xE0) { + utf8total = 2; + ucs4 = c & 0x1F; + } else if (c < 0xF0) { + utf8total = 3; + ucs4 = c & 0x0F; + } else { + /* NOTE: can't convert UTF8 sequences longer than 4 */ + utf8total = 4; + ucs4 = c & 0x03; + } + continue; + } + /* Finished with UTF-8 character. Make sure it isn't an + overlong sequence. If it is, return failure. */ + if ((ucs4 < 0x80 && utf8total > 1) || + (ucs4 < 0x0800 && utf8total > 2) || + (ucs4 < 0x00010000 && utf8total > 3) || + (ucs4 < 0x00200000 && utf8total > 4) || + (ucs4 < 0x04000000 && utf8total > 5) || + (ucs4 < 0x80000000 && utf8total > 6)) { + return 0; + } + /* loop to split ucs4 into two utf16 chars if necessary */ + utf8total = 0; + do { + if (ucs4 >= UTF16BASE) { + ucs4 -= UTF16BASE; + bitbuf = (bitbuf << 16) | ((ucs4 >> UTF16SHIFT) + + UTF16HIGHSTART); + ucs4 = (ucs4 & UTF16MASK) + UTF16LOSTART; + utf16flag = 1; + } else { + bitbuf = (bitbuf << 16) | ucs4; + utf16flag = 0; + } + bitstogo += 16; + /* spew out base64 */ + while (bitstogo >= 6) { + bitstogo -= 6; + *dst++ = base64chars[(bitstogo ? (bitbuf >> bitstogo) + + + +Melnikov & Newman Standards Track [Page 29] + +RFC 5092 IMAP URL Scheme November 2007 + + + : bitbuf) + & 0x3F]; + } + } while (utf16flag); + } + /* if in UTF-7 mode, finish in ASCII */ + if (utf7mode) { + if (bitstogo) { + *dst++ = base64chars[(bitbuf << (6 - bitstogo)) & 0x3F]; + } + *dst++ = '-'; + } + /* tie off string */ + *dst = '\0'; + return 1; +} + +Appendix B. List of Changes since RFC 2192 + + Updated boilerplate, list of editor's, etc. + Updated references. + Updated ABNF not to use _, to use SP instead of SPACE, etc. + Updated example domains to use example.org. + Fixed ABNF error in "imessagelist" non-terminal. + Updated ABNF, due to changes in RFC 3501, RFC 4466, and RFC 3986. + Renamed "iuserauth" non-terminal to <iuserinfo>. + Clarified that the userinfo component describes both authorization + identity and mailbox naming scope. + Allow for non-synchronizing literals in "enc-search". + Added "ipartial" specifier that denotes a partial FETCH. + Moved URLAUTH text from RFC 4467 to this document. + Updated ABNF for the whole server to allow missing trailing "/" + (e.g., "imap://imap.example.com" is now valid and is the same as + "imap://imap.example.com/"). + Clarified how relative-path references are constructed. + Added more examples demonstrating relative-path references. + Added rules for relative URLs and restructured ABNF as the result. + Removed text on use of relative URLs in MHTML. + Added examples demonstrating security considerations when resolving + URLs. + Recommend usage of STARTTLS/SASL security layer to protect + confidential data. + Removed some advices about connection reuse that were incorrect. + Removed URLs referencing a list of mailboxes, as this feature + hasn't seen any deployments. + Clarified that user name "anonymous" is case-insensitive. + + + + + +Melnikov & Newman Standards Track [Page 30] + +RFC 5092 IMAP URL Scheme November 2007 + + +Appendix C. List of Changes since RFC 4467 + + Renamed <mechanism> to <uauth-mechanism>. Restructured ABNF. + +Appendix D. Acknowledgments + + Text describing URLAUTH was lifted from [URLAUTH] by Mark Crispin. + + Stephane H. Maes contributed some ideas to this document; he also + co-edited early versions of this document. + + The editors would like to thank Mark Crispin, Ken Murchison, Ted + Hardie, Zoltan Ordogh, Dave Cridland, Kjetil Torgrim Homme, Lisa + Dusseault, Spencer Dawkins, Filip Navara, Shawn M. Emery, Sam + Hartman, Russ Housley, and Lars Eggert for the time they devoted to + reviewing this document and/or for the comments received. + +Authors' Addresses + + Chris Newman (Author/Editor) + Sun Microsystems + 3401 Centrelake Dr., Suite 410 + Ontario, CA 91761 + EMail: chris.newman@sun.com + + Alexey Melnikov (Editor) + Isode Limited + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex + TW12 2BX, UK + EMail: Alexey.Melnikov@isode.com + URI: http://www.melnikov.ca/ + + + + + + + + + + + + + + + + + + +Melnikov & Newman Standards Track [Page 31] + +RFC 5092 IMAP URL Scheme November 2007 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2007). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Melnikov & Newman Standards Track [Page 32] + diff --git a/imap/docs/rfc/rfc5161.txt b/imap/docs/rfc/rfc5161.txt new file mode 100644 index 00000000..13bbbf74 --- /dev/null +++ b/imap/docs/rfc/rfc5161.txt @@ -0,0 +1,395 @@ + + + + + + +Network Working Group A. Gulbrandsen, Ed. +Request for Comments: 5161 Oryx Mail Systems GmbH +Category: Standards Track A. Melnikov, Ed. + Isode Limited + March 2008 + + + The IMAP ENABLE Extension + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + Most IMAP extensions are used by the client when it wants to and the + server supports it. However, a few extensions require the server to + know whether a client supports that extension. The ENABLE extension + allows an IMAP client to say which extensions it supports. + +1. Overview + + Several IMAP extensions allow the server to return unsolicited + responses specific to these extensions in certain circumstances. + However, servers cannot send those unsolicited responses until they + know that the clients support such extensions and thus won't choke on + the extension response data. + + Up until now, extensions have typically stated that a server cannot + send the unsolicited responses until after the client has used a + command with the extension data (i.e., at that point the server knows + the client is aware of the extension). CONDSTORE ([RFC4551]), + ANNOTATE ([ANNOTATE]), and some extensions under consideration at the + moment use various commands to enable server extensions. For + example, CONDSTORE uses a SELECT or FETCH parameter, and ANNOTATE + uses a side effect of FETCH. + + The ENABLE extension provides an explicit indication from the client + that it supports particular extensions. This is done using a new + ENABLE command. + + An IMAP server that supports ENABLE advertises this by including the + word ENABLE in its capability list. + + + + +Gulbrandsen & Melnikov Standards Track [Page 1] + +RFC 5161 The IMAP ENABLE Extension March 2008 + + + Most IMAP extensions do not require the client to enable the + extension in any way. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + + Formal syntax is defined by [RFC5234] and [RFC3501]. + + Example lines prefaced by "C:" are sent by the client and ones + prefaced by "S:" by the server. The five characters [...] means that + something has been elided. + +3. Protocol Changes + +3.1. The ENABLE Command + + Arguments: capability names + + Result: OK: Relevant capabilities enabled + BAD: No arguments, or syntax error in an argument + + The ENABLE command takes a list of capability names, and requests the + server to enable the named extensions. Once enabled using ENABLE, + each extension remains active until the IMAP connection is closed. + For each argument, the server does the following: + + - If the argument is not an extension known to the server, the server + MUST ignore the argument. + + - If the argument is an extension known to the server, and it is not + specifically permitted to be enabled using ENABLE, the server MUST + ignore the argument. (Note that knowing about an extension doesn't + necessarily imply supporting that extension.) + + - If the argument is an extension that is supported by the server and + that needs to be enabled, the server MUST enable the extension for + the duration of the connection. At present, this applies only to + CONDSTORE ([RFC4551]). Note that once an extension is enabled, + there is no way to disable it. + + If the ENABLE command is successful, the server MUST send an untagged + ENABLED response (see Section 3.2). + + + + + + +Gulbrandsen & Melnikov Standards Track [Page 2] + +RFC 5161 The IMAP ENABLE Extension March 2008 + + + Clients SHOULD only include extensions that need to be enabled by the + server. At the time of publication, CONDSTORE is the only such + extension (i.e., ENABLE CONDSTORE is an additional "CONDSTORE + enabling command" as defined in [RFC4551]). Future RFCs may add to + this list. + + The ENABLE command is only valid in the authenticated state (see + [RFC3501]), before any mailbox is selected. Clients MUST NOT issue + ENABLE once they SELECT/EXAMINE a mailbox; however, server + implementations don't have to check that no mailbox is selected or + was previously selected during the duration of a connection. + + The ENABLE command can be issued multiple times in a session. It is + additive; i.e., "ENABLE a b", followed by "ENABLE c" is the same as a + single command "ENABLE a b c". When multiple ENABLE commands are + issued, each corresponding ENABLED response SHOULD only contain + extensions enabled by the corresponding ENABLE command. + + There are no limitations on pipelining ENABLE. For example, it is + possible to send ENABLE and then immediately SELECT, or a LOGIN + immediately followed by ENABLE. + + The server MUST NOT change the CAPABILITY list as a result of + executing ENABLE; i.e., a CAPABILITY command issued right after an + ENABLE command MUST list the same capabilities as a CAPABILITY + command issued before the ENABLE command. This is demonstrated in + the following example: + + C: t1 CAPABILITY + S: * CAPABILITY IMAP4rev1 ID LITERAL+ ENABLE X-GOOD-IDEA + S: t1 OK foo + C: t2 ENABLE CONDSTORE X-GOOD-IDEA + S: * ENABLED X-GOOD-IDEA + S: t2 OK foo + C: t3 CAPABILITY + S: * CAPABILITY IMAP4rev1 ID LITERAL+ ENABLE X-GOOD-IDEA + S: t3 OK foo again + + In the following example, the client enables CONDSTORE: + + C: a1 ENABLE CONDSTORE + S: * ENABLED CONDSTORE + S: a1 OK Conditional Store enabled + + + + + + + + +Gulbrandsen & Melnikov Standards Track [Page 3] + +RFC 5161 The IMAP ENABLE Extension March 2008 + + +3.2. The ENABLED Response + + Contents: capability listing + + The ENABLED response occurs as a result of an ENABLE command. The + capability listing contains a space-separated listing of capability + names that the server supports and that were successfully enabled. + The ENABLED response may contain no capabilities, which means that no + extensions listed by the client were successfully enabled. + +3.3. Note to Designers of Extensions That May Use the ENABLE Command + + Designers of IMAP extensions are discouraged from creating extensions + that require ENABLE unless there is no good alternative design. + Specifically, extensions that cause potentially incompatible behavior + changes to deployed server responses (and thus benefit from ENABLE) + have a higher complexity cost than extensions that do not. + +4. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [RFC5234] including the core + rules in Appendix B.1. [RFC3501] defines the non-terminals + "capability" and "command-any". + + Except as noted otherwise, all alphabetic characters are + case-insensitive. The use of upper or lower case characters to + define token strings is for editorial clarity only. Implementations + MUST accept these strings in a case-insensitive fashion. + + capability =/ "ENABLE" + + command-any =/ "ENABLE" 1*(SP capability) + + response-data =/ "*" SP enable-data CRLF + + enable-data = "ENABLED" *(SP capability) + +5. Security Considerations + + It is believed that this extension doesn't add any security + considerations that are not already present in the base IMAP protocol + [RFC3501]. + +6. IANA Considerations + + The IANA has added ENABLE to the IMAP4 Capabilities Registry. + + + + +Gulbrandsen & Melnikov Standards Track [Page 4] + +RFC 5161 The IMAP ENABLE Extension March 2008 + + +7. Acknowledgments + + The editors would like to thank Randy Gellens, Chris Newman, Peter + Coates, Dave Cridland, Mark Crispin, Ned Freed, Dan Karp, Cyrus + Daboo, Ken Murchison, and Eric Burger for comments and corrections. + However, this doesn't necessarily mean that they endorse this + extension, agree with all details, or are responsible for errors + introduced by the editors. + +8. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", STD 68, RFC 5234, January + 2008. + + [RFC4551] Melnikov, A. and S. Hole, "IMAP Extension for Conditional + STORE Operation or Quick Flag Changes Resynchronization", + RFC 4551, June 2006. + +9. Informative References + + [ANNOTATE] Daboo, C. and R. Gellens, "IMAP ANNOTATE Extension", Work + in Progress, August 2006. + + + + + + + + + + + + + + + + + + + + + + +Gulbrandsen & Melnikov Standards Track [Page 5] + +RFC 5161 The IMAP ENABLE Extension March 2008 + + +Editors' Addresses + + Arnt Gulbrandsen + Oryx Mail Systems GmbH + Schweppermannstr. 8 + D-81671 Muenchen + Germany + + Fax: +49 89 4502 9758 + EMail: arnt@oryx.com + + + Alexey Melnikov + Isode Ltd + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: Alexey.Melnikov@isode.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Gulbrandsen & Melnikov Standards Track [Page 6] + +RFC 5161 The IMAP ENABLE Extension March 2008 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2008). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Gulbrandsen & Melnikov Standards Track [Page 7] + diff --git a/imap/docs/rfc/rfc5162.txt b/imap/docs/rfc/rfc5162.txt new file mode 100644 index 00000000..305c54fb --- /dev/null +++ b/imap/docs/rfc/rfc5162.txt @@ -0,0 +1,1291 @@ + + + + + + +Network Working Group A. Melnikov +Request for Comments: 5162 D. Cridland +Category: Standards Track Isode Ltd + C. Wilson + Nokia + March 2008 + + + IMAP4 Extensions for Quick Mailbox Resynchronization + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + This document defines an IMAP4 extension, which gives an IMAP client + the ability to quickly resynchronize any previously opened mailbox as + part of the SELECT command, without the need for server-side state or + additional client round-trips. This extension also introduces a new + response that allows for a more compact representation of a list of + expunged messages (and always includes the Unique Identifiers (UIDs) + expunged). + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov, et al. Standards Track [Page 1] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + +Table of Contents + + 1. Introduction and Overview . . . . . . . . . . . . . . . . . . 2 + 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4 + 3. IMAP Protocol Changes . . . . . . . . . . . . . . . . . . . . 4 + 3.1. QRESYNC Parameter to SELECT/EXAMINE . . . . . . . . . . . 4 + 3.2. VANISHED UID FETCH Modifier . . . . . . . . . . . . . . . 8 + 3.3. EXPUNGE Command . . . . . . . . . . . . . . . . . . . . . 10 + 3.4. CLOSE Command . . . . . . . . . . . . . . . . . . . . . . 11 + 3.5. UID EXPUNGE Command . . . . . . . . . . . . . . . . . . . 11 + 3.6. VANISHED Response . . . . . . . . . . . . . . . . . . . . 12 + 3.7. CLOSED Response Code . . . . . . . . . . . . . . . . . . . 15 + 4. Server Implementation Considerations . . . . . . . . . . . . . 15 + 4.1. Server Implementations That Don't Store Extra State . . . 15 + 4.2. Server Implementations Storing Minimal State . . . . . . . 16 + 4.3. Additional State Required on the Server . . . . . . . . . 16 + 5. Updated Synchronization Sequence . . . . . . . . . . . . . . . 17 + 6. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 19 + 7. Security Considerations . . . . . . . . . . . . . . . . . . . 20 + 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 + 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21 + 10.1. Normative References . . . . . . . . . . . . . . . . . . . 21 + 10.2. Informative References . . . . . . . . . . . . . . . . . . 22 + +1. Introduction and Overview + + The [CONDSTORE] extension gives a disconnected client the ability to + quickly resynchronize IMAP flag changes for previously seen messages. + This can be done using the CHANGEDSINCE FETCH modifier once a mailbox + is opened. In order for the client to discover which messages have + been expunged, the client still has to issue a UID FETCH or a UID + SEARCH command. This document defines an extension to [CONDSTORE] + that allows a reconnecting client to perform full resynchronization, + including discovery of expunged messages, in a single round-trip. + This extension also introduces a new response, VANISHED, that allows + for a more compact representation of a list of expunged messages. + + This extension can be useful for mobile clients that can experience + frequent disconnects caused by environmental factors (battery life, + signal strength, etc.). Such clients need a way to quickly reconnect + to the IMAP server, while minimizing delay experienced by the user as + well as the amount of traffic (and hence the expense) generated by + resynchronization. + + + + + + + +Melnikov, et al. Standards Track [Page 2] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + By extending the SELECT command to perform the additional + resynchronization, this also allows clients to reduce concurrent + connections to the IMAP server held purely for the sake of avoiding + the resynchronization. + + The quick resync IMAP extension is present if an IMAP4 server returns + "QRESYNC" as one of the supported capabilities to the CAPABILITY + command. + + Servers supporting this extension MUST implement and advertise + support for the [ENABLE] IMAP extension. Also, the presence of the + "QRESYNC" capability implies support for the [CONDSTORE] IMAP + extension even if the CONDSTORE capability isn't advertised. A + server compliant with this specification is REQUIREd to support + "ENABLE QRESYNC" and "ENABLE QRESYNC CONDSTORE" (which are "CONDSTORE + enabling commands", as defined in [CONDSTORE], and have identical + results), but there is no requirement for a compliant server to + support "ENABLE CONDSTORE" by itself. The "ENABLE QRESYNC"/"ENABLE + QRESYNC CONDSTORE" command also tells the server that it SHOULD start + sending VANISHED responses (see Section 3.6) instead of EXPUNGE + responses. This change remains in effect until the connection is + closed. + + For compatibility with clients that only support the [CONDSTORE] IMAP + extension, servers SHOULD advertise CONDSTORE in the CAPABILITY + response as well. + + A client making use of this extension MUST issue "ENABLE QRESYNC" + once it is authenticated. A server MUST respond with a tagged BAD + response if the QRESYNC parameter to the SELECT/EXAMINE command or + the VANISHED UID FETCH modifier is specified and the client hasn't + issued "ENABLE QRESYNC" in the current connection. + + This document puts additional requirements on a server implementing + the [CONDSTORE] extension. Each mailbox that supports persistent + storage of mod-sequences, i.e., for which the server has sent a + HIGHESTMODSEQ untagged OK response code on a successful SELECT/ + EXAMINE, MUST increment the per-mailbox mod-sequence when one or more + messages are expunged due to EXPUNGE, UID EXPUNGE or CLOSE; the + server MUST associate the incremented mod-sequence with the UIDs of + the expunged messages. + + A client that supports CONDSTORE but not this extension might + resynchronize a mailbox and discover that its HIGHESTMODSEQ has + increased from the value cached by the client. If the increase is + only due to messages having been expunged since the client last + synchronized, the client is likely to send a FETCH ... CHANGEDSINCE + command that returns no data. Thus, a client that supports CONDSTORE + + + +Melnikov, et al. Standards Track [Page 3] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + but not this extension might incur a penalty of an unneeded round- + trip when resynchronizing some mailboxes (those that have had + messages expunged but no flag changes since the last + synchronization). + + This extra round-trip is only incurred by clients that support + CONDSTORE but not this extension, and only when a mailbox has had + messages expunged but no flag changes to non-expunged messages. + Since CONDSTORE is a relatively new extension, it is thought likely + that clients that support it will also support this extension. + +2. Requirements Notation + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. If a single "C:" or "S:" label applies to + multiple lines, then the line breaks between those lines are for + editorial clarity only and are not part of the actual protocol + exchange. The five characters [...] means that something has been + elided. + + Understanding of the IMAP message sequence numbers and UIDs and the + EXPUNGE response [RFC3501] is essential when reading this document. + +3. IMAP Protocol Changes + +3.1. QRESYNC Parameter to SELECT/EXAMINE + + The Quick Resynchronization parameter to SELECT/EXAMINE commands has + four arguments: + + o the last known UIDVALIDITY, + + o the last known modification sequence, + + o the optional set of known UIDs, and + + o an optional parenthesized list of known sequence ranges and their + corresponding UIDs. + + A server MUST respond with a tagged BAD response if the Quick + Resynchronization parameter to SELECT/EXAMINE command is specified + and the client hasn't issued "ENABLE QRESYNC" in the current + connection. + + + + +Melnikov, et al. Standards Track [Page 4] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + Before opening the specified mailbox, the server verifies all + arguments for syntactic validity. If any parameter is not + syntactically valid, the server returns the tagged BAD response, and + the mailbox remains unselected. Once the check is done, the server + opens the mailbox as if no SELECT/EXAMINE parameters are specified + (this is subject to processing of other parameters as defined in + other extensions). In particular this means that the server MUST + send all untagged responses as specified in Sections 6.3.1 and 6.3.2 + of [RFC3501]. + + After that, the server checks the UIDVALIDITY value provided by the + client. If the provided UIDVALIDITY doesn't match the UIDVALIDITY + for the mailbox being opened, then the server MUST ignore the + remaining parameters and behave as if no dynamic message data + changed. The client can discover this situation by comparing the + UIDVALIDITY value returned by the server. This behavior allows the + client not to synchronize the mailbox or decide on the best + synchronization strategy. + + Example: Attempting to resynchronize INBOX, but the provided + UIDVALIDITY parameter doesn't match the current UIDVALIDITY + value. + + C: A02 SELECT INBOX (QRESYNC (67890007 20050715194045000 + 41,43:211,214:541)) + S: * 464 EXISTS + S: * 3 RECENT + S: * OK [UIDVALIDITY 3857529045] UIDVALIDITY + S: * OK [UIDNEXT 550] Predicted next UID + S: * OK [HIGHESTMODSEQ 90060128194045007] + S: * OK [UNSEEN 12] Message 12 is first unseen + S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen) + S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft + \Deleted \Seen \*)] Permanent flags + S: A02 OK [READ-WRITE] Sorry, UIDVALIDITY mismatch + + Modification Sequence and UID Parameters: + + A server that doesn't support the persistent storage of mod-sequences + for the mailbox MUST send the OK untagged response including the + NOMODSEQ response code with every successful SELECT or EXAMINE + command, as described in [CONDSTORE]. Such a server doesn't need to + remember mod-sequences for expunged messages in the mailbox. It MUST + ignore the remaining parameters and behave as if no dynamic message + data changed. + + If the provided UIDVALIDITY matches that of the selected mailbox, the + server then checks the last known modification sequence. + + + +Melnikov, et al. Standards Track [Page 5] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + The server sends the client any pending flag changes (using FETCH + responses that MUST contain UIDs) and expunges those that have + occurred in this mailbox since the provided modification sequence. + + If the list of known UIDs was also provided, the server should only + report flag changes and expunges for the specified messages. If the + client did not provide the list of UIDs, the server acts as if the + client has specified "1:<maxuid>", where <maxuid> is the mailbox's + UIDNEXT value minus 1. If the mailbox is empty and never had any + messages in it, then lack of the list of UIDs is interpreted as an + empty set of UIDs. + + Thus, the client can process just these pending events and need not + perform a full resynchronization. Without the message sequence + number matching information, the result of this step is semantically + equivalent to the client issuing: + tag1 UID FETCH "known-uids" (FLAGS) (CHANGEDSINCE + "mod-sequence-value" VANISHED) + + Example: + C: A03 SELECT INBOX (QRESYNC (67890007 + 90060115194045000 41,43:211,214:541)) + S: * OK [CLOSED] + S: * 314 EXISTS + S: * 15 RECENT + S: * OK [UIDVALIDITY 67890007] UIDVALIDITY + S: * OK [UIDNEXT 567] Predicted next UID + S: * OK [HIGHESTMODSEQ 90060115205545359] + S: * OK [UNSEEN 7] There are some unseen messages in the mailbox + S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen) + S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft + \Deleted \Seen \*)] Permanent flags + S: * VANISHED (EARLIER) 41,43:116,118,120:211,214:540 + S: * 49 FETCH (UID 117 FLAGS (\Seen \Answered) MODSEQ + (90060115194045001)) + S: * 50 FETCH (UID 119 FLAGS (\Draft $MDNSent) MODSEQ + (90060115194045308)) + S: ... + S: * 100 FETCH (UID 541 FLAGS (\Seen $Forwarded) MODSEQ + (90060115194045001)) + S: A03 OK [READ-WRITE] mailbox selected + + Message sequence match data: + + A client MAY provide a parenthesized list of a message sequence set + and the corresponding UID sets. Both MUST be provided in ascending + order. The server uses this data to restrict the range for which it + provides expunged message information. + + + +Melnikov, et al. Standards Track [Page 6] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + Conceptually, the client provides a small sample of sequence numbers + for which it knows the corresponding UIDs. The server then compares + each sequence number and UID pair the client provides with the + current state of the mailbox. If a pair matches, then the client + knows of any expunges up to, and including, the message, and thus + will not include that range in the VANISHED response, even if the + "mod-sequence-value" provided by the client is too old for the server + to have data of when those messages were expunged. + + Thus, if the Nth message number in the first set in the list is 4, + and the Nth UID in the second set in the list is 8, and the mailbox's + fourth message has UID 8, then no UIDs equal to or less than 8 are + present in the VANISHED response. If the (N+1)th message number is + 12, and the (N+1)th UID is 24, and the (N+1)th message in the mailbox + has UID 25, then the lowest UID included in the VANISHED response + would be 9. + + In the following two examples, the server is unable to remember + expunges at all, and only UIDs with messages divisible by three are + present in the mailbox. In the first example, the client does not + use the fourth parameter; in the second, it provides it. This + example is somewhat extreme, but shows that judicious usage of the + sequence match data can save a substantial amount of bandwidth. + + Example: + C: A04 SELECT INBOX (QRESYNC (67890007 + 90060115194045000 1:29997)) + S: * 10003 EXISTS + S: * 5 RECENT + S: * OK [UIDVALIDITY 67890007] UIDVALIDITY + S: * OK [UIDNEXT 30013] Predicted next UID + S: * OK [HIGHESTMODSEQ 90060115205545359] + S: * OK [UNSEEN 7] There are some unseen messages in the mailbox + S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen) + S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft + \Deleted \Seen \*)] Permanent flags + S: * VANISHED (EARLIER) 1:2,4:5,7:8,10:11,13:14 [...] + 29998:29999,30001:30002,30004:30005,30007:30008 + S: * 9889 FETCH (UID 29667 FLAGS (\Seen \Answered) MODSEQ + (90060115194045027)) + S: * 9890 FETCH (UID 29670 FLAGS (\Draft $MDNSent) MODSEQ + (90060115194045028)) + S: ... + S: * 9999 FETCH (UID 29997 FLAGS (\Seen $Forwarded) MODSEQ + (90060115194045031)) + S: A04 OK [READ-WRITE] mailbox selected + + + + + +Melnikov, et al. Standards Track [Page 7] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + Example: + C: B04 SELECT INBOX (QRESYNC (67890007 + 90060115194045000 1:29997 (5000,7500,9000,9990:9999 15000, + 22500,27000,29970,29973,29976,29979,29982,29985,29988,29991, + 29994,29997))) + S: * 10003 EXISTS + S: * 5 RECENT + S: * OK [UIDVALIDITY 67890007] UIDVALIDITY + S: * OK [UIDNEXT 30013] Predicted next UID + S: * OK [HIGHESTMODSEQ 90060115205545359] + S: * OK [UNSEEN 7] There are some unseen messages in the mailbox + S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen) + S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft + \Deleted \Seen \*)] Permanent flags + S: * VANISHED (EARLIER) 29998:29999,30001:30002,30004:30005,30007: + 30008 + S: * 9889 FETCH (UID 29667 FLAGS (\Seen \Answered) MODSEQ + (90060115194045027)) + S: * 9890 FETCH (UID 29670 FLAGS (\Draft $MDNSent) MODSEQ + (90060115194045028)) + S: ... + S: * 9999 FETCH (UID 29997 FLAGS (\Seen $Forwarded) MODSEQ + (90060115194045031)) + S: B04 OK [READ-WRITE] mailbox selected + +3.2. VANISHED UID FETCH Modifier + + [IMAPABNF] has extended the syntax of the FETCH and UID FETCH + commands to include an optional FETCH modifier. This document + defines a new UID FETCH modifier: VANISHED. + + Note, that the VANISHED UID FETCH modifier is NOT allowed with a + FETCH command. The server MUST return a tagged BAD response if this + response is specified as a modifier to the FETCH command. + + A server MUST respond with a tagged BAD response if the VANISHED UID + FETCH modifier is specified and the client hasn't issued "ENABLE + QRESYNC" in the current connection. + + The VANISHED UID FETCH modifier MUST only be specified together with + the CHANGEDSINCE UID FETCH modifier. + + The VANISHED UID FETCH modifier instructs the server to report those + messages from the UID set parameter that have been expunged and whose + associated mod-sequence is larger than the specified mod-sequence. + That is, the client requests to be informed of messages from the + specified set that were expunged since the specified mod-sequence. + Note that the mod-sequence(s) associated with these messages were + + + +Melnikov, et al. Standards Track [Page 8] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + updated when the messages were expunged (as described above). The + expunged messages are reported using the VANISHED response as + described in Section 3.6, which MUST contain the EARLIER tag. Any + VANISHED (EARLIER) responses MUST be returned before any FETCH + responses, as otherwise the client might get confused about how + message numbers map to UIDs. + + Note: A server that receives a mod-sequence smaller than <minmodseq>, + where <minmodseq> is the value of the smallest expunged mod-sequence + it remembers minus one, MUST behave as if it was requested to report + all expunged messages from the provided UID set parameter. + + Example 1: Without the VANISHED UID FETCH modifier, a CONDSTORE-aware + client [CONDSTORE] needs to issue separate commands to learn of flag + changes and expunged messages since the last synchronization: + + C: s100 UID FETCH 300:500 (FLAGS) (CHANGEDSINCE 12345) + S: * 1 FETCH (UID 404 MODSEQ (65402) FLAGS (\Seen)) + S: * 2 FETCH (UID 406 MODSEQ (75403) FLAGS (\Deleted)) + S: * 4 FETCH (UID 408 MODSEQ (29738) FLAGS ($NoJunk + $AutoJunk $MDNSent)) + S: s100 OK FETCH completed + C: s101 UID SEARCH 300:500 + S: * SEARCH 404 406 407 408 410 412 + S: s101 OK search completed + + Where 300 and 500 are the lowest and highest UIDs from client's + cache. The second SEARCH response tells the client that the messages + with UIDs 407, 410, and 412 are still present, but their flags + haven't changed since the specified modification sequence. + + Using the VANISHED UID FETCH modifier, it is sufficient to issue only + a single command: + + C: s100 UID FETCH 300:500 (FLAGS) (CHANGEDSINCE 12345 + VANISHED) + S: * VANISHED (EARLIER) 300:310,405,411 + S: * 1 FETCH (UID 404 MODSEQ (65402) FLAGS (\Seen)) + S: * 2 FETCH (UID 406 MODSEQ (75403) FLAGS (\Deleted)) + S: * 4 FETCH (UID 408 MODSEQ (29738) FLAGS ($NoJunk + $AutoJunk $MDNSent)) + S: s100 OK FETCH completed + + + + + + + + + +Melnikov, et al. Standards Track [Page 9] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + +3.3. EXPUNGE Command + + Arguments: none + + Responses: untagged responses: EXPUNGE or VANISHED + + Result: OK - expunge completed + NO - expunge failure: can't expunge (e.g., permission denied) + BAD - command unknown or arguments invalid + + This section updates the definition of the EXPUNGE command described + in Section 6.4.3 of [RFC3501]. + + The EXPUNGE command permanently removes all messages that have the + \Deleted flag set from the currently selected mailbox. Before + returning an OK to the client, those messages that are removed are + reported using a VANISHED response or EXPUNGE responses. + + If the server is capable of storing modification sequences for the + selected mailbox, it MUST increment the per-mailbox mod-sequence if + at least one message was permanently removed due to the execution of + the EXPUNGE command. For each permanently removed message, the + server MUST remember the incremented mod-sequence and corresponding + UID. If at least one message got expunged, the server MUST send the + updated per-mailbox modification sequence using the HIGHESTMODSEQ + response code (defined in [CONDSTORE]) in the tagged OK response. + + Example: C: A202 EXPUNGE + S: * 3 EXPUNGE + S: * 3 EXPUNGE + S: * 5 EXPUNGE + S: * 8 EXPUNGE + S: A202 OK [HIGHESTMODSEQ 20010715194045319] expunged + + Note: In this example, messages 3, 4, 7, and 11 had the \Deleted flag + set. The first "* 3 EXPUNGE" reports message # 3 as expunged. The + second "* 3 EXPUNGE" reports message # 4 as expunged (the message + number got decremented due to the previous EXPUNGE response). See + the description of the EXPUNGE response in [RFC3501] for further + explanation. + + Note that if the server chooses to always send VANISHED responses + instead of EXPUNGE responses, the previous example might look like + this: + + Example: C: B202 EXPUNGE + S: * VANISHED 405,407,410,425 + S: B202 OK [HIGHESTMODSEQ 20010715194045319] expunged + + + +Melnikov, et al. Standards Track [Page 10] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + Here messages with message numbers 3, 4, 7, and 11 have respective + UIDs 405, 407, 410, and 425. + +3.4. CLOSE Command + + Arguments: none + + Responses: no specific responses for this command + + Result: OK - close completed, now in authenticated state + BAD - command unknown or arguments invalid + + This section updates the definition of the CLOSE command described in + Section 6.4.2 of [RFC3501]. + + The CLOSE command permanently removes all messages that have the + \Deleted flag set from the currently selected mailbox, and returns to + the authenticated state from the selected state. No untagged EXPUNGE + (or VANISHED) responses are sent. + + If the server is capable of storing modification sequences for the + selected mailbox, it MUST increment the per-mailbox mod-sequence if + at least one message was permanently removed due to the execution of + the CLOSE command. For each permanently removed message, the server + MUST remember the incremented mod-sequence and corresponding UID. If + at least one message got expunged, the server MUST send the updated + per-mailbox modification sequence using the HIGHESTMODSEQ response + code (defined in [CONDSTORE]) in the tagged OK response. + + Example: C: A202 CLOSE + S: A202 OK [HIGHESTMODSEQ 20010715194045319] done + +3.5. UID EXPUNGE Command + + Arguments: message set + + Responses: untagged responses: EXPUNGE or VANISHED + + Result: OK - expunge completed + NO - expunge failure: can't expunge (e.g., permission denied) + BAD - command unknown or arguments invalid + + This section updates the definition of the UID EXPUNGE command + described in Section 2.1 of [UIDPLUS]. Servers that implement both + [UIDPLUS] and QRESYNC extensions must implement UID EXPUNGE as + described in this section. + + + + + +Melnikov, et al. Standards Track [Page 11] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + The UID EXPUNGE command permanently removes from the currently + selected mailbox all messages that both have the \Deleted flag set + and have a UID that is included in the specified message set. If a + message either does not have the \Deleted flag set or has a UID that + is not included in the specified message set, it is not affected. + + This command is particularly useful for disconnected mode clients. + By using UID EXPUNGE instead of EXPUNGE when resynchronizing with the + server, the client can avoid inadvertently removing any messages that + have been marked as \Deleted by other clients between the time that + the client was last connected and the time the client resynchronizes. + + Before returning an OK to the client, those messages that are removed + are reported using a VANISHED response or EXPUNGE responses. + + If the server is capable of storing modification sequences for the + selected mailbox, it MUST increment the per-mailbox mod-sequence if + at least one message was permanently removed due to the execution of + the UID EXPUNGE command. For each permanently removed message, the + server MUST remember the incremented mod-sequence and corresponding + UID. If at least one message got expunged, the server MUST send the + updated per-mailbox modification sequence using the HIGHESTMODSEQ + response code (defined in [CONDSTORE]) in the tagged OK response. + + Example: C: . UID EXPUNGE 3000:3002 + S: * 3 EXPUNGE + S: * 3 EXPUNGE + S: * 3 EXPUNGE + S: . OK [HIGHESTMODSEQ 20010715194045319] Ok + + Note: In this example, at least messages with message numbers 3, 4, + and 5 (UIDs 3000 to 3002) had the \Deleted flag set. The first "* 3 + EXPUNGE" reports message # 3 as expunged. The second "* 3 EXPUNGE" + reports message # 4 as expunged (the message number got decremented + due to the previous EXPUNGE response). See the description of the + EXPUNGE response in [RFC3501] for further explanation. + +3.6. VANISHED Response + + Contents: an optional EARLIER tag + + list of UIDs + + The VANISHED response reports that the specified UIDs have been + permanently removed from the mailbox. This response is similar to + the EXPUNGE response [RFC3501]; however, it can return information + about multiple messages, and it returns UIDs instead of message + + + + +Melnikov, et al. Standards Track [Page 12] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + numbers. The first benefit saves bandwidth, while the second is more + convenient for clients that only use UIDs to access the IMAP server. + + The VANISHED response has the same restrictions on when it can be + sent as does the EXPUNGE response (see below). + + The VANISHED response has two forms. The first form contains the + EARLIER tag, which signifies that the response was caused by a UID + FETCH (VANISHED) or a SELECT/EXAMINE (QRESYNC) command. This + response is sent if the UID set parameter to the UID FETCH (VANISHED) + command includes UIDs of messages that are no longer in the mailbox. + When the client sees a VANISHED EARLIER response, it MUST NOT + decrement message sequence numbers for each successive message in the + mailbox. + + The second form doesn't contain the EARLIER tag and is described + below. Once a client has issued "ENABLE QRESYNC", the server SHOULD + use the VANISHED response without the EARLIER tag instead of the + EXPUNGE response. The server SHOULD continue using VANISHED in lieu + of EXPUNGE for the duration of the connection. In particular, this + affects the EXPUNGE [RFC3501] and UID EXPUNGE [UIDPLUS] commands, as + well as messages expunged in other connections. Such a VANISHED + response MUST NOT contain the EARLIER tag. + + A VANISHED response sent because of an EXPUNGE or UID EXPUNGE command + or because messages were expunged in other connections (i.e., the + VANISHED response without the EARLIER tag) also decrements the number + of messages in the mailbox; it is not necessary for the server to + send an EXISTS response with the new value. It also decrements + message sequence numbers for each successive message in the mailbox + (see the example at the end of this section). Note that a VANISHED + response caused by EXPUNGE, UID EXPUNGE, or messages expunged in + other connections SHOULD only contain UIDs for messages expunged + since the last VANISHED/EXPUNGE response sent for the currently + opened mailbox or since the mailbox was opened. That is, servers + SHOULD NOT send UIDs for previously expunged messages, unless + explicitly requested to do so by the UID FETCH (VANISHED) command. + + Note that client implementors must take care to properly decrement + the number of messages in the mailbox even if a server violates this + last SHOULD or repeats the same UID multiple times in the returned + UID set. In general, this means that a client using this extension + should either avoid using message numbers entirely, or have a + complete mapping of UIDs to message sequence numbers for the selected + mailbox. + + + + + + +Melnikov, et al. Standards Track [Page 13] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + Because clients handle the two different forms of the VANISHED + response differently, servers MUST NOT report UIDs resulting from a + UID FETCH (VANISHED) or a SELECT/EXAMINE (QRESYNC) in the same + VANISHED response as UIDs of messages expunged now (i.e., messages + expunged in other connections). Instead, the server MUST send + separate VANISHED responses: one with the EARLIER tag and one + without. + + A VANISHED response MUST NOT be sent when no command is in progress, + nor while responding to a FETCH, STORE, or SEARCH command. This rule + is necessary to prevent a loss of synchronization of message sequence + numbers between client and server. A command is not "in progress" + until the complete command has been received; in particular, a + command is not "in progress" during the negotiation of command + continuation. + + Note: UID FETCH, UID STORE, and UID SEARCH are different commands + from FETCH, STORE, and SEARCH. A VANISHED response MAY be sent + during a UID command. However, the VANISHED response MUST NOT be + sent during a UID SEARCH command that contains message numbers in the + search criteria. + + The update from the VANISHED response MUST be recorded by the client. + + Example: Let's assume that there is the following mapping between + message numbers and UIDs in the currently selected mailbox (here "X" + marks messages with the \Deleted flag set, and "x" represents UIDs + which are not relevant for the example): + + Message numbers: 1 2 3 4 5 6 7 8 9 10 11 + UIDs: x 504 505 507 508 x 510 x x x 625 + \Deleted messages: X X X X + + In the presence of the extension defined in this document: + + C: A202 EXPUNGE + S: * VANISHED 505,507,510,625 + S: A202 OK EXPUNGE completed + + Without the QRESYNC extension, the same example might look like: + + C: A202 EXPUNGE + S: * 3 EXPUNGE + S: * 3 EXPUNGE + S: * 5 EXPUNGE + S: * 8 EXPUNGE + S: A202 OK EXPUNGE completed + + + + +Melnikov, et al. Standards Track [Page 14] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + (Continuing previous example) If subsequently messages with UIDs 504 + and 508 got marked as \Deleted: + + C: A210 EXPUNGE + S: * VANISHED 504,508 + S: A210 OK EXPUNGE completed + + i.e., the last VANISHED response only contains UIDs of messages + expunged since the previous VANISHED response. + +3.7. CLOSED Response Code + + The CLOSED response code has no parameters. A server implementing + the extension defined in this document MUST return the CLOSED + response code when the currently selected mailbox is closed + implicitly using the SELECT/EXAMINE command on another mailbox. The + CLOSED response code serves as a boundary between responses for the + previously opened mailbox (which was closed) and the newly selected + mailbox: all responses before the CLOSED response code relate to the + mailbox that was closed, and all subsequent responses relate to the + newly opened mailbox. + + There is no need to return the CLOSED response code on completion of + the CLOSE or the UNSELECT [UNSELECT] command (or similar) whose + purpose is to close the currently selected mailbox without opening a + new one. + +4. Server Implementation Considerations + + This section describes a minimalist implementation, a moderate + implementation, and an example of a full implementation. + +4.1. Server Implementations That Don't Store Extra State + + Strictly speaking, a server implementation that doesn't remember mod- + sequences associated with expunged messages can be considered + compliant with this specification. Such implementations return all + expunged messages specified in the UID set of the UID FETCH + (VANISHED) command every time, without paying attention to the + specified CHANGEDSINCE mod-sequence. Such implementations are + discouraged, as they can end up returning VANISHED responses that are + bigger than the result of a UID SEARCH command for the same UID set. + + Clients that use the message sequence match data can reduce the scope + of this VANISHED response substantially in the typical case where + expunges have not happened, or happen only toward the end of the + mailbox. + + + + +Melnikov, et al. Standards Track [Page 15] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + +4.2. Server Implementations Storing Minimal State + + A server that stores the HIGHESTMODSEQ value at the time of the last + EXPUNGE can omit the VANISHED response when a client provides a + MODSEQ value that is equal to, or higher than, the current value of + this datum, that is, when there have been no EXPUNGEs. + + A client providing message sequence match data can reduce the scope + as above. In the case where there have been no expunges, the server + can ignore this data. + +4.3. Additional State Required on the Server + + When compared to the [CONDSTORE] extension, this extension requires + servers to store additional state associated with expunged messages. + Note that implementations are not required to store this state in + persistent storage; however, use of persistent storage is advisable. + + One possible way to correctly implement the extension described in + this document is to store a queue of <UID set, mod-sequence> pairs. + <UID set> can be represented as a sequence of <min UID, max UID> + pairs. + + When messages are expunged, one or more entries are added to the + queue tail. + + When the server receives a request to return messages expunged since + a given mod-sequence, it will search the queue from the tail (i.e., + going from the highest expunged mod-sequence to the lowest) until it + sees the first record with a mod-sequence less than or equal to the + given mod-sequence or it reaches the head of the queue. + + Note that indefinitely storing information about expunged messages + can cause storage and related problems for an implementation. In the + worst case, this could result in almost 64Gb of storage for each IMAP + mailbox. For example, consider an implementation that stores <min + UID, max UID, mod-sequence> triples for each range of messages + expunged at the same time. Each triple requires 16 octets: 4 octets + for each of the two UIDs, and 8 octets for the mod-sequence. Assume + that there is a mailbox containing a single message with a UID of + 2**32-1 (the maximum possible UID value), where messages had + previously existed with UIDs starting at 1, and have been expunged + one at a time. For this mailbox alone, storage is required for the + triples <1, 1, modseq1>, <2, 2, modseq2>, ..., <2**32-2, 2**32-2, + modseq4294967294>. + + + + + + +Melnikov, et al. Standards Track [Page 16] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + Hence, implementations are encouraged to adopt strategies to protect + against such storage problems, such as limiting the size of the queue + used to store mod-sequences for expunged messages and "expiring" + older records when this limit is reached. When the selected + implementation-specific queue limit is reached, the oldest record(s) + are deleted from the queue (note that such records are located at the + queue head). For all such "expired" records, the server needs to + store a single mod-sequence, which is the highest mod-sequence for + all "expired" expunged messages. + + Note that if the client provides the message sequence match data, + this can heavily reduce the data cost of sending a complete set of + missing UIDs; thus, reducing the problems for clients if a server is + unable to persist much of this queue. If the queue contains data + back to the requested mod-sequence, this data can be ignored. + + Also, note that if the UIDVALIDITY of the mailbox changes or if the + mailbox is deleted, then any state associated with expunged messages + doesn't need to be preserved and SHOULD be deleted. + +5. Updated Synchronization Sequence + + This section updates the description of optimized synchronization in + Section 6.1 of the [IMAP-DISC]. + + An advanced disconnected mail client should use the QRESYNC and + [CONDSTORE] extensions when they are supported by the server. The + client uses the value from the HIGHESTMODSEQ OK response code + received on mailbox opening to determine if it needs to + resynchronize. Once the synchronization is complete, it MUST cache + the received value (unless the mailbox UIDVALIDITY value has changed; + see below). The client MUST update its copy of the HIGHESTMODSEQ + value whenever the server sends a subsequent HIGHESTMODSEQ OK + response code. + + After completing a full synchronization, the client MUST also take + note of any unsolicited MODSEQ FETCH data items received from the + server. Whenever the client receives a tagged response to a command, + it calculates the highest value among all MODSEQ FETCH data items + received since the last tagged response. If this value is bigger + than the client's copy of the HIGHESTMODSEQ value, then the client + MUST use this value as its new HIGHESTMODSEQ value. + + Note: It is not safe to update the client's copy of the HIGHESTMODSEQ + value with a MODSEQ FETCH data item value as soon as it is received + because servers are not required to send MODSEQ FETCH data items in + increasing modseqence order. This can lead to the client missing + some changes in case of connectivity loss. + + + +Melnikov, et al. Standards Track [Page 17] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + When opening the mailbox for synchronization, the client uses the + QRESYNC parameter to the SELECT/EXAMINE command. The QRESYNC + parameter is followed by the UIDVALIDITY and mailbox HIGHESTMODSEQ + values, as known to the client. It can be optionally followed by the + set of UIDs, for example, if the client is only interested in partial + synchronization of the mailbox. The client may also transmit a list + containing its knowledge of message numbers. + + If the SELECT/EXAMINE command is successful, the client compares + UIDVALIDITY as described in step d)1) in Section 3 of the + [IMAP-DISC]. If the cached UIDVALIDITY value matches the one + returned by the server and the server also returns the HIGHESTMODSEQ + response code, then the server reports expunged messages and returns + flag changes for all messages specified by the client in the UID set + parameter (or for all messages in the mailbox, if the client omitted + the UID set parameter). At this point, the client is synchronized, + except for maybe the new messages. + + If upon a successful SELECT/EXAMINE (QRESYNC) command the client + receives a NOMODSEQ OK untagged response (instead of the + HIGHESTMODSEQ response code), it MUST remove the last known + HIGHESTMODSEQ value from its cache and follow the more general + instructions in Section 3 of the [IMAP-DISC]. + + At this point, the client is in sync with the server regarding old + messages. This client can now fetch information about new messages + (if requested by the user). + + Step d) ("Server-to-client synchronization") in Section 4 of the + [IMAP-DISC] in the presence of the QRESYNC & CONDSTORE extensions is + amended as follows: + + d) "Server-to-client synchronization" -- for each mailbox that + requires synchronization, do the following: + + 1a) Check the mailbox UIDVALIDITY (see Section 4.1 of the [IMAP-DISC] + for more details) after issuing SELECT/EXAMINE (QRESYNC) command. + + If the UIDVALIDITY value returned by the server differs, the + client MUST + + * empty the local cache of that mailbox; + + * "forget" the cached HIGHESTMODSEQ value for the mailbox; + + + + + + + +Melnikov, et al. Standards Track [Page 18] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + * remove any pending "actions" which refer to UIDs in that + mailbox. Note, this doesn't affect actions performed on + client generated fake UIDs (see Section 5 of the + [IMAP-DISC]); + + 2) Fetch the current "descriptors"; + + I) Discover new messages. + + 3) Fetch the bodies of any "interesting" messages that the client + doesn't already have. + + Example: The UIDVALIDITY value is the same, but the HIGHESTMODSEQ + value has changed on the server while the client was + offline: + + C: A142 SELECT INBOX (QRESYNC (3857529045 20010715194032001 1:198)) + S: * 172 EXISTS + S: * 1 RECENT + S: * OK [UNSEEN 12] Message 12 is first unseen + S: * OK [UIDVALIDITY 3857529045] UIDs valid + S: * OK [UIDNEXT 201] Predicted next UID + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited + S: * OK [HIGHESTMODSEQ 20010715194045007] + S: * VANISHED (EARLIER) 1:5,7:8,10:15 + S: * 2 FETCH (UID 6 MODSEQ (20010715205008000) + FLAGS (\Deleted)) + S: * 5 FETCH (UID 9 MODSEQ (20010715195517000) + FLAGS ($NoJunk $AutoJunk $MDNSent)) + ... + S: A142 OK [READ-WRITE] SELECT completed + +6. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [ABNF]. + + Non-terminals referenced but not defined below are as defined by + [RFC3501], [CONDSTORE], or [IMAPABNF]. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper or lower case characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + + + + + +Melnikov, et al. Standards Track [Page 19] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + + capability =/ "QRESYNC" + + select-param = "QRESYNC" SP "(" uidvalidity SP + mod-sequence-value [SP known-uids] + [SP seq-match-data] ")" + ;; conforms to the generic select-param + ;; syntax defined in [IMAPABNF] + + seq-match-data = "(" known-sequence-set SP known-uid-set ")" + + uidvalidity = nz-number + + known-uids = sequence-set + ;; sequence of UIDs, "*" is not allowed + + known-sequence-set = sequence-set + ;; set of message numbers corresponding to + ;; the UIDs in known-uid-set, in ascending order. + ;; * is not allowed. + + known-uid-set = sequence-set + ;; set of UIDs corresponding to the messages in + ;; known-sequence-set, in ascending order. + ;; * is not allowed. + + message-data =/ expunged-resp + + expunged-resp = "VANISHED" [SP "(EARLIER)"] SP known-uids + + rexpunges-fetch-mod = "VANISHED" + ;; VANISHED UID FETCH modifier conforms + ;; to the fetch-modifier syntax + ;; defined in [IMAPABNF]. It is only + ;; allowed in the UID FETCH command. + + resp-text-code =/ "CLOSED" + +7. Security Considerations + + As always, it is important to thoroughly test clients and servers + implementing this extension, as it changes how the server reports + expunged messages to the client. + + Security considerations relevant to [CONDSTORE] are relevant to this + extension. + + This document doesn't raise any new security concerns not already + raised by [CONDSTORE] or [RFC3501]. + + + +Melnikov, et al. Standards Track [Page 20] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + +8. IANA Considerations + + IMAP4 capabilities are registered by publishing a standards track or + IESG approved experimental RFC. The registry is currently located + at: + + http://www.iana.org/assignments/imap4-capabilities + + This document defines the QRESYNC IMAP capability. IANA has added + this capability to the registry. + +9. Acknowledgments + + Thanks to Steve Hole, Cyrus Daboo, and Michael Wener for encouraging + creation of this document. + + Valuable comments, both in agreement and in dissent, were received + from Timo Sirainen, Michael Wener, Randall Gellens, Arnt Gulbrandsen, + Chris Newman, Peter Coates, Mark Crispin, Elwyn Davies, Dan Karp, + Eric Rescorla, and Mike Zraly. + + This document takes substantial text from [RFC3501] by Mark Crispin. + +10. References + +10.1. Normative References + + [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", STD 68, RFC 5234, January 2008. + + [CONDSTORE] Melnikov, A. and S. Hole, "IMAP Extension for + Conditional STORE Operation or Quick Flag Changes + Resynchronization", RFC 4551, June 2006. + + [ENABLE] Gulbrandsen, A., Ed. and A. Melnikov, Ed., "The IMAP + ENABLE Extension", RFC 5161, March 2008. + + [IMAPABNF] Melnikov, A. and C. Daboo, "Collected Extensions to + IMAP4 ABNF", RFC 4466, April 2006. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [UIDPLUS] Crispin, M., "Internet Message Access Protocol (IMAP) - + UIDPLUS extension", RFC 4315, December 2005. + + + +Melnikov, et al. Standards Track [Page 21] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + +10.2. Informative References + + [IMAP-DISC] Melnikov, A., Ed., "Synchronization Operations For + Disconnected Imap4 Clients", RFC 4549, June 2006. + + [UNSELECT] Melnikov, A., "Internet Message Access Protocol (IMAP) + UNSELECT command", RFC 3691, February 2004. + +Authors' Addresses + + Alexey Melnikov + Isode Ltd + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: Alexey.Melnikov@isode.com + + + Dave Cridland + Isode Ltd + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: dave.cridland@isode.com + + + Corby Wilson + Nokia + 5 Wayside Rd. + Burlington, MA 01803 + USA + + EMail: corby@computer.org + + + + + + + + + + + + + + +Melnikov, et al. Standards Track [Page 22] + +RFC 5162 IMAP Quick Mailbox Resync March 2008 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2008). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Melnikov, et al. Standards Track [Page 23] + diff --git a/imap/docs/rfc/rfc5234.txt b/imap/docs/rfc/rfc5234.txt new file mode 100644 index 00000000..42bb44ca --- /dev/null +++ b/imap/docs/rfc/rfc5234.txt @@ -0,0 +1,899 @@ + + + + + + +Network Working Group D. Crocker, Ed. +Request for Comments: 5234 Brandenburg InternetWorking +STD: 68 P. Overell +Obsoletes: 4234 THUS plc. +Category: Standards Track January 2008 + + + Augmented BNF for Syntax Specifications: ABNF + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + Internet technical specifications often need to define a formal + syntax. Over the years, a modified version of Backus-Naur Form + (BNF), called Augmented BNF (ABNF), has been popular among many + Internet specifications. The current specification documents ABNF. + It balances compactness and simplicity with reasonable + representational power. The differences between standard BNF and + ABNF involve naming rules, repetition, alternatives, order- + independence, and value ranges. This specification also supplies + additional rule definitions and encoding for a core lexical analyzer + of the type common to several Internet specifications. + + + + + + + + + + + + + + + + + + + + + + +Crocker & Overell Standards Track [Page 1] + +RFC 5234 ABNF January 2008 + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 + 2. Rule Definition . . . . . . . . . . . . . . . . . . . . . . . 3 + 2.1. Rule Naming . . . . . . . . . . . . . . . . . . . . . . . 3 + 2.2. Rule Form . . . . . . . . . . . . . . . . . . . . . . . . 4 + 2.3. Terminal Values . . . . . . . . . . . . . . . . . . . . . 4 + 2.4. External Encodings . . . . . . . . . . . . . . . . . . . . 6 + 3. Operators . . . . . . . . . . . . . . . . . . . . . . . . . . 6 + 3.1. Concatenation: Rule1 Rule2 . . . . . . . . . . . . . . . 6 + 3.2. Alternatives: Rule1 / Rule2 . . . . . . . . . . . . . . . 7 + 3.3. Incremental Alternatives: Rule1 =/ Rule2 . . . . . . . . . 7 + 3.4. Value Range Alternatives: %c##-## . . . . . . . . . . . . 8 + 3.5. Sequence Group: (Rule1 Rule2) . . . . . . . . . . . . . . 8 + 3.6. Variable Repetition: *Rule . . . . . . . . . . . . . . . 9 + 3.7. Specific Repetition: nRule . . . . . . . . . . . . . . . 9 + 3.8. Optional Sequence: [RULE] . . . . . . . . . . . . . . . . 9 + 3.9. Comment: ; Comment . . . . . . . . . . . . . . . . . . . 9 + 3.10. Operator Precedence . . . . . . . . . . . . . . . . . . . 10 + 4. ABNF Definition of ABNF . . . . . . . . . . . . . . . . . . . 10 + 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 + 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 + 6.1. Normative References . . . . . . . . . . . . . . . . . . . 12 + 6.2. Informative References . . . . . . . . . . . . . . . . . . 12 + Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 13 + Appendix B. Core ABNF of ABNF . . . . . . . . . . . . . . . . . . 13 + B.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . . . 13 + B.2. Common Encoding . . . . . . . . . . . . . . . . . . . . . 15 + + + + + + + + + + + + + + + + + + + + + + + +Crocker & Overell Standards Track [Page 2] + +RFC 5234 ABNF January 2008 + + +1. Introduction + + Internet technical specifications often need to define a formal + syntax and are free to employ whatever notation their authors deem + useful. Over the years, a modified version of Backus-Naur Form + (BNF), called Augmented BNF (ABNF), has been popular among many + Internet specifications. It balances compactness and simplicity with + reasonable representational power. In the early days of the Arpanet, + each specification contained its own definition of ABNF. This + included the email specifications, [RFC733] and then [RFC822], which + came to be the common citations for defining ABNF. The current + document separates those definitions to permit selective reference. + Predictably, it also provides some modifications and enhancements. + + The differences between standard BNF and ABNF involve naming rules, + repetition, alternatives, order-independence, and value ranges. + Appendix B supplies rule definitions and encoding for a core lexical + analyzer of the type common to several Internet specifications. It + is provided as a convenience and is otherwise separate from the meta + language defined in the body of this document, and separate from its + formal status. + +2. Rule Definition + +2.1. Rule Naming + + The name of a rule is simply the name itself, that is, a sequence of + characters, beginning with an alphabetic character, and followed by a + combination of alphabetics, digits, and hyphens (dashes). + + NOTE: + + Rule names are case insensitive. + + The names <rulename>, <Rulename>, <RULENAME>, and <rUlENamE> all + refer to the same rule. + + Unlike original BNF, angle brackets ("<", ">") are not required. + However, angle brackets may be used around a rule name whenever their + presence facilitates in discerning the use of a rule name. This is + typically restricted to rule name references in free-form prose, or + to distinguish partial rules that combine into a string not separated + by white space, such as shown in the discussion about repetition, + below. + + + + + + + +Crocker & Overell Standards Track [Page 3] + +RFC 5234 ABNF January 2008 + + +2.2. Rule Form + + A rule is defined by the following sequence: + + name = elements crlf + + where <name> is the name of the rule, <elements> is one or more rule + names or terminal specifications, and <crlf> is the end-of-line + indicator (carriage return followed by line feed). The equal sign + separates the name from the definition of the rule. The elements + form a sequence of one or more rule names and/or value definitions, + combined according to the various operators defined in this document, + such as alternative and repetition. + + For visual ease, rule definitions are left aligned. When a rule + requires multiple lines, the continuation lines are indented. The + left alignment and indentation are relative to the first lines of the + ABNF rules and need not match the left margin of the document. + +2.3. Terminal Values + + Rules resolve into a string of terminal values, sometimes called + characters. In ABNF, a character is merely a non-negative integer. + In certain contexts, a specific mapping (encoding) of values into a + character set (such as ASCII) will be specified. + + Terminals are specified by one or more numeric characters, with the + base interpretation of those characters indicated explicitly. The + following bases are currently defined: + + b = binary + + d = decimal + + x = hexadecimal + + Hence: + + CR = %d13 + + CR = %x0D + + respectively specify the decimal and hexadecimal representation of + [US-ASCII] for carriage return. + + + + + + + +Crocker & Overell Standards Track [Page 4] + +RFC 5234 ABNF January 2008 + + + A concatenated string of such values is specified compactly, using a + period (".") to indicate a separation of characters within that + value. Hence: + + CRLF = %d13.10 + + ABNF permits the specification of literal text strings directly, + enclosed in quotation marks. Hence: + + command = "command string" + + Literal text strings are interpreted as a concatenated set of + printable characters. + + NOTE: + + ABNF strings are case insensitive and the character set for these + strings is US-ASCII. + + Hence: + + rulename = "abc" + + and: + + rulename = "aBc" + + will match "abc", "Abc", "aBc", "abC", "ABc", "aBC", "AbC", and + "ABC". + + To specify a rule that is case sensitive, specify the characters + individually. + + For example: + + rulename = %d97 %d98 %d99 + + or + + rulename = %d97.98.99 + + will match only the string that comprises only the lowercase + characters, abc. + + + + + + + + +Crocker & Overell Standards Track [Page 5] + +RFC 5234 ABNF January 2008 + + +2.4. External Encodings + + External representations of terminal value characters will vary + according to constraints in the storage or transmission environment. + Hence, the same ABNF-based grammar may have multiple external + encodings, such as one for a 7-bit US-ASCII environment, another for + a binary octet environment, and still a different one when 16-bit + Unicode is used. Encoding details are beyond the scope of ABNF, + although Appendix B provides definitions for a 7-bit US-ASCII + environment as has been common to much of the Internet. + + By separating external encoding from the syntax, it is intended that + alternate encoding environments can be used for the same syntax. + +3. Operators + +3.1. Concatenation: Rule1 Rule2 + + A rule can define a simple, ordered string of values (i.e., a + concatenation of contiguous characters) by listing a sequence of rule + names. For example: + + foo = %x61 ; a + + bar = %x62 ; b + + mumble = foo bar foo + + So that the rule <mumble> matches the lowercase string "aba". + + Linear white space: Concatenation is at the core of the ABNF parsing + model. A string of contiguous characters (values) is parsed + according to the rules defined in ABNF. For Internet specifications, + there is some history of permitting linear white space (space and + horizontal tab) to be freely and implicitly interspersed around major + constructs, such as delimiting special characters or atomic strings. + + NOTE: + + This specification for ABNF does not provide for implicit + specification of linear white space. + + Any grammar that wishes to permit linear white space around + delimiters or string segments must specify it explicitly. It is + often useful to provide for such white space in "core" rules that are + then used variously among higher-level rules. The "core" rules might + be formed into a lexical analyzer or simply be part of the main + ruleset. + + + +Crocker & Overell Standards Track [Page 6] + +RFC 5234 ABNF January 2008 + + +3.2. Alternatives: Rule1 / Rule2 + + Elements separated by a forward slash ("/") are alternatives. + Therefore, + + foo / bar + + will accept <foo> or <bar>. + + NOTE: + + A quoted string containing alphabetic characters is a special form + for specifying alternative characters and is interpreted as a non- + terminal representing the set of combinatorial strings with the + contained characters, in the specified order but with any mixture + of upper- and lowercase. + +3.3. Incremental Alternatives: Rule1 =/ Rule2 + + It is sometimes convenient to specify a list of alternatives in + fragments. That is, an initial rule may match one or more + alternatives, with later rule definitions adding to the set of + alternatives. This is particularly useful for otherwise independent + specifications that derive from the same parent ruleset, such as + often occurs with parameter lists. ABNF permits this incremental + definition through the construct: + + oldrule =/ additional-alternatives + + So that the ruleset + + ruleset = alt1 / alt2 + + ruleset =/ alt3 + + ruleset =/ alt4 / alt5 + + is the same as specifying + + ruleset = alt1 / alt2 / alt3 / alt4 / alt5 + + + + + + + + + + + +Crocker & Overell Standards Track [Page 7] + +RFC 5234 ABNF January 2008 + + +3.4. Value Range Alternatives: %c##-## + + A range of alternative numeric values can be specified compactly, + using a dash ("-") to indicate the range of alternative values. + Hence: + + DIGIT = %x30-39 + + is equivalent to: + + DIGIT = "0" / "1" / "2" / "3" / "4" / "5" / "6" / + + "7" / "8" / "9" + + Concatenated numeric values and numeric value ranges cannot be + specified in the same string. A numeric value may use the dotted + notation for concatenation or it may use the dash notation to specify + one value range. Hence, to specify one printable character between + end-of-line sequences, the specification could be: + + char-line = %x0D.0A %x20-7E %x0D.0A + +3.5. Sequence Group: (Rule1 Rule2) + + Elements enclosed in parentheses are treated as a single element, + whose contents are strictly ordered. Thus, + + elem (foo / bar) blat + + matches (elem foo blat) or (elem bar blat), and + + elem foo / bar blat + + matches (elem foo) or (bar blat). + + NOTE: + + It is strongly advised that grouping notation be used, rather than + relying on the proper reading of "bare" alternations, when + alternatives consist of multiple rule names or literals. + + Hence, it is recommended that the following form be used: + + (elem foo) / (bar blat) + + It will avoid misinterpretation by casual readers. + + + + + +Crocker & Overell Standards Track [Page 8] + +RFC 5234 ABNF January 2008 + + + The sequence group notation is also used within free text to set off + an element sequence from the prose. + +3.6. Variable Repetition: *Rule + + The operator "*" preceding an element indicates repetition. The full + form is: + + <a>*<b>element + + where <a> and <b> are optional decimal values, indicating at least + <a> and at most <b> occurrences of the element. + + Default values are 0 and infinity so that *<element> allows any + number, including zero; 1*<element> requires at least one; + 3*3<element> allows exactly 3; and 1*2<element> allows one or two. + +3.7. Specific Repetition: nRule + + A rule of the form: + + <n>element + + is equivalent to + + <n>*<n>element + + That is, exactly <n> occurrences of <element>. Thus, 2DIGIT is a + 2-digit number, and 3ALPHA is a string of three alphabetic + characters. + +3.8. Optional Sequence: [RULE] + + Square brackets enclose an optional element sequence: + + [foo bar] + + is equivalent to + + *1(foo bar). + +3.9. Comment: ; Comment + + A semicolon starts a comment that continues to the end of line. This + is a simple way of including useful notes in parallel with the + specifications. + + + + + +Crocker & Overell Standards Track [Page 9] + +RFC 5234 ABNF January 2008 + + +3.10. Operator Precedence + + The various mechanisms described above have the following precedence, + from highest (binding tightest) at the top, to lowest (loosest) at + the bottom: + + Rule name, prose-val, Terminal value + + Comment + + Value range + + Repetition + + Grouping, Optional + + Concatenation + + Alternative + + Use of the alternative operator, freely mixed with concatenations, + can be confusing. + + Again, it is recommended that the grouping operator be used to + make explicit concatenation groups. + +4. ABNF Definition of ABNF + + NOTES: + + 1. This syntax requires a formatting of rules that is relatively + strict. Hence, the version of a ruleset included in a + specification might need preprocessing to ensure that it can + be interpreted by an ABNF parser. + + 2. This syntax uses the rules provided in Appendix B. + + + rulelist = 1*( rule / (*c-wsp c-nl) ) + + rule = rulename defined-as elements c-nl + ; continues if next line starts + ; with white space + + rulename = ALPHA *(ALPHA / DIGIT / "-") + + + + + + +Crocker & Overell Standards Track [Page 10] + +RFC 5234 ABNF January 2008 + + + defined-as = *c-wsp ("=" / "=/") *c-wsp + ; basic rules definition and + ; incremental alternatives + + elements = alternation *c-wsp + + c-wsp = WSP / (c-nl WSP) + + c-nl = comment / CRLF + ; comment or newline + + comment = ";" *(WSP / VCHAR) CRLF + + alternation = concatenation + *(*c-wsp "/" *c-wsp concatenation) + + concatenation = repetition *(1*c-wsp repetition) + + repetition = [repeat] element + + repeat = 1*DIGIT / (*DIGIT "*" *DIGIT) + + element = rulename / group / option / + char-val / num-val / prose-val + + group = "(" *c-wsp alternation *c-wsp ")" + + option = "[" *c-wsp alternation *c-wsp "]" + + char-val = DQUOTE *(%x20-21 / %x23-7E) DQUOTE + ; quoted string of SP and VCHAR + ; without DQUOTE + + num-val = "%" (bin-val / dec-val / hex-val) + + bin-val = "b" 1*BIT + [ 1*("." 1*BIT) / ("-" 1*BIT) ] + ; series of concatenated bit values + ; or single ONEOF range + + dec-val = "d" 1*DIGIT + [ 1*("." 1*DIGIT) / ("-" 1*DIGIT) ] + + hex-val = "x" 1*HEXDIG + [ 1*("." 1*HEXDIG) / ("-" 1*HEXDIG) ] + + + + + + +Crocker & Overell Standards Track [Page 11] + +RFC 5234 ABNF January 2008 + + + prose-val = "<" *(%x20-3D / %x3F-7E) ">" + ; bracketed string of SP and VCHAR + ; without angles + ; prose description, to be used as + ; last resort + +5. Security Considerations + + Security is truly believed to be irrelevant to this document. + +6. References + +6.1. Normative References + + [US-ASCII] American National Standards Institute, "Coded Character + Set -- 7-bit American Standard Code for Information + Interchange", ANSI X3.4, 1986. + +6.2. Informative References + + [RFC733] Crocker, D., Vittal, J., Pogran, K., and D. Henderson, + "Standard for the format of ARPA network text messages", + RFC 733, November 1977. + + [RFC822] Crocker, D., "Standard for the format of ARPA Internet + text messages", STD 11, RFC 822, August 1982. + + + + + + + + + + + + + + + + + + + + + + + + + +Crocker & Overell Standards Track [Page 12] + +RFC 5234 ABNF January 2008 + + +Appendix A. Acknowledgements + + The syntax for ABNF was originally specified in RFC 733. Ken L. + Harrenstien, of SRI International, was responsible for re-coding the + BNF into an Augmented BNF that makes the representation smaller and + easier to understand. + + This recent project began as a simple effort to cull out the portion + of RFC 822 that has been repeatedly cited by non-email specification + writers, namely the description of Augmented BNF. Rather than simply + and blindly converting the existing text into a separate document, + the working group chose to give careful consideration to the + deficiencies, as well as benefits, of the existing specification and + related specifications made available over the last 15 years, and + therefore to pursue enhancement. This turned the project into + something rather more ambitious than was first intended. + Interestingly, the result is not massively different from that + original, although decisions, such as removing the list notation, + came as a surprise. + + This "separated" version of the specification was part of the DRUMS + working group, with significant contributions from Jerome Abela, + Harald Alvestrand, Robert Elz, Roger Fajman, Aviva Garrett, Tom + Harsch, Dan Kohn, Bill McQuillan, Keith Moore, Chris Newman, Pete + Resnick, and Henning Schulzrinne. + + Julian Reschke warrants a special thanks for converting the Draft + Standard version to XML source form. + +Appendix B. Core ABNF of ABNF + + This appendix contains some basic rules that are in common use. + Basic rules are in uppercase. Note that these rules are only valid + for ABNF encoded in 7-bit ASCII or in characters sets that are a + superset of 7-bit ASCII. + +B.1. Core Rules + + Certain basic rules are in uppercase, such as SP, HTAB, CRLF, DIGIT, + ALPHA, etc. + + ALPHA = %x41-5A / %x61-7A ; A-Z / a-z + + BIT = "0" / "1" + + CHAR = %x01-7F + ; any 7-bit US-ASCII character, + ; excluding NUL + + + +Crocker & Overell Standards Track [Page 13] + +RFC 5234 ABNF January 2008 + + + CR = %x0D + ; carriage return + + CRLF = CR LF + ; Internet standard newline + + CTL = %x00-1F / %x7F + ; controls + + DIGIT = %x30-39 + ; 0-9 + + DQUOTE = %x22 + ; " (Double Quote) + + HEXDIG = DIGIT / "A" / "B" / "C" / "D" / "E" / "F" + + HTAB = %x09 + ; horizontal tab + + LF = %x0A + ; linefeed + + LWSP = *(WSP / CRLF WSP) + ; Use of this linear-white-space rule + ; permits lines containing only white + ; space that are no longer legal in + ; mail headers and have caused + ; interoperability problems in other + ; contexts. + ; Do not use when defining mail + ; headers and use with caution in + ; other contexts. + + OCTET = %x00-FF + ; 8 bits of data + + SP = %x20 + + VCHAR = %x21-7E + ; visible (printing) characters + + WSP = SP / HTAB + ; white space + + + + + + + +Crocker & Overell Standards Track [Page 14] + +RFC 5234 ABNF January 2008 + + +B.2. Common Encoding + + Externally, data are represented as "network virtual ASCII" (namely, + 7-bit US-ASCII in an 8-bit field), with the high (8th) bit set to + zero. A string of values is in "network byte order", in which the + higher-valued bytes are represented on the left-hand side and are + sent over the network first. + +Authors' Addresses + + Dave Crocker (editor) + Brandenburg InternetWorking + 675 Spruce Dr. + Sunnyvale, CA 94086 + US + + Phone: +1.408.246.8253 + EMail: dcrocker@bbiw.net + + + Paul Overell + THUS plc. + 1/2 Berkeley Square, + 99 Berkeley Street + Glasgow G3 7HR + UK + + EMail: paul.overell@thus.net + + + + + + + + + + + + + + + + + + + + + + + +Crocker & Overell Standards Track [Page 15] + +RFC 5234 ABNF January 2008 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2008). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Crocker & Overell Standards Track [Page 16] + diff --git a/imap/docs/rfc/rfc5255.txt b/imap/docs/rfc/rfc5255.txt new file mode 100644 index 00000000..df76402c --- /dev/null +++ b/imap/docs/rfc/rfc5255.txt @@ -0,0 +1,1123 @@ + + + + + + +Network Working Group C. Newman +Request for Comments: 5255 Sun Microsystems +Category: Standards Track A. Gulbrandsen + Oryx Mail Systems GmhH + A. Melnikov + Isode Limited + June 2008 + + + Internet Message Access Protocol Internationalization + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + Internet Message Access Protocol (IMAP) version 4rev1 has basic + support for non-ASCII characters in mailbox names and search + substrings. It also supports non-ASCII message headers and content + encoded as specified by Multipurpose Internet Mail Extensions (MIME). + This specification defines a collection of IMAP extensions that + improve international support including language negotiation for + international error text, translations for namespace prefixes, and + comparator negotiation for search, sort, and thread. + + + + + + + + + + + + + + + + + + + + + + +Newman, et al. Standards Track [Page 1] + +RFC 5255 IMAP Internationalization June 2008 + + +Table of Contents + + 1. Introduction ....................................................3 + 2. Conventions Used in This Document ...............................3 + 3. LANGUAGE Extension ..............................................3 + 3.1. LANGUAGE Extension Requirements ............................4 + 3.2. LANGUAGE Command ...........................................4 + 3.3. LANGUAGE Response ..........................................6 + 3.4. TRANSLATION Extension to the NAMESPACE Response ............7 + 3.5. Formal Syntax ..............................................8 + 4. I18NLEVEL=1 and I18NLEVEL=2 Extensions ..........................9 + 4.1. Introduction and Overview ..................................9 + 4.2. Requirements Common to Both I18NLEVEL=1 and I18NLEVEL=2 ....9 + 4.3. I18NLEVEL=1 Extension Requirements ........................10 + 4.4. I18NLEVEL=2 Extension Requirements ........................10 + 4.5. Compatibility Notes .......................................11 + 4.6. Comparators and Character Encodings .......................11 + 4.7. COMPARATOR Command ........................................13 + 4.8. COMPARATOR Response .......................................14 + 4.9. BADCOMPARATOR Response Code ...............................14 + 4.10. Formal Syntax ............................................14 + 5. Other IMAP Internationalization Issues .........................15 + 5.1. Unicode Userids and Passwords .............................15 + 5.2. UTF-8 Mailbox Names .......................................15 + 5.3. UTF-8 Domains, Addresses, and Mail Headers ................15 + 6. IANA Considerations ............................................16 + 7. Security Considerations ........................................16 + 8. Acknowledgements ...............................................16 + 9. Relevant Sources of Documents for Internationalized IMAP + Implementations ................................................17 + 10. Normative References ..........................................17 + 11. Informative References ........................................18 + + + + + + + + + + + + + + + + + + + +Newman, et al. Standards Track [Page 2] + +RFC 5255 IMAP Internationalization June 2008 + + +1. Introduction + + This specification defines two IMAP4rev1 [RFC3501] extensions to + enhance international support. These extensions can be advertised + and implemented separately. + + The LANGUAGE extension allows the client to request a suitable + language for protocol error messages and in combination with the + NAMESPACE extension [RFC2342] enables namespace translations. + + The I18NLEVEL=2 extension allows the client to request a suitable + collation that will modify the behavior of the base specification's + SEARCH command as well as the SORT and THREAD extensions [SORT]. + This leverages the collation registry [RFC4790]. The I18NLEVEL=1 + extension updates SEARCH/SORT/THREAD to use i;unicode-casemap + comparator, as defined in [UCM]. I18NLEVEL=1 is a simpler version of + I18NLEVEL=2 with no ability to select a different collation. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + + The formal syntax uses the Augmented Backus-Naur Form (ABNF) + [RFC5234] notation including the core rules defined in Appendix A. + + The UTF-8-related productions are defined in [RFC3629]. + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. If a single "C:" or "S:" label applies to + multiple lines, then the line breaks between those lines are for + editorial clarity only and are not part of the actual protocol + exchange. + +3. LANGUAGE Extension + + IMAP allows server responses to include human-readable text that in + many cases needs to be presented to the user. But that text is + limited to US-ASCII by the IMAP specification [RFC3501] in order to + preserve backwards compatibility with deployed IMAP implementations. + This section specifies a way for an IMAP client to negotiate which + language the server should use when sending human-readable text. + + + + + + + + +Newman, et al. Standards Track [Page 3] + +RFC 5255 IMAP Internationalization June 2008 + + + The LANGUAGE extension only provides a mechanism for altering fixed + server strings such as response text and NAMESPACE folder names. + Assigning localized language aliases to shared mailboxes would be + done with a separate mechanism such as the proposed METADATA + extension (see [METADATA]). + +3.1. LANGUAGE Extension Requirements + + IMAP servers that support this extension MUST list the keyword + LANGUAGE in their CAPABILITY response as well as in the greeting + CAPABILITY data. + + A server that advertises this extension MUST use the language + "i-default" as described in [RFC2277] as its default language until + another supported language is negotiated by the client. A server + MUST include "i-default" as one of its supported languages. IMAP + servers SHOULD NOT advertise the LANGUAGE extension if they discover + that they only support "i-default". + + Clients and servers that support this extension MUST also support the + NAMESPACE extension [RFC2342]. + + The LANGUAGE command is valid in all states. Clients SHOULD issue + LANGUAGE before authentication, since some servers send valuable user + information as part of authentication (e.g., "password is correct, + but expired"). If a security layer (such as SASL or TLS) is + subsequently negotiated by the client, it MUST re-issue the LANGUAGE + command in order to make sure that no previous active attack (if any) + on LANGUAGE negotiation has effect on subsequent error messages. + (See Section 7 for a more detailed explanation of the attack.) + +3.2. LANGUAGE Command + + Arguments: Optional language range arguments. + + Response: A possible LANGUAGE response (see Section 3.3). + A possible NAMESPACE response (see Section 3.4). + + Result: OK - Command completed + NO - Could not complete command + BAD - Arguments invalid + + The LANGUAGE command requests that human-readable text emitted by the + server be localized to a language matching one of the language range + argument as described by Section 2 of [RFC4647]. + + + + + + +Newman, et al. Standards Track [Page 4] + +RFC 5255 IMAP Internationalization June 2008 + + + If the command succeeds, the server will return human-readable + responses in the first supported language specified. These responses + will be in UTF-8 [RFC3629]. The server MUST send a LANGUAGE response + specifying the language used, and the change takes effect immediately + after the LANGUAGE response. + + If the command fails, the server continues to return human-readable + responses in the language it was previously using. + + The special "default" language range argument indicates a request to + use a language designated as preferred by the server administrator. + The preferred language MAY vary based on the currently active user. + + If a language range does not match a known language tag exactly but + does match a language by the rules of [RFC4647], the server MUST send + an untagged LANGUAGE response indicating the language selected. + + If there aren't any arguments, the server SHOULD send an untagged + LANGUAGE response listing the languages it supports. If the server + is unable to enumerate the list of languages it supports it MAY + return a tagged NO response to the enumeration request. If, after + receiving a LANGUAGE request, the server discovers that it doesn't + support any language other than i-default, it MUST return a tagged NO + response to the enumeration request. + + < The server defaults to using English i-default responses until + the user explicitly changes the language. > + + C: A001 LOGIN KAREN PASSWORD + S: A001 OK LOGIN completed + + < Client requested MUL language, which no server supports. > + + C: A002 LANGUAGE MUL + S: A002 NO Unsupported language MUL + + < A LANGUAGE command with no arguments is a request to enumerate + the list of languages the server supports. > + + C: A003 LANGUAGE + S: * LANGUAGE (EN DE IT i-default) + S: A003 OK Supported languages have been enumerated + + C: B001 LANGUAGE + S: B001 NO Server is unable to enumerate supported languages + + + + + + +Newman, et al. Standards Track [Page 5] + +RFC 5255 IMAP Internationalization June 2008 + + + < Once the client changes the language, all responses will be in + that language starting after the LANGUAGE response. Note that + this includes the NAMESPACE response. Because RFCs are in US- + ASCII, this document uses an ASCII transcription rather than + UTF-8 text, e.g., "ue" in the word "ausgefuehrt" > + + C: C001 LANGUAGE DE + S: * LANGUAGE (DE) + S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION" + ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" + "TRANSLATION" ("Gemeinsame Postf&AM8-cher/"))) + S: C001 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt + + < If a server does not support the requested primary language, + responses will continue to be returned in the current language + the server is using. > + + C: D001 LANGUAGE FR + S: D001 NO Diese Sprache ist nicht unterstuetzt + C: D002 LANGUAGE DE-IT + S: * LANGUAGE (DE-IT) + S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION" + ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" + "TRANSLATION" ("Gemeinsame Postf&AM8-cher/"))) + S: D002 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt + C: D003 LANGUAGE "default" + S: * LANGUAGE (DE) + S: D003 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt + + < Server does not speak French, but does speak English. User + speaks Canadian French and Canadian English. > + + C: E001 LANGUAGE FR-CA EN-CA + S: * LANGUAGE (EN) + S: E001 OK Now speaking English + +3.3. LANGUAGE Response + + Contents: A list of one or more language tags. + + The LANGUAGE response occurs as a result of a LANGUAGE command. A + LANGUAGE response with a list containing a single language tag + indicates that the server is now using that language. A LANGUAGE + response with a list containing multiple language tags indicates the + server is communicating a list of available languages to the client, + and no change in the active language has been made. + + + + + +Newman, et al. Standards Track [Page 6] + +RFC 5255 IMAP Internationalization June 2008 + + +3.4. TRANSLATION Extension to the NAMESPACE Response + + If localized representations of the namespace prefixes are available + in the selected language, the server SHOULD include these in the + TRANSLATION extension to the NAMESPACE response. + + The TRANSLATION extension to the NAMESPACE response returns a single + string, containing the modified UTF-7 [RFC3501] encoded translation + of the namespace prefix. It is the responsibility of the client to + convert between the namespace prefix and the translation of the + namespace prefix when presenting mailbox names to the user. + + In this example, a server supports the IMAP4 NAMESPACE command. It + uses no prefix to the user's Personal Namespace, a prefix of "Other + Users" to its Other Users' Namespace, and a prefix of "Public + Folders" to its only Shared Namespace. Since a client will often + display these prefixes to the user, the server includes a translation + of them that can be presented to the user. + + C: A001 LANGUAGE DE-IT + S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION" + ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" + "TRANSLATION" ("Gemeinsame Postf&AM8-cher/"))) + S: A001 OK LANGUAGE-Befehl ausgefuehrt + + + + + + + + + + + + + + + + + + + + + + + + + + + +Newman, et al. Standards Track [Page 7] + +RFC 5255 IMAP Internationalization June 2008 + + +3.5. Formal Syntax + + The following syntax specification inherits ABNF [RFC5234] rules from + IMAP4rev1 [RFC3501], IMAP4 Namespace [RFC2342], Tags for the + Identifying Languages [RFC4646], UTF-8 [RFC3629], and Collected + Extensions to IMAP4 ABNF [RFC4466]. + + command-any =/ language-cmd + ; LANGUAGE command is valid in all states + + language-cmd = "LANGUAGE" *(SP lang-range-quoted) + + response-payload =/ language-data + + language-data = "LANGUAGE" SP "(" lang-tag-quoted *(SP + lang-tag-quoted) ")" + + namespace-trans = SP DQUOTE "TRANSLATION" DQUOTE SP "(" string ")" + ; the string is encoded in Modified UTF-7. + ; this is a subset of the syntax permitted by + ; the Namespace-Response-Extension rule in [RFC4466] + + lang-range-quoted = astring + ; Once any literal wrapper or quoting is removed, this + ; follows the language-range rule in [RFC4647] + + lang-tag-quoted = astring + ; Once any literal wrapper or quoting is removed, this follows + ; the Language-Tag rule in [RFC4646] + + resp-text = ["[" resp-text-code "]" SP ] UTF8-TEXT-CHAR + *(UTF8-TEXT-CHAR / "[") + ; After the server is changed to a language other than + ; i-default, this resp-text rule replaces the resp-text + ; rule from [RFC3501]. + + UTF8-TEXT-CHAR = %x20-5A / %x5C-7E / UTF8-2 / UTF8-3 / UTF8-4 + ; UTF-8 excluding 7-bit control characters and "[" + + + + + + + + + + + + + +Newman, et al. Standards Track [Page 8] + +RFC 5255 IMAP Internationalization June 2008 + + +4. I18NLEVEL=1 and I18NLEVEL=2 Extensions + +4.1. Introduction and Overview + + IMAP4rev1 [RFC3501] includes the SEARCH command that can be used to + locate messages matching criteria including human-readable text. The + SORT extension [SORT] to IMAP allows the client to ask the server to + determine the order of messages based on criteria including human- + readable text. These mechanisms require the ability to support non- + English search and sort functions. + + Section 4 defines two IMAP extensions for internationalizing IMAP + SEARCH, SORT, and THREAD [SORT] using the comparator framework + [RFC4790]. + + The I18NLEVEL=1 extension updates SEARCH/SORT/THREAD to use + i;unicode-casemap comparator, as defined in [UCM]. See Sections 4.2 + and 4.3 for more details. + + The I18NLEVEL=2 extension is a superset of the I18NLEVEL=1 extension. + It adds to I18NLEVEL=1 extension the ability to determine the active + comparator (see definition below) and to negotiate use of comparators + using the COMPARATOR command. It also adds the COMPARATOR response + that indicates the active comparator and possibly other available + comparators. See Sections 4.2 and 4.4 for more details. + +4.2. Requirements Common to Both I18NLEVEL=1 and I18NLEVEL=2 + + The term "default comparator" refers to the comparator that is used + by SEARCH and SORT absent any negotiation using the COMPARATOR + command (see Section 4.7). The term "active comparator" refers to + the comparator which will be used within a session, e.g., by SEARCH + and SORT. The COMPARATOR command is used to change the active + comparator. + + The active comparator applies to the following SEARCH keys: "BCC", + "BODY", "CC", "FROM", "SUBJECT", "TEXT", "TO", and "HEADER". If the + server also advertises the "SORT" extension, then the active + comparator applies to the following SORT keys: "CC", "FROM", + "SUBJECT", and "TO". If the server advertises THREAD=ORDEREDSUBJECT, + then the active comparator applies to the ORDEREDSUBJECT threading + algorithm. If the server advertises THREAD=REFERENCES, then the + active comparator applies to the subject field comparisons done by + REFERENCES threading algorithm. Future extensions may choose to + apply the active comparator to their SEARCH keys. + + + + + + +Newman, et al. Standards Track [Page 9] + +RFC 5255 IMAP Internationalization June 2008 + + + For SORT and THREAD, the pre-processing necessary to extract the base + subject text from a Subject header occurs prior to the application of + a comparator. + + A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST + implement the i;unicode-casemap comparator, as defined in [UCM]. + + A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST + support UTF-8 as a SEARCH charset. + +4.3. I18NLEVEL=1 Extension Requirements + + An IMAP server that satisfies all requirements specified in Sections + 4.2 and 4.6 (and that doesn't support/advertise any other + I18NLEVEL=<n> extension, where n > 1) MUST list the keyword + I18NLEVEL=1 in its CAPABILITY data once IMAP enters the authenticated + state, and MAY list that keyword in other states. + +4.4. I18NLEVEL=2 Extension Requirements + + An IMAP server that satisfies all requirements specified in Sections + 4.2, 4.4, and 4.6-4.10 (and that doesn't support/advertise any other + I18NLEVEL=<n> extension, where n > 2) MUST list the keyword + I18NLEVEL=2 in its CAPABILITY data once IMAP enters the authenticated + state, and MAY list that keyword in other states. + + A server that advertises this extension MUST implement the + i;unicode-casemap comparator, as defined in [UCM]. It MAY implement + other comparators from the IANA registry established by [RFC4790]. + See also Section 4.5 of this document. + + A server that advertises this extension SHOULD use i;unicode-casemap + as the default comparator. (Note that i;unicode-casemap is the + default comparator for I18NLEVEL=1, but not necessarily the default + for I18NLEVEL=2.) The selection of the default comparator MAY be + adjustable by the server administrator, and MAY be sensitive to the + current user. Once the IMAP connection enters authenticated state, + the default comparator MUST remain static for the remainder of that + connection. + + Note that since SEARCH uses the substring operation, IMAP servers can + only implement collations that offer the substring operation (see + [RFC4790], Section 4.2.2). Since SORT uses the ordering operation + (which in turn uses the equality operation), IMAP servers that + advertise the SORT extension can only implement collations that offer + all three operations (see [RFC4790], Sections 4.2.2-4.2.4). + + + + + +Newman, et al. Standards Track [Page 10] + +RFC 5255 IMAP Internationalization June 2008 + + + If the active collation does not provide the operations needed by an + IMAP command, the server MUST respond with a tagged BAD. + +4.5. Compatibility Notes + + Several server implementations deployed prior to the publication of + this specification comply with I18NLEVEL=1 (see Section 4.3), but do + not advertise that. Other legacy servers use the i;ascii-casemap + comparator (see [RFC4790]). + + There is no good way for a client to know which comparator a legacy + server uses. If the client has to assume the worst, it may end up + doing expensive local operations to obtain i;unicode-casemap + comparisons even though the server implements it. + + Legacy server implementations which comply with I18NLEVEL=1 should be + updated to advertise I18NLEVEL=1. All server implementations should + eventually be updated to comply with the I18NLEVEL=2 extension. + +4.6. Comparators and Character Encodings + + RFC 3501, Section 6.4.4, says: + + In all search keys that use strings, a message matches the key + if the string is a substring of the field. The matching is + case-insensitive. + + When performing the SEARCH operation, the active comparator is + applied instead of the case-insensitive matching specified above. + + An IMAP server which performs collation operations (e.g., as part of + commands such as SEARCH, SORT, and THREAD) does so according to the + following procedure: + + (a) MIME encoding (for example, see [RFC2047] for headers and + [RFC2045] for body parts) MUST be removed in the texts being + collated. + + If MIME encoding removal fails for a message (e.g., a body part + of the message has an unsupported Content-Transfer-Encoding, uses + characters not allowed by the Content-Transfer-Encoding, etc.), + the collation of this message is undefined by this specification, + and is handled in an implementation-dependent manner. + + (b) The decoded text from (a) MUST be converted to the charset + expected by the active comparator. + + + + + +Newman, et al. Standards Track [Page 11] + +RFC 5255 IMAP Internationalization June 2008 + + + (c) For the substring operation: + + If step (b) failed (e.g., the text is in an unknown charset, + contains a sequence that is not valid according in that charset, + etc.), the original decoded text from (a) (i.e., before the + charset conversion attempt) is collated using the i;octet + comparator (see [RFC4790]). + + If step (b) was successful, the converted text from (b) is + collated according to the active comparator. + + For the ordering operation: + + All strings that were successfully converted by step (b) are + separated from all strings that failed step (b). Strings in each + group are collated independently. All strings successfully + converted by step (b) are then validated by the active + comparator. Strings that pass validation are collated using the + active comparator. All strings that either fail step (b) or fail + the active collation's validity operation are collated (after + applying step (a)) using the i;octet comparator (see [RFC4790]). + The resulting sorted list is produced by appending all collated + "failed" strings after all strings collated using the active + comparator. + + Example: The following example demonstrates ordering of 4 + different strings using the i;unicode-casemap [UCM] comparator. + Strings are represented using hexadecimal notation used by ABNF + [RFC5234]. + + (1) %xD0 %xC0 %xD0 %xBD %xD0 %xB4 %xD1 %x80 %xD0 %xB5 + %xD0 %xB9 (labeled with charset=UTF-8) + (2) %xD1 %x81 %xD0 %x95 %xD0 %xA0 %xD0 %x93 %xD0 %x95 + %xD0 %x99 (labeled with charset=UTF-8) + (3) %xD0 %x92 %xD0 %xB0 %xD1 %x81 %xD0 %xB8 %xD0 %xBB + %xD0 %xB8 %xFF %xB9 (labeled with charset=UTF-8) + (4) %xE1 %xCC %xC5 %xCB %xD3 %xC5 %xCA (labeled with + charset=KOI8-R) + + Step (b) will convert string (4) to the following sequence of + octets (in UTF-8): + + %xD0 %x90 %xD0 %xBB %xD0 %xB5 %xD0 %xBA %xD1 %x81 %xD0 + %xB5 %xD0 %xB9 + + and will reject strings (1) and (3), as they contain octets not + allowed in charset=UTF-8. + + + + +Newman, et al. Standards Track [Page 12] + +RFC 5255 IMAP Internationalization June 2008 + + + After that, using the i;unicode-casemap collation, string (4) + will collate before string (2). Using the i;octet collation on + the original strings, string (3) will collate before string (1). + So the final ordering is as follows: (4) (2) (3) (1). + + If the substring operation (e.g., IMAP SEARCH) of the active + comparator returns the "undefined" result (see Section 4.2.3 of + [RFC4790]) for either the text specified in the SEARCH command or the + message text, then the operation is repeated on the result of step + (a) using the i;octet comparator. + + The ordering operation (e.g., IMAP SORT and THREAD) SHOULD collate + the following together: strings encoded using unknown or invalid + character encodings, strings in unrecognized charsets, and invalid + input (as defined by the active collation). + +4.7. COMPARATOR Command + + Arguments: Optional comparator order arguments. + + Response: A possible COMPARATOR response (see Section 4.8). + + Result: OK - Command completed + NO - No matching comparator found + BAD - Arguments invalid + + The COMPARATOR command is valid in authenticated and selected states. + + The COMPARATOR command is used to determine or change the active + comparator. When issued with no arguments, it results in a + COMPARATOR response indicating the currently active comparator. + + When issued with one or more comparator arguments, it changes the + active comparator as directed. (If more than one installed + comparator is matched by an argument, the first argument wins.) The + COMPARATOR response lists all matching comparators if more than one + matches the specified patterns. + + The argument "default" refers to the server's default comparator. + Otherwise, each argument is a collation specification as defined in + the Internet Application Protocol Comparator Registry [RFC4790]. + + < The client requests activating a Czech comparator if possible, + or else a generic international comparator which it considers + suitable for Czech. The server picks the first supported + comparator. > + + + + + +Newman, et al. Standards Track [Page 13] + +RFC 5255 IMAP Internationalization June 2008 + + + C: A001 COMPARATOR "cz;*" i;basic + S: * COMPARATOR i;basic + S: A001 OK Will use i;basic for collation + +4.8. COMPARATOR Response + + Contents: The active comparator. An optional list of available + matching comparators + + The COMPARATOR response occurs as a result of a COMPARATOR command. + The first argument in the comparator response is the name of the + active comparator. The second argument is a list of comparators + which matched any of the arguments to the COMPARATOR command and is + present only if more than one match is found. + +4.9. BADCOMPARATOR Response Code + + This response code SHOULD be returned as a result of server failing + an IMAP command (returning NO), when the server knows that none of + the specified comparators match the requested comparator(s). + +4.10. Formal Syntax + + The following syntax specification inherits ABNF [RFC5234] rules from + IMAP4rev1 [RFC3501] and the Internet Application Protocol Comparator + Registry [RFC4790]. + + command-auth =/ comparator-cmd + + resp-text-code =/ "BADCOMPARATOR" + + comparator-cmd = "COMPARATOR" *(SP comp-order-quoted) + + response-payload =/ comparator-data + + comparator-data = "COMPARATOR" SP comp-sel-quoted [SP "(" + comp-id-quoted *(SP comp-id-quoted) ")"] + + comp-id-quoted = astring + ; Once any literal wrapper or quoting is removed, this + ; follows the collation-id rule from [RFC4790] + + comp-order-quoted = astring + ; Once any literal wrapper or quoting is removed, this + ; follows the collation-order rule from [RFC4790] + + + + + + +Newman, et al. Standards Track [Page 14] + +RFC 5255 IMAP Internationalization June 2008 + + + comp-sel-quoted = astring + ; Once any literal wrapper or quoting is removed, this + ; follows the collation-selected rule from [RFC4790] + +5. Other IMAP Internationalization Issues + + The following sections provide an overview of various other IMAP + internationalization issues. These issues are not resolved by this + specification, but could be resolved by other standards work, such as + that being done by the EAI working group (see [IMAP-EAI]). + +5.1. Unicode Userids and Passwords + + IMAP4rev1 currently restricts the userid and password fields of the + LOGIN command to US-ASCII. The "userid" and "password" fields of the + IMAP LOGIN command are restricted to US-ASCII only until a future + standards track RFC states otherwise. Servers are encouraged to + validate both fields to make sure they conform to the formal syntax + of UTF-8 and to reject the LOGIN command if that syntax is violated. + Servers MAY reject the LOGIN command if either the "userid" or + "password" field contains an octet with the highest bit set. + + When AUTHENTICATE is used, some servers may support userids and + passwords in Unicode [RFC3490] since SASL (see [RFC4422]) allows + that. However, such userids cannot be used as part of email + addresses. + +5.2. UTF-8 Mailbox Names + + The modified UTF-7 mailbox naming convention described in Section + 5.1.3 of RFC 3501 is best viewed as an transition from the status quo + in 1996 when modified UTF-7 was first specified. At that time, there + was widespread unofficial use of local character sets such as ISO- + 8859-1 and Shift-JIS for non-ASCII mailbox names, with resultant + non-interoperability. + + The requirements in Section 5.1 of RFC 3501 are very important if + we're ever going to be able to deploy UTF-8 mailbox names. Servers + are encouraged to enforce them. + +5.3. UTF-8 Domains, Addresses, and Mail Headers + + There is now an IETF standard for "Internationalizing Domain Names in + Applications (IDNA)" [RFC3490]. While IMAP clients are free to + support this standard, an argument can be made that it would be + helpful to simple clients if the IMAP server could perform this + conversion (the same argument would apply to MIME header encoding + + + + +Newman, et al. Standards Track [Page 15] + +RFC 5255 IMAP Internationalization June 2008 + + + [RFC2047]). However, it would be unwise to move forward with such + work until the work in progress to define the format of international + email addresses is complete. + +6. IANA Considerations + + IANA added LANGUAGE, I18NLEVEL=1, and I18NLEVEL=2 to the IMAP4 + Capabilities Registry. + +7. Security Considerations + + The LANGUAGE extension makes a new command available in "Not + Authenticated" state in IMAP. Some IMAP implementations run with + root privilege when the server is in "Not Authenticated" state and do + not revoke that privilege until after authentication is complete. + Such implementations are particularly vulnerable to buffer overflow + security errors at this stage and need to implement parsing of this + command with extra care. + + A LANGUAGE command issued prior to activation of a security layer is + subject to an active attack that suppresses or modifies the + negotiation, and thus makes STARTTLS or authentication error messages + more difficult to interpret. This is not a new attack as the error + messages themselves are subject to active attack. Clients MUST re- + issue the LANGUAGE command once a security layer is active, in order + to prevent this attack from impacting subsequent protocol operations. + + LANGUAGE, I18NLEVEL=1, and I18NLEVEL=2 extensions use the UTF-8 + charset; thus, the security considerations for UTF-8 [RFC3629] are + relevant. However, neither uses UTF-8 for identifiers, so the most + serious concerns do not apply. + +8. Acknowledgements + + The LANGUAGE extension is based on a previous document by Mike + Gahrns, a substantial portion of the text in that section was written + by him. Many people have participated in discussions about an IMAP + Language extension in the various fora of the IETF and Internet + working groups, so any list of contributors is bound to be + incomplete. However, the authors would like to thank Andrew McCown + for early work on the original proposal, John Myers for suggestions + regarding the namespace issue, along with Jutta Degener, Mark + Crispin, Mark Pustilnik, Larry Osterman, Cyrus Daboo, Martin Duerst, + Timo Sirainen, Ben Campbell, and Magnus Nystrom for their many + suggestions that have been incorporated into this document. + + Initial discussion of the I18NLEVEL=2 extension involved input from + Mark Crispin and other participants of the IMAP Extensions WG. + + + +Newman, et al. Standards Track [Page 16] + +RFC 5255 IMAP Internationalization June 2008 + + +9. Relevant Sources of Documents for Internationalized IMAP + Implementations + + This is a non-normative list of sources to consider when implementing + i18n-aware IMAP software. + + o The LANGUAGE and I18NLEVEL=2 extensions to IMAP (this + specification). + + o The 8-bit rules for mailbox naming in Section 5.1 of RFC 3501. + + o The Mailbox International Naming Convention in Section 5.1.3 of + RFC 3501. + + o MIME [RFC2045] for message bodies. + + o MIME header encoding [RFC2047] for message headers. + + o The IETF EAI working group. + + o MIME Parameter Value and Encoded Word Extensions [RFC2231] for + filenames. Quality IMAP server implementations will + automatically combine multipart parameters when generating the + BODYSTRUCTURE. There is also some deployed non-standard use of + MIME header encoding inside double quotes for filenames. + + o IDNA [RFC3490] and punycode [RFC3492] for domain names + (currently only relevant to IMAP clients). + + o The UTF-8 charset [RFC3629]. + + o The IETF policy on Character Sets and Languages [RFC2277]. + +10. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and + Languages", BCP 18, RFC 2277, January 1998. + + [RFC2342] Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342, May + 1998. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + + + + +Newman, et al. Standards Track [Page 17] + +RFC 5255 IMAP Internationalization June 2008 + + + [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO + 10646", STD 63, RFC 3629, November 2003. + + [RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", STD 68, RFC 5234, January + 2008. + + [RFC4422] Melnikov, A., Ed., and K. Zeilenga, Ed., "Simple + Authentication and Security Layer (SASL)", RFC 4422, June + 2006. + + [RFC4466] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4 + ABNF", RFC 4466, April 2006. + + [RFC4646] Phillips, A. and M. Davis, "Tags for Identifying + Languages", BCP 47, RFC 4646, September 2006. + + [RFC4647] Phillips, A. and M. Davis, "Matching of Language Tags", + BCP 47, RFC 4647, September 2006. + + [RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet + Application Protocol Collation Registry", RFC 4790, March + 2007. + + [SORT] Crispin, M. and K. Murchison, "Internet Message Access + Protocol - SORT and THREAD Extensions", RFC 5256, June + 2008. + + [UCM] Crispin, M., "i;unicode-casemap - Simple Unicode Collation + Algorithm", RFC 5051, October 2007. + + [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail + Extensions (MIME) Part One: Format of Internet Message + Bodies", RFC 2045, November 1996. + + [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) + Part Three: Message Header Extensions for Non-ASCII Text", + RFC 2047, November 1996. + +11. Informative References + + [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded + Word Extensions: Character Sets, Languages, and + Continuations", RFC 2231, November 1997. + + [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, + "Internationalizing Domain Names in Applications (IDNA)", + RFC 3490, March 2003. + + + +Newman, et al. Standards Track [Page 18] + +RFC 5255 IMAP Internationalization June 2008 + + + [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode + for Internationalized Domain Names in Applications + (IDNA)", RFC 3492, March 2003. + + [METADATA] Daboo, C., "IMAP METADATA Extension", Work in Progress, + April 2008. + + [IMAP-EAI] Resnick, P., and C. Newman, "IMAP Support for UTF-8", Work + in Progress, November 2007. + +Authors' Addresses + + Chris Newman + Sun Microsystems + 3401 Centrelake Dr., Suite 410 + Ontario, CA 91761 + US + + EMail: chris.newman@sun.com + + + Arnt Gulbrandsen + Oryx Mail Systems GmbH + Schweppermannstr. 8 + D-81671 Muenchen + Germany + + EMail: arnt@oryx.com + Fax: +49 89 4502 9758 + + + Alexey Melnikov + Isode Limited + 5 Castle Business Village, 36 Station Road, + Hampton, Middlesex, TW12 2BX, UK + + EMail: Alexey.Melnikov@isode.com + + + + + + + + + + + + + + +Newman, et al. Standards Track [Page 19] + +RFC 5255 IMAP Internationalization June 2008 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2008). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Newman, et al. Standards Track [Page 20] + diff --git a/imap/docs/rfc/rfc5256.txt b/imap/docs/rfc/rfc5256.txt new file mode 100644 index 00000000..fff0591a --- /dev/null +++ b/imap/docs/rfc/rfc5256.txt @@ -0,0 +1,1067 @@ + + + + + + +Network Working Group M. Crispin +Request for Comments: 5256 Panda Programming +Category: Standards Track K. Murchison + Carnegie Mellon University + June 2008 + + + Internet Message Access Protocol - SORT and THREAD Extensions + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + This document describes the base-level server-based sorting and + threading extensions to the IMAP protocol. These extensions provide + substantial performance improvements for IMAP clients that offer + sorted and threaded views. + +1. Introduction + + The SORT and THREAD extensions to the [IMAP] protocol provide a means + of server-based sorting and threading of messages, without requiring + that the client download the necessary data to do so itself. This is + particularly useful for online clients as described in [IMAP-MODELS]. + + A server that supports the base-level SORT extension indicates this + with a capability name which starts with "SORT". Future, upwards- + compatible extensions to the SORT extension will all start with + "SORT", indicating support for this base level. + + A server that supports the THREAD extension indicates this with one + or more capability names consisting of "THREAD=" followed by a + supported threading algorithm name as described in this document. + This provides for future upwards-compatible extensions. + + A server that implements the SORT and/or THREAD extensions MUST + collate strings in accordance with the requirements of I18NLEVEL=1, + as described in [IMAP-I18N], and SHOULD implement and advertise the + I18NLEVEL=1 extension. Alternatively, a server MAY implement + I18NLEVEL=2 (or higher) and comply with the rules of that level. + + + + + +Crispin & Murchison Standards Track [Page 1] + +RFC 5256 IMAP Sort June 2008 + + + Discussion: The SORT and THREAD extensions predate [IMAP-I18N] by + several years. At the time of this writing, all known server + implementations of SORT and THREAD comply with the rules of + I18NLEVEL=1, but do not necessarily advertise it. As discussed in + [IMAP-I18N] section 4.5, all server implementations should + eventually be updated to comply with the I18NLEVEL=2 extension. + + Historical note: The REFERENCES threading algorithm is based on the + [THREADING] algorithm written and used in "Netscape Mail and News" + versions 2.0 through 3.0. + +2. Terminology + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [KEYWORDS]. + + The word "can" (not "may") is used to refer to a possible + circumstance or situation, as opposed to an optional facility of the + protocol. + + "User" is used to refer to a human user, whereas "client" refers to + the software being run by the user. + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. + +2.1. Base Subject + + Subject sorting and threading use the "base subject", which has + specific subject artifacts removed. Due to the complexity of these + artifacts, the formal syntax for the subject extraction rules is + ambiguous. The following procedure is followed to determine the + "base subject", using the [ABNF] formal syntax rules described in + section 5: + + (1) Convert any RFC 2047 encoded-words in the subject to [UTF-8] + as described in "Internationalization Considerations". + Convert all tabs and continuations to space. Convert all + multiple spaces to a single space. + + (2) Remove all trailing text of the subject that matches the + subj-trailer ABNF; repeat until no more matches are possible. + + (3) Remove all prefix text of the subject that matches the subj- + leader ABNF. + + + + + +Crispin & Murchison Standards Track [Page 2] + +RFC 5256 IMAP Sort June 2008 + + + (4) If there is prefix text of the subject that matches the subj- + blob ABNF, and removing that prefix leaves a non-empty subj- + base, then remove the prefix text. + + (5) Repeat (3) and (4) until no matches remain. + + Note: It is possible to defer step (2) until step (6), but this + requires checking for subj-trailer in step (4). + + (6) If the resulting text begins with the subj-fwd-hdr ABNF and + ends with the subj-fwd-trl ABNF, remove the subj-fwd-hdr and + subj-fwd-trl and repeat from step (2). + + (7) The resulting text is the "base subject" used in the SORT. + + All servers and disconnected (as described in [IMAP-MODELS]) clients + MUST use exactly this algorithm to determine the "base subject". + Otherwise, there is potential for a user to get inconsistent results + based on whether they are running in connected or disconnected mode. + +2.2. Sent Date + + As used in this document, the term "sent date" refers to the date and + time from the Date: header, adjusted by time zone to normalize to + UTC. For example, "31 Dec 2000 16:01:33 -0800" is equivalent to the + UTC date and time of "1 Jan 2001 00:01:33 +0000". + + If the time zone is invalid, the date and time SHOULD be treated as + UTC. If the time is also invalid, the time SHOULD be treated as + 00:00:00. If there is no valid date or time, the date and time + SHOULD be treated as 00:00:00 on the earliest possible date. + + This differs from the date-related criteria in the SEARCH command + (described in [IMAP] section 6.4.4), which use just the date and not + the time, and are not adjusted by time zone. + + If the sent date cannot be determined (a Date: header is missing or + cannot be parsed), the INTERNALDATE for that message is used as the + sent date. + + When comparing two sent dates that match exactly, the order in which + the two messages appear in the mailbox (that is, by sequence number) + is used as a tie-breaker to determine the order. + + + + + + + + +Crispin & Murchison Standards Track [Page 3] + +RFC 5256 IMAP Sort June 2008 + + +3. Additional Commands + + These commands are extensions to the [IMAP] base protocol. + + The section headings are intended to correspond with where they would + be located in the main document if they were part of the base + specification. + +BASE.6.4.SORT. SORT Command + + Arguments: sort program + charset specification + searching criteria (one or more) + + Data: untagged responses: SORT + + Result: OK - sort completed + NO - sort error: can't sort that charset or + criteria + BAD - command unknown or arguments invalid + + The SORT command is a variant of SEARCH with sorting semantics for + the results. There are two arguments before the searching + criteria argument: a parenthesized list of sort criteria, and the + searching charset. + + The charset argument is mandatory (unlike SEARCH) and indicates + the [CHARSET] of the strings that appear in the searching + criteria. The US-ASCII and [UTF-8] charsets MUST be implemented. + All other charsets are optional. + + There is also a UID SORT command that returns unique identifiers + instead of message sequence numbers. Note that there are separate + searching criteria for message sequence numbers and UIDs; thus, + the arguments to UID SORT are interpreted the same as in SORT. + This is analogous to the behavior of UID SEARCH, as opposed to UID + COPY, UID FETCH, or UID STORE. + + The SORT command first searches the mailbox for messages that + match the given searching criteria using the charset argument for + the interpretation of strings in the searching criteria. It then + returns the matching messages in an untagged SORT response, sorted + according to one or more sort criteria. + + Sorting is in ascending order. Earlier dates sort before later + dates; smaller sizes sort before larger sizes; and strings are + sorted according to ascending values established by their + collation algorithm (see "Internationalization Considerations"). + + + +Crispin & Murchison Standards Track [Page 4] + +RFC 5256 IMAP Sort June 2008 + + + If two or more messages exactly match according to the sorting + criteria, these messages are sorted according to the order in + which they appear in the mailbox. In other words, there is an + implicit sort criterion of "sequence number". + + When multiple sort criteria are specified, the result is sorted in + the priority order that the criteria appear. For example, + (SUBJECT DATE) will sort messages in order by their base subject + text; and for messages with the same base subject text, it will + sort by their sent date. + + Untagged EXPUNGE responses are not permitted while the server is + responding to a SORT command, but are permitted during a UID SORT + command. + + The defined sort criteria are as follows. Refer to the Formal + Syntax section for the precise syntactic definitions of the + arguments. If the associated RFC-822 header for a particular + criterion is absent, it is treated as the empty string. The empty + string always collates before non-empty strings. + + ARRIVAL + Internal date and time of the message. This differs from the + ON criteria in SEARCH, which uses just the internal date. + + CC + [IMAP] addr-mailbox of the first "cc" address. + + DATE + Sent date and time, as described in section 2.2. + + FROM + [IMAP] addr-mailbox of the first "From" address. + + REVERSE + Followed by another sort criterion, has the effect of that + criterion but in reverse (descending) order. + Note: REVERSE only reverses a single criterion, and does not + affect the implicit "sequence number" sort criterion if all + other criteria are identical. Consequently, a sort of + REVERSE SUBJECT is not the same as a reverse ordering of a + SUBJECT sort. This can be avoided by use of additional + criteria, e.g., SUBJECT DATE vs. REVERSE SUBJECT REVERSE + DATE. In general, however, it's better (and faster, if the + client has a "reverse current ordering" command) to reverse + the results in the client instead of issuing a new SORT. + + + + + +Crispin & Murchison Standards Track [Page 5] + +RFC 5256 IMAP Sort June 2008 + + + SIZE + Size of the message in octets. + + SUBJECT + Base subject text. + + TO + [IMAP] addr-mailbox of the first "To" address. + + Example: C: A282 SORT (SUBJECT) UTF-8 SINCE 1-Feb-1994 + S: * SORT 2 84 882 + S: A282 OK SORT completed + C: A283 SORT (SUBJECT REVERSE DATE) UTF-8 ALL + S: * SORT 5 3 4 1 2 + S: A283 OK SORT completed + C: A284 SORT (SUBJECT) US-ASCII TEXT "not in mailbox" + S: * SORT + S: A284 OK SORT completed + +BASE.6.4.THREAD. THREAD Command + +Arguments: threading algorithm + charset specification + searching criteria (one or more) + +Data: untagged responses: THREAD + +Result: OK - thread completed + NO - thread error: can't thread that charset or + criteria + BAD - command unknown or arguments invalid + + The THREAD command is a variant of SEARCH with threading semantics + for the results. Thread has two arguments before the searching + criteria argument: a threading algorithm and the searching + charset. + + The charset argument is mandatory (unlike SEARCH) and indicates + the [CHARSET] of the strings that appear in the searching + criteria. The US-ASCII and [UTF-8] charsets MUST be implemented. + All other charsets are optional. + + There is also a UID THREAD command that returns unique identifiers + instead of message sequence numbers. Note that there are separate + searching criteria for message sequence numbers and UIDs; thus the + arguments to UID THREAD are interpreted the same as in THREAD. + This is analogous to the behavior of UID SEARCH, as opposed to UID + COPY, UID FETCH, or UID STORE. + + + +Crispin & Murchison Standards Track [Page 6] + +RFC 5256 IMAP Sort June 2008 + + + The THREAD command first searches the mailbox for messages that + match the given searching criteria using the charset argument for + the interpretation of strings in the searching criteria. It then + returns the matching messages in an untagged THREAD response, + threaded according to the specified threading algorithm. + + All collation is in ascending order. Earlier dates collate before + later dates and strings are collated according to ascending values + established by their collation algorithm (see + "Internationalization Considerations"). + + Untagged EXPUNGE responses are not permitted while the server is + responding to a THREAD command, but are permitted during a UID + THREAD command. + + The defined threading algorithms are as follows: + + ORDEREDSUBJECT + + The ORDEREDSUBJECT threading algorithm is also referred to as + "poor man's threading". The searched messages are sorted by + base subject and then by the sent date. The messages are then + split into separate threads, with each thread containing + messages with the same base subject text. Finally, the threads + are sorted by the sent date of the first message in the thread. + + The top level or "root" in ORDEREDSUBJECT threading contains + the first message of every thread. All messages in the root + are siblings of each other. The second message of a thread is + the child of the first message, and subsequent messages of the + thread are siblings of the second message and hence children of + the message at the root. Hence, there are no grandchildren in + ORDEREDSUBJECT threading. + + Children in ORDEREDSUBJECT threading do not have descendents. + Client implementations SHOULD treat descendents of a child in a + server response as being siblings of that child. + + REFERENCES + + The REFERENCES threading algorithm threads the searched + messages by grouping them together in parent/child + relationships based on which messages are replies to others. + The parent/child relationships are built using two methods: + reconstructing a message's ancestry using the references + contained within it; and checking the original (not base) + subject of a message to see if it is a reply to (or forward of) + another message. + + + +Crispin & Murchison Standards Track [Page 7] + +RFC 5256 IMAP Sort June 2008 + + + Note: "Message ID" in the following description refers to a + normalized form of the msg-id in [RFC2822]. The actual text + in RFC 2822 may use quoting, resulting in multiple ways of + expressing the same Message ID. Implementations of the + REFERENCES threading algorithm MUST normalize any msg-id in + order to avoid false non-matches due to differences in + quoting. + + For example, the msg-id + <"01KF8JCEOCBS0045PS"@xxx.yyy.com> + and the msg-id + <01KF8JCEOCBS0045PS@xxx.yyy.com> + MUST be interpreted as being the same Message ID. + + The references used for reconstructing a message's ancestry are + found using the following rules: + + If a message contains a References header line, then use the + Message IDs in the References header line as the references. + + If a message does not contain a References header line, or + the References header line does not contain any valid + Message IDs, then use the first (if any) valid Message ID + found in the In-Reply-To header line as the only reference + (parent) for this message. + + Note: Although [RFC2822] permits multiple Message IDs in + the In-Reply-To header, in actual practice this + discipline has not been followed. For example, + In-Reply-To headers have been observed with message + addresses after the Message ID, and there are no good + heuristics for software to determine the difference. + This is not a problem with the References header, + however. + + If a message does not contain an In-Reply-To header line, or + the In-Reply-To header line does not contain a valid Message + ID, then the message does not have any references (NIL). + + A message is considered to be a reply or forward if the base + subject extraction rules, applied to the original subject, + remove any of the following: a subj-refwd, a "(fwd)" subj- + trailer, or a subj-fwd-hdr and subj-fwd-trl. + + The REFERENCES algorithm is significantly more complex than + ORDEREDSUBJECT and consists of six main steps. These steps are + outlined in detail below. + + + + +Crispin & Murchison Standards Track [Page 8] + +RFC 5256 IMAP Sort June 2008 + + + (1) For each searched message: + + (A) Using the Message IDs in the message's references, link + the corresponding messages (those whose Message-ID + header line contains the given reference Message ID) + together as parent/child. Make the first reference the + parent of the second (and the second a child of the + first), the second the parent of the third (and the + third a child of the second), etc. The following rules + govern the creation of these links: + + If a message does not contain a Message-ID header + line, or the Message-ID header line does not + contain a valid Message ID, then assign a unique + Message ID to this message. + + If two or more messages have the same Message ID, + then only use that Message ID in the first (lowest + sequence number) message, and assign a unique + Message ID to each of the subsequent messages with + a duplicate of that Message ID. + + If no message can be found with a given Message ID, + create a dummy message with this ID. Use this + dummy message for all subsequent references to this + ID. + + If a message already has a parent, don't change the + existing link. This is done because the References + header line may have been truncated by a Mail User + Agent (MUA). As a result, there is no guarantee + that the messages corresponding to adjacent Message + IDs in the References header line are parent and + child. + + Do not create a parent/child link if creating that + link would introduce a loop. For example, before + making message A the parent of B, make sure that A + is not a descendent of B. + + Note: Message ID comparisons are case-sensitive. + + (B) Create a parent/child link between the last reference + (or NIL if there are no references) and the current + message. If the current message already has a parent, + it is probably the result of a truncated References + header line, so break the current parent/child link + before creating the new correct one. As in step 1.A, + + + +Crispin & Murchison Standards Track [Page 9] + +RFC 5256 IMAP Sort June 2008 + + + do not create the parent/child link if creating that + link would introduce a loop. Note that if this message + has no references, it will now have no parent. + + Note: The parent/child links created in steps 1.A + and 1.B MUST be kept consistent with one another at + ALL times. + + (2) Gather together all of the messages that have no parents + and make them all children (siblings of one another) of a + dummy parent (the "root"). These messages constitute the + first (head) message of the threads created thus far. + + (3) Prune dummy messages from the thread tree. Traverse each + thread under the root, and for each message: + + If it is a dummy message with NO children, delete it. + + If it is a dummy message with children, delete it, but + promote its children to the current level. In other + words, splice them in with the dummy's siblings. + + Do not promote the children if doing so would make them + children of the root, unless there is only one child. + + (4) Sort the messages under the root (top-level siblings only) + by sent date as described in section 2.2. In the case of a + dummy message, sort its children by sent date and then use + the first child for the top-level sort. + + (5) Gather together messages under the root that have the same + base subject text. + + (A) Create a table for associating base subjects with + messages, called the subject table. + + (B) Populate the subject table with one message per each + base subject. For each child of the root: + + (i) Find the subject of this thread, by using the + base subject from either the current message or + its first child if the current message is a + dummy. This is the thread subject. + + (ii) If the thread subject is empty, skip this + message. + + + + + +Crispin & Murchison Standards Track [Page 10] + +RFC 5256 IMAP Sort June 2008 + + + (iii) Look up the message associated with the thread + subject in the subject table. + + (iv) If there is no message in the subject table with + the thread subject, add the current message and + the thread subject to the subject table. + + Otherwise, if the message in the subject table is + not a dummy, AND either of the following criteria + are true: + + The current message is a dummy, OR + + The message in the subject table is a reply + or forward and the current message is not. + + then replace the message in the subject table + with the current message. + + (C) Merge threads with the same thread subject. For each + child of the root: + + (i) Find the message's thread subject as in step + 5.B.i above. + + (ii) If the thread subject is empty, skip this + message. + + (iii) Lookup the message associated with this thread + subject in the subject table. + + (iv) If the message in the subject table is the + current message, skip this message. + + Otherwise, merge the current message with the one in + the subject table using the following rules: + + If both messages are dummies, append the current + message's children to the children of the message + in the subject table (the children of both messages + become siblings), and then delete the current + message. + + If the message in the subject table is a dummy and + the current message is not, make the current + message a child of the message in the subject table + (a sibling of its children). + + + + +Crispin & Murchison Standards Track [Page 11] + +RFC 5256 IMAP Sort June 2008 + + + If the current message is a reply or forward and + the message in the subject table is not, make the + current message a child of the message in the + subject table (a sibling of its children). + + Otherwise, create a new dummy message and make both + the current message and the message in the subject + table children of the dummy. Then replace the + message in the subject table with the dummy + message. + + Note: Subject comparisons are case-insensitive, + as described under "Internationalization + Considerations". + + (6) Traverse the messages under the root and sort each set of + siblings by sent date as described in section 2.2. + Traverse the messages in such a way that the "youngest" set + of siblings are sorted first, and the "oldest" set of + siblings are sorted last (grandchildren are sorted before + children, etc). In the case of a dummy message (which can + only occur with top-level siblings), use its first child + for sorting. + + Example: C: A283 THREAD ORDEREDSUBJECT UTF-8 SINCE 5-MAR-2000 + S: * THREAD (166)(167)(168)(169)(172)(170)(171) + (173)(174 (175)(176)(178)(181)(180))(179)(177 + (183)(182)(188)(184)(185)(186)(187)(189))(190) + (191)(192)(193)(194 195)(196 (197)(198))(199) + (200 202)(201)(203)(204)(205)(206 207)(208) + S: A283 OK THREAD completed + C: A284 THREAD ORDEREDSUBJECT US-ASCII TEXT "gewp" + S: * THREAD + S: A284 OK THREAD completed + C: A285 THREAD REFERENCES UTF-8 SINCE 5-MAR-2000 + S: * THREAD (166)(167)(168)(169)(172)((170)(179)) + (171)(173)((174)(175)(176)(178)(181)(180)) + ((177)(183)(182)(188 (184)(189))(185 186)(187)) + (190)(191)(192)(193)((194)(195 196))(197 198) + (199)(200 202)(201)(203)(204)(205 206 207)(208) + S: A285 OK THREAD completed + + Note: The line breaks in the first and third server + responses are for editorial clarity and do not appear in + real THREAD responses. + + + + + + +Crispin & Murchison Standards Track [Page 12] + +RFC 5256 IMAP Sort June 2008 + + +4. Additional Responses + + These responses are extensions to the [IMAP] base protocol. + + The section headings of these responses are intended to correspond + with where they would be located in the main document. + +BASE.7.2.SORT. SORT Response + + Data: zero or more numbers + + The SORT response occurs as a result of a SORT or UID SORT + command. The number(s) refer to those messages that match the + search criteria. For SORT, these are message sequence numbers; + for UID SORT, these are unique identifiers. Each number is + delimited by a space. + + Example: S: * SORT 2 3 6 + +BASE.7.2.THREAD. THREAD Response + + Data: zero or more threads + + The THREAD response occurs as a result of a THREAD or UID THREAD + command. It contains zero or more threads. A thread consists of + a parenthesized list of thread members. + + Thread members consist of zero or more message numbers, delimited + by spaces, indicating successive parent and child. This continues + until the thread splits into multiple sub-threads, at which point, + the thread nests into multiple sub-threads with the first member + of each sub-thread being siblings at this level. There is no + limit to the nesting of threads. + + The messages numbers refer to those messages that match the search + criteria. For THREAD, these are message sequence numbers; for UID + THREAD, these are unique identifiers. + + Example: S: * THREAD (2)(3 6 (4 23)(44 7 96)) + + The first thread consists only of message 2. The second thread + consists of the messages 3 (parent) and 6 (child), after which it + splits into two sub-threads; the first of which contains messages + 4 (child of 6, sibling of 44) and 23 (child of 4), and the second + of which contains messages 44 (child of 6, sibling of 4), 7 (child + of 44), and 96 (child of 7). Since some later messages are + parents of earlier messages, the messages were probably moved from + some other mailbox at different times. + + + +Crispin & Murchison Standards Track [Page 13] + +RFC 5256 IMAP Sort June 2008 + + + -- 2 + + -- 3 + \-- 6 + |-- 4 + | \-- 23 + | + \-- 44 + \-- 7 + \-- 96 + + Example: S: * THREAD ((3)(5)) + + In this example, 3 and 5 are siblings of a parent that does not + match the search criteria (and/or does not exist in the mailbox); + however they are members of the same thread. + +5. Formal Syntax of SORT and THREAD Commands and Responses + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [ABNF]. It also uses [ABNF] + rules defined in [IMAP]. + +sort = ["UID" SP] "SORT" SP sort-criteria SP search-criteria + +sort-criteria = "(" sort-criterion *(SP sort-criterion) ")" + +sort-criterion = ["REVERSE" SP] sort-key + +sort-key = "ARRIVAL" / "CC" / "DATE" / "FROM" / "SIZE" / + "SUBJECT" / "TO" + +thread = ["UID" SP] "THREAD" SP thread-alg SP search-criteria + +thread-alg = "ORDEREDSUBJECT" / "REFERENCES" / thread-alg-ext + +thread-alg-ext = atom + ; New algorithms MUST be registered with IANA + +search-criteria = charset 1*(SP search-key) + +charset = atom / quoted + ; CHARSET values MUST be registered with IANA + +sort-data = "SORT" *(SP nz-number) + +thread-data = "THREAD" [SP 1*thread-list] + + + + +Crispin & Murchison Standards Track [Page 14] + +RFC 5256 IMAP Sort June 2008 + + +thread-list = "(" (thread-members / thread-nested) ")" + +thread-members = nz-number *(SP nz-number) [SP thread-nested] + +thread-nested = 2*thread-list + + The following syntax describes base subject extraction rules (2)-(6): + +subject = *subj-leader [subj-middle] *subj-trailer + +subj-refwd = ("re" / ("fw" ["d"])) *WSP [subj-blob] ":" + +subj-blob = "[" *BLOBCHAR "]" *WSP + +subj-fwd = subj-fwd-hdr subject subj-fwd-trl + +subj-fwd-hdr = "[fwd:" + +subj-fwd-trl = "]" + +subj-leader = (*subj-blob subj-refwd) / WSP + +subj-middle = *subj-blob (subj-base / subj-fwd) + ; last subj-blob is subj-base if subj-base would + ; otherwise be empty + +subj-trailer = "(fwd)" / WSP + +subj-base = NONWSP *(*WSP NONWSP) + ; can be a subj-blob + +BLOBCHAR = %x01-5a / %x5c / %x5e-ff + ; any CHAR8 except '[' and ']'. + ; SHOULD comply with [UTF-8] + +NONWSP = %x01-08 / %x0a-1f / %x21-ff + ; any CHAR8 other than WSP. + ; SHOULD comply with [UTF-8] + +6. Security Considerations + + The SORT and THREAD extensions do not raise any security + considerations that are not present in the base [IMAP] protocol, and + these issues are discussed in [IMAP]. Nevertheless, it is important + to remember that [IMAP] protocol transactions, including message + data, are sent in the clear over the network unless protection from + snooping is negotiated, either by the use of STARTTLS, privacy + protection in AUTHENTICATE, or some other protection mechanism. + + + +Crispin & Murchison Standards Track [Page 15] + +RFC 5256 IMAP Sort June 2008 + + + Although not a security consideration, it is important to recognize + that sorting by REFERENCES can lead to misleading threading trees. + For example, a message with false References: header data will cause + a thread to be incorporated into another thread. + + The process of extracting the base subject may lead to incorrect + collation if the extracted data was significant text as opposed to a + subject artifact. + +7. Internationalization Considerations + + As stated in the introduction, the rules of I18NLEVEL=1 as described + in [IMAP-I18N] MUST be followed; that is, the SORT and THREAD + extensions MUST collate strings according to the i;unicode-casemap + collation described in [UNICASEMAP]. Servers SHOULD also advertise + the I18NLEVEL=1 extension. Alternatively, a server MAY implement + I18NLEVEL=2 (or higher) and comply with the rules of that level. + + As discussed in [IMAP-I18N] section 4.5, all server implementations + should eventually be updated to support the [IMAP-I18N] I18NLEVEL=2 + extension. + + Translations of the "re" or "fw"/"fwd" tokens are not specified for + removal in the base subject extraction process. An attempt to add + such translated tokens would result in a geometrically complex, and + ultimately unimplementable, task. + + Instead, note that [RFC2822] section 3.6.5 recommends that "re:" + (from the Latin "res", meaning "in the matter of") be used to + identify a reply. Although it is evident that, from the multiple + forms of token to identify a forwarded message, there is considerable + variation found in the wild, the variations are (still) manageable. + Consequently, it is suggested that "re:" and one of the variations of + the tokens for a forward supported by the base subject extraction + rules be adopted for Internet mail messages, since doing so makes it + a simple display-time task to localize the token language for the + user. + +8. IANA Considerations + + [IMAP] capabilities are registered by publishing a standards track or + IESG-approved experimental RFC. This document constitutes + registration of the SORT and THREAD capabilities in the [IMAP] + capabilities registry. + + + + + + + +Crispin & Murchison Standards Track [Page 16] + +RFC 5256 IMAP Sort June 2008 + + + This document creates a new [IMAP] threading algorithms registry, + which registers threading algorithms by publishing a standards track + or IESG-approved experimental RFC. This document constitutes + registration of the ORDEREDSUBJECT and REFERENCES algorithms in that + registry. + +9. Normative References + + [ABNF] Crocker, D., Ed., and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", STD 68, RFC 5234, January + 2008. + + [CHARSET] Freed, N. and J. Postel, "IANA Charset Registration + Procedures", BCP 19, RFC 2978, October 2000. + + [IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - + VERSION 4rev1", RFC 3501, March 2003. + + [IMAP-I18N] Newman, C., Gulbrandsen, A., and A. Melnikov, "Internet + Message Access Protocol Internationalization", RFC + 5255, June 2008. + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2822] Resnick, P., Ed., "Internet Message Format", RFC 2822, + April 2001. + + [UNICASEMAP] Crispin, M., "i;unicode-casemap - Simple Unicode + Collation Algorithm", RFC 5051, October 2007. + + [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO + 10646", STD 63, RFC 3629, November 2003. + +10. Informative References + + [IMAP-MODELS] Crispin, M., "Distributed Electronic Mail Models in + IMAP4", RFC 1733, December 1994. + + [THREADING] Zawinski, J. "Message Threading", + http://www.jwz.org/doc/threading.html, 1997-2002. + + + + + + + + + + +Crispin & Murchison Standards Track [Page 17] + +RFC 5256 IMAP Sort June 2008 + + +Authors' Addresses + + Mark R. Crispin + Panda Programming + 6158 NE Lariat Loop + Bainbridge Island, WA 98110-2098 + + Phone: +1 (206) 842-2385 + EMail: IMAP+SORT+THREAD@Lingling.Panda.COM + + + Kenneth Murchison + Carnegie Mellon University + 5000 Forbes Avenue + Cyert Hall 285 + Pittsburgh, PA 15213 + + Phone: +1 (412) 268-2638 + EMail: murch@andrew.cmu.edu + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Crispin & Murchison Standards Track [Page 18] + +RFC 5256 IMAP Sort June 2008 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2008). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Crispin & Murchison Standards Track [Page 19] + diff --git a/imap/docs/rfc/rfc5257.txt b/imap/docs/rfc/rfc5257.txt new file mode 100644 index 00000000..1d088e59 --- /dev/null +++ b/imap/docs/rfc/rfc5257.txt @@ -0,0 +1,1739 @@ + + + + + + +Network Working Group C. Daboo +Request for Comments: 5257 Apple Inc. +Category: Experimental R. Gellens + QUALCOMM Incorporated + June 2008 + + + Internet Message Access Protocol - ANNOTATE Extension + +Status of This Memo + + This memo defines an Experimental Protocol for the Internet + community. It does not specify an Internet standard of any kind. + Discussion and suggestions for improvement are requested. + Distribution of this memo is unlimited. + +Abstract + + The ANNOTATE extension to the Internet Message Access Protocol + permits clients and servers to maintain "meta data" for messages, or + individual message parts, stored in a mailbox on the server. For + example, this can be used to attach comments and other useful + information to a message. It is also possible to attach annotations + to specific parts of a message, so that, for example, they could be + marked as seen, or important, or a comment added. + + Note that this document was the product of a WG that had good + consensus on how to approach the problem. Nevertheless, the WG felt + it did not have enough information on implementation and deployment + hurdles to meet all of the requirements of a Proposed Standard. The + IETF solicits implementations and implementation reports in order to + make further progress. + + Implementers should be aware that this specification may change in an + incompatible manner when going to Proposed Standard status. However, + any incompatible changes will result in a new capability name being + used to prevent problems with any deployments of the experimental + extension. + + + + + + + + + + + + + +Daboo & Gellens Experimental [Page 1] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +Table of Contents + + 1. Introduction and Overview .......................................3 + 2. Conventions Used in This Document ...............................4 + 3. Data Model ......................................................4 + 3.1. Overview ...................................................4 + 3.2. Namespace of Entries and Attributes ........................4 + 3.2.1. Entry Names .........................................5 + 3.2.2. Attribute Names .....................................7 + 3.3. Private Versus Shared ......................................7 + 3.4. Access Control .............................................8 + 3.5. Access to Standard IMAP Flags and Keywords ................11 + 4. IMAP Protocol Changes ..........................................11 + 4.1. General Considerations ....................................11 + 4.2. ANNOTATE Parameter with the SELECT/EXAMINE Commands .......12 + 4.3. ANNOTATION Message Data Item in FETCH Command .............12 + 4.4. ANNOTATION Message Data Item in FETCH Response ............14 + 4.5. ANNOTATION Message Data Item in STORE .....................16 + 4.6. ANNOTATION Interaction with COPY ..........................18 + 4.7. ANNOTATION Message Data Item in APPEND ....................18 + 4.8. ANNOTATION Criterion in SEARCH ............................19 + 4.9. ANNOTATION Key in SORT ....................................20 + 4.10. New ACL Rights ...........................................21 + 5. Formal Syntax ..................................................21 + 6. IANA Considerations ............................................23 + 6.1. Entry and Attribute Registration Template .................23 + 6.2. Entry Registrations .......................................24 + 6.2.1. /comment ...........................................24 + 6.2.2. /flags .............................................24 + 6.2.3. /altsubject ........................................25 + 6.2.4. /<section-part>/comment ............................25 + 6.2.5. /<section-part>/flags/seen .........................26 + 6.2.6. /<section-part>/flags/answered .....................26 + 6.2.7. /<section-part>/flags/flagged ......................27 + 6.2.8. /<section-part>/flags/forwarded ....................27 + 6.3. Attribute Registrations ...................................28 + 6.3.1. value ..............................................28 + 6.3.2. size ...............................................28 + 6.4. Capability Registration ...................................28 + 7. Internationalization Considerations ............................29 + 8. Security Considerations ........................................29 + 9. References .....................................................29 + 9.1. Normative References ......................................29 + 9.2. Informative References ....................................30 + 10. Acknowledgments ...............................................30 + + + + + + +Daboo & Gellens Experimental [Page 2] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +1. Introduction and Overview + + The ANNOTATE extension is present in any IMAP [RFC3501] + implementation that returns "ANNOTATE-EXPERIMENT-1" as one of the + supported capabilities in the CAPABILITY response. + + This extension makes the following changes to the IMAP protocol: + + a. adds a new ANNOTATION message data item for use in FETCH. + + b. adds a new ANNOTATION message data item for use in STORE. + + c. adds a new ANNOTATION search criterion for use in SEARCH. + + d. adds a new ANNOTATION sort key for use in the SORT extension. + + e. adds a new ANNOTATION data item for use in APPEND. + + f. adds a new requirement on the COPY command. + + g. adds a new ANNOTATE parameter for use with the SELECT/EXAMINE + commands. + + h. adds two new response codes to indicate store failures of + annotations. + + i. adds a new untagged response code for the SELECT or EXAMINE + commands to indicate the maximum sized annotation that can be + stored. + + j. adds a new Access Control List (ACL) "bit" for use with the ACL + extensions [RFC2086] and [RFC4314]. + + The data model used for the storage of annotations is based on the + Application Configuration Access Protocol [RFC2244]. Note that there + is no inheritance in annotations. + + If a server supports annotations, then it MUST store all annotation + data permanently, i.e., there is no concept of "session only" + annotations that would correspond to the behavior of "session" flags + as defined in the IMAP base specification. + + In order to provide optimum support for a disconnected client (one + that needs to synchronize annotations for use when offline), servers + SHOULD also support the Conditional STORE [RFC4551] extension. + + The rest of this document describes the data model and protocol + changes more rigorously. + + + +Daboo & Gellens Experimental [Page 3] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +2. Conventions Used in This Document + + The examples in this document use "C:" and "S:" to indicate lines + sent by the client and server, respectively. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + +3. Data Model + +3.1. Overview + + The data model for annotations in ANNOTATE uses a uniquely named + entry that contains a set of standard attributes. Thus, a single + coherent unit of "meta data" for a message is stored as a single + entry, made up of several attributes. + + For example, a comment annotation added to a message has an entry + name of "/comment". This entry is composed of several attributes + such as "value", "size", etc., that contain the properties and data + of the entry. + + The protocol changes to IMAP, described below, allow a client to + access or change the values of any attribute in any entry in a + message annotation, assuming it has sufficient access rights to do so + (see Section 3.4 for specifics). + +3.2. Namespace of Entries and Attributes + + A message may contain zero or more annotations, each of which is a + single uniquely named entry. Each entry has a hierarchical name, + with each component of the name separated by a slash ("/"). An entry + name MUST NOT contain two consecutive "/" characters and MUST NOT end + with a "/" character. + + Each entry is made up of a set of attributes. Each attribute has a + hierarchical name, with each component of the name separated by a + period ("."). An attribute name MUST NOT contain two consecutive "." + characters and MUST NOT end with a "." character. + + The value of an attribute is "NIL" (has no value), or is a string of + zero or more octets. + + Entry and attribute names MUST NOT contain asterisk ("*") or percent + ("%") characters, and MUST NOT contain non-ASCII characters or the + NULL octet. Invalid entry or attribute names result in a BAD + response in any IMAP commands where they are used. + + + +Daboo & Gellens Experimental [Page 4] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + Attribute names MUST NOT contain any hierarchical components with the + names "priv" or "shared", as those have special meaning (see Section + 3.3). + + Entry and attribute names are case-sensitive. + + Use of control or punctuation characters in entry and attribute names + is strongly discouraged. + + This specification defines an initial set of entry and attribute + names available for use in message annotations. In addition, an + extension mechanism is described to allow additional names to be + added as needed. + +3.2.1. Entry Names + + Entry names MUST be specified in a standards track or IESG approved + experimental RFC, or fall under the vendor namespace. See Section + 6.1 for the registration template. + + / + Defines the top-level of entries associated with an entire + message. This entry itself does not contain any attributes. All + entries that start with a numeric character ("0" - "9") refer to + an annotation on a specific body part. All other entries are for + annotations on the entire message. + + /comment + Defines a comment or note associated with an entire message. + + /flags + This entry hierarchy is reserved for future use. + + /altsubject + Contains text supplied by the message recipient to be used by the + client, instead of the original message Subject. + + /vendor/<vendor-token> + Defines the top-level of entries associated with an entire message + as created by a particular product of some vendor. These sub- + entries can be used by vendors to provide client-specific + annotations. The vendor-token MUST be registered with IANA, using + the [RFC2244] vendor subtree registry. + + /<section-part> + Defines the top-level of entries associated with a specific body + part of a message. This entry itself does not contain any + attributes. The section-part is a numeric part specifier. Its + + + +Daboo & Gellens Experimental [Page 5] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + syntax is the same as the section-part ABNF element defined in + [RFC3501]. The server MUST return a BAD response if the client + uses an incorrect part specifier (either incorrect syntax or a + specifier referring to a non-existent part). The server MUST + return a BAD response if the client uses an empty part specifier + (which is used in IMAP to represent the entire message). + + /<section-part>/comment + Defines a comment or note associated with a specific body part of + a message. + + /<section-part>/flags + Defines the top-level of entries associated with the flag state + for a specific body part of a message. All sub-entries are + maintained entirely by the client. There is no implicit change to + any flag by the server. + + /<section-part>/flags/seen + This is similar to the IMAP \Seen flag, except it applies + to only the body part referenced by the entry. + + /<section-part>/flags/answered + This is similar to the IMAP \Answered flag, except it + applies to only the body part referenced by the entry. + + /<section-part>/flags/flagged + This is similar to the IMAP \Flagged flag, except it + applies to only the body part referenced by the entry. + + /<section-part>/flags/forwarded + This is similar to the IMAP $Forwarded keyword, except it + applies to only the body part referenced by the entry. + + Defines flags for a specific body part of a message. The "value" + attribute of each of the entries described above must be either + "1", "0", or "NIL". "1" corresponds to the flag being set. + + /<section-part>/vendor/<vendor-token> + Defines the top-level of entries associated with a specific body + part of a message as created by a particular product of some + vendor. This entry can be used by vendors to provide client + specific annotations. The vendor-token MUST be registered with + IANA. + + + + + + + + +Daboo & Gellens Experimental [Page 6] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +3.2.2. Attribute Names + + Attribute names MUST be specified in a standards track or IESG + approved experimental RFC. See Section 6.1 for the registration + template. + + All attribute names implicitly have a ".priv" and a ".shared" suffix + that maps to private and shared versions of the entry. Searching or + fetching without using either suffix will include both. The client + MUST specify either a ".priv" or ".shared" suffix when storing an + annotation or sorting on annotations. + + value + A string or binary data representing the value of the annotation. + To delete an annotation, the client can store "NIL" into the + value. If the client requests the value attribute for a non- + existent entry, then the server MUST return "NIL" for the value. + The content represented by the string is determined by the + content-type used to register the entry (see Section 6.1 for entry + registration templates). Where applicable, the registered + content-type MUST include a charset parameter. Text values SHOULD + use the utf-8 [RFC3629] character set. Note that binary data + (data which may contain the NULL octet) is allowed (e.g., for + storing images), and this extension uses the "literal8" syntax + element [RFC4466] to allow such data to be written to or read from + the server. + + size + The size of the value, in octets. Set automatically by the + server, read-only to clients. If the client requests the size + attribute for a non-existent entry, then the server MUST return + "0" (zero) for the size. + +3.3. Private Versus Shared + + Some IMAP mailboxes are private, accessible only to the owning user. + Other mailboxes are not, either because the owner has set an ACL + [RFC4314] that permits access by other users, or because it is a + shared mailbox. + + This raises the issue of shared versus private annotations. + + If all annotations are private, it is then impossible to have + annotations in a shared or otherwise non-private mailbox be visible + to other users. This eliminates what could be a useful aspect of + annotations in a shared environment. An example of such use is a + shared IMAP folder containing bug reports. Engineers may want to use + + + + +Daboo & Gellens Experimental [Page 7] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + annotations to add information to existing messages, indicate + assignments, status, etc. This use requires shared annotations. + + If all annotations are shared, it is impossible to use annotations + for private notes on messages in shared mailboxes. Also, modifying + an ACL to permit access to a mailbox by other users may + unintentionally expose private information. + + There are also situations in which both shared and private + annotations are useful. For example, an administrator may want to + set shared annotations on messages in a shared folder, which + individual users may wish to supplement with additional notes. + + If shared and private annotations are to coexist, we need a clear way + to differentiate them. Also, it should be as easy as possible for a + client to access both and not overlook either. There is also a + danger in allowing a client to store an annotation without knowing if + it is shared or private. + + This document proposes two standard suffixes for all attributes: + ".shared" and ".priv". A SEARCH or FETCH command that specifies + neither, uses both. STORE, APPEND, and SORT commands MUST explicitly + use ".priv" or ".shared" suffixes. + + If the ANNOTATE extension is present, support for shared annotations + in servers is REQUIRED, while support for private annotations in + servers is OPTIONAL. This recognizes the fact that support for + private annotations may introduce a significant increase in + complexity to a server in terms of tracking ownership of the + annotations, how quota is determined for users based on their own + annotations, etc. Clients that support the ANNOTATE extension MUST + handle both shared and private annotations. + +3.4. Access Control + + A user needs to have appropriate rights in order to read or write + ".priv" or ".shared" annotation values. How those rights are + calculated depends on whether or not the ACL [RFC2086] extension or + its update [RFC4314] is present. If a client attempts to store or + fetch an annotation to which they do not have the appropriate rights, + the server MUST respond with a NO response. + + When the ACL extension is not present, access to annotation values is + governed by the nature of the selected state, in particular whether + the mailbox was SELECTED or EXAMINED in READ-ONLY or READ-WRITE mode. + + + + + + +Daboo & Gellens Experimental [Page 8] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + When the ACL extension is present, the server MUST recognize the new + ACL "n" right, in addition to the ones defined by the ACL extension + itself. + + For ".priv" annotation values, the "r" right controls both read and + write access. When it is on, access to ".priv" annotations is + allowed; when it is off, access to ".priv" annotations is disallowed. + + For ".shared" annotation values, the "r" right controls read access. + When it is on, ".shared" annotations can be read; when it is off, + ".shared" annotations cannot be read. + + For ".shared" annotation values, the "n" right controls write access. + When it is on, ".shared" annotations can be changed or created + through either a STORE or APPEND command; when it is off, ".shared" + annotations cannot be changed or created. The "n" right constitutes + a "shared flag right" as defined in Section 6.2 of [RFC4314]. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Daboo & Gellens Experimental [Page 9] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + A summary of all the access control restrictions is tabulated below + + +---------------+---------------+-----------------------------------+ + | Server Type | Action on | Type of mailbox | + | | annotation | | + +===============+===============+===================================+ + | | | | + | | read .priv | Any mailbox that can be SELECTED | + | | values | or EXAMINED. | + | | | | + | +---------------+-----------------------------------+ + | | | | + | | write .priv | Any SELECTED [READ-WRITE] mailbox.| + | | values | SELECTED [READ-ONLY] mailboxes MAY| + | Server | | also permit writes. | + | without | | | + | ACL Extension +---------------+-----------------------------------+ + | | | | + | | read .shared | Any mailbox that can be SELECTED | + | | values | or EXAMINED. | + | | | | + | +---------------+-----------------------------------+ + | | | | + | | write .shared | Any mailbox that can be SELECTED | + | | values | or EXAMINED and is [READ-WRITE]. | + | | | | + +---------------+---------------+-----------------------------------+ + | | | | + | | read .priv | Any mailbox with the "r" | + | | values | ACL right. | + | | | | + | +---------------+-----------------------------------+ + | | | | + | | write .priv | Any mailbox with the "r" | + | Server | values | ACL right. | + | with | | | + | ACL Extension +---------------+-----------------------------------+ + | | | | + | | read .shared | Any mailbox with the "r" | + | | values | ACL right. | + | | | | + | +---------------+-----------------------------------+ + | | | | + | | write .shared | Any mailbox with the "n" | + | | values | ACL right. | + | | | | + +---------------+---------------+-----------------------------------+ + + + + +Daboo & Gellens Experimental [Page 10] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +3.5. Access to Standard IMAP Flags and Keywords + + Due to the ambiguity of how private and shared values would map to + the base IMAP flag and keyword values, the ANNOTATE extension does + not expose IMAP flags or keywords as entries. However, the /flags + annotation entry is reserved for future use and MUST NOT be used by + clients or servers supporting this extension. + + Clients that need to implement shared and private "flags" can create + their own annotation entries for those, completely bypassing the base + IMAP flag/keyword behavior. + +4. IMAP Protocol Changes + +4.1. General Considerations + + Servers may be able to offer only a limited level of support for + annotations in mailboxes, and it is useful for clients to be able to + know what level of support is available. Servers MUST return an + ANNOTATIONS response code during the SELECT or EXAMINE command for a + mailbox to indicate the level of support. Possible data items used + with the ANNOTATIONS response code are: + + "NONE" - this indicates that the mailbox being selected does not + support annotations at all. Clients MUST NOT attempt to use + annotation extensions in commands for this mailbox. + + "READ-ONLY" - this indicates that the annotations supported by the + mailbox cannot be changed by the client. Clients MUST NOT attempt + to store annotations on any messages in a mailbox with this + response code. + + "NOPRIVATE" - this indicates that the server does not support + private annotations on the mailbox. Only shared annotations are + supported. Clients SHOULD only attempt to read or store + annotations attributes with the ".shared" suffix. If a client + uses an attribute with the ".priv" suffix in a FETCH command, then + servers should return the attribute value in the FETCH response as + "NIL". If a client uses an attribute with the ".priv" suffix in a + STORE command (or an APPEND command targeted at the mailbox), then + the server MUST return a NO response. + + numeric values - if servers support writable annotations, then the + server MUST indicate the maximum size in octets for an annotation + value by providing the maximum size value in the response code. + Clients MUST NOT store annotation values of a size greater than + the amount indicated by the server. Servers MUST accept a minimum + + + + +Daboo & Gellens Experimental [Page 11] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + annotation data size of at least 1024 octets if annotations can be + written. + + In addition, the server MAY limit the total number of annotations for + a single message. However, the server MUST provide a minimum + annotation count per message of at least 10. + +4.2. ANNOTATE Parameter with the SELECT/EXAMINE Commands + + The ANNOTATE extension defines a single optional SELECT parameter + [RFC4466] "ANNOTATE", which is used to turn on unsolicited responses + for annotations as described in Section 4.4. This optional parameter + results in a per-mailbox state change, i.e., it must be used in each + SELECT/EXAMINE command in order to be effective, irrespective of + whether it was used in a previous SELECT/EXAMINE during the same + session. + + Example: + + C: a SELECT INBOX (ANNOTATE) + S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen) + S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft + \Deleted \Seen \*)] + S: * 10268 EXISTS + S: * 1 RECENT + S: * OK [UNSEEN 10268] + S: * OK [UIDVALIDITY 890061587] + S: * OK [UIDNEXT 34643] + S: * OK [ANNOTATIONS 20480 NOPRIVATE] + S: a OK [READ-WRITE] Completed + + In the above example, a SELECT command with the ANNOTATE parameter + is issued. The response from the server includes the required + ANNOTATIONS response that indicates that the server supports + annotations up to a maximum size of 20480 octets, and does not + support private annotations (only shared). + +4.3. ANNOTATION Message Data Item in FETCH Command + + This extension adds an ANNOTATION message data item to the FETCH + command. This allows clients to retrieve annotations for a range of + messages in the currently selected mailbox. + + ANNOTATION <entry-specifier> <attribute-specifier> + + The ANNOTATION message data item, when used by the client in the + FETCH command, takes an entry specifier and an attribute + specifier. + + + +Daboo & Gellens Experimental [Page 12] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + Example: + + C: a FETCH 1 (ANNOTATION (/comment value)) + S: * 1 FETCH (ANNOTATION (/comment + (value.priv "My comment" + value.shared "Group note"))) + S: a OK Fetch complete + + In the above example, the content of the "value" attribute for the + "/comment" entry is requested by the client and returned by the + server. Since neither ".shared" nor ".priv" was specified, both + are returned. + + "*" and "%" wild card characters can be used in entry specifiers to + match one or more characters at that position, with the exception + that "%" does not match the "/" hierarchy delimiter. Thus, an entry + specifier of "/%" matches entries such as "/comment" and + "/altsubject", but not "/1/comment". + + Example: + + C: a UID FETCH 1123 (UID ANNOTATION + (/* (value.priv size.priv))) + S: * 12 FETCH (UID 1123 ANNOTATION + (/comment (value.priv "My comment" + size.priv "10") + /altsubject (value.priv "Rhinoceroses!" + size.priv "13") + /vendor/foobar/label.priv + (value.priv "label43" + size.priv "7") + /vendor/foobar/personality + (value.priv "Tallulah Bankhead" + size.priv "17"))) + S: a OK Fetch complete + + In the above example, the contents of the private "value" and + "size" attributes for any entries in the "/" hierarchy are + requested by the client and returned by the server. + + + + + + + + + + + + +Daboo & Gellens Experimental [Page 13] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + Example: + + C: a FETCH 1 (ANNOTATION (/% value.shared)) + S: * 1 FETCH (ANNOTATION + (/comment (value.shared "Patch Mangler") + /altsubject (value.shared "Patches? We don't + need no steenkin patches!"))) + S: a OK Fetch complete + + In the above example, the contents of the shared "value" + attributes for entries at the top level only of the "/" hierarchy + are requested by the client and returned by the server. + + Entry and attribute specifiers can be lists of atomic specifiers, so + that multiple items of each type may be returned in a single FETCH + command. + + Example: + + C: a FETCH 1 (ANNOTATION + ((/comment /altsubject) value.priv)) + S: * 1 FETCH (ANNOTATION + (/comment (value.priv "What a chowder-head") + /altsubject (value.priv "How to crush beer cans"))) + S: a OK Fetch complete + + In the above example, the contents of the private "value" + attributes for the two entries "/comment" and "/altsubject" are + requested by the client and returned by the server. + +4.4. ANNOTATION Message Data Item in FETCH Response + + The ANNOTATION message data item in the FETCH response displays + information about annotations in a message. + + ANNOTATION parenthesized list + + The response consists of a list of entries, each of which have a + list of attribute-value pairs. + + + + + + + + + + + + +Daboo & Gellens Experimental [Page 14] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + Example: + + C: a FETCH 1 (ANNOTATION (/comment value)) + S: * 1 FETCH (ANNOTATION (/comment + (value.priv "My comment" + value.shared NIL))) + S: a OK Fetch complete + + In the above example, a single entry with a single attribute-value + pair is returned by the server. Since the client did not specify + a ".shared" or ".priv" suffix, both are returned. Only the + private attribute has a value (the shared value is "NIL"). + + Example: + + C: a FETCH 1 (ANNOTATION + ((/comment /altsubject) value)) + S: * 1 FETCH (ANNOTATION + (/comment (value.priv "My comment" + value.shared NIL) + /altsubject (value.priv "My subject" + value.shared NIL))) + S: a OK Fetch complete + + In the above example, two entries, each with a single attribute- + value pair, are returned by the server. Since the client did not + specify a ".shared" or ".priv" suffix, both are returned. Only + the private attributes have values; the shared attributes are + "NIL". + + Example: + + C: a FETCH 1 (ANNOTATION + (/comment (value size))) + S: * 1 FETCH (ANNOTATION + (/comment + (value.priv "My comment" + value.shared NIL + size.priv "10" + size.shared "0"))) + S: a OK Fetch complete + + In the above example, a single entry with two attribute-value + pairs is returned by the server. Since the client did not specify + a ".shared" or ".priv" suffix, both are returned. Only the + private attributes have values; the shared attributes are "NIL". + + + + + +Daboo & Gellens Experimental [Page 15] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + Servers SHOULD send ANNOTATION message data items in unsolicited + FETCH responses if an annotation entry is changed by a third-party, + and the ANNOTATE select parameter was used. This allows servers to + keep clients updated with changes to annotations by other clients. + + Unsolicited ANNOTATION responses MUST NOT include ANNOTATION data + values -- only the entry name of the ANNOTATION that has changed. + This restriction avoids sending ANNOTATION data values (which may be + large) to a client unless the client explicitly asks for the value. + + Example: + + C: a STORE 1 +FLAGS (\Seen) + S: * 1 FETCH (FLAGS (\Seen)) + ANNOTATION (/comment)) + S: a OK STORE complete + + In the above example, an unsolicited ANNOTATION response is + returned during a STORE command. The unsolicited response + contains only the entry name of the annotation that changed, and + not its value. + +4.5. ANNOTATION Message Data Item in STORE + + ANNOTATION <parenthesized entry-attribute-value list> + + Sets the specified list of entries by adding or replacing the + specified attributes with the values provided. Clients can use + "NIL" for values of attributes it wants to remove from entries. + + The ANNOTATION message data item used with the STORE command has an + implicit ".SILENT" behavior. This means the server does not generate + an untagged FETCH in response to the STORE command and assumes that + the client updates its own cache if the command succeeds. Though + note, that if the Conditional STORE extension [RFC4551] is present, + then an untagged FETCH response with a MODSEQ data item will be + returned by the server as required by [RFC4551]. + + If the server is unable to store an annotation because the size of + its value is too large, the server MUST return a tagged NO response + with a "[ANNOTATE TOOBIG]" response code. + + If the server is unable to store a new annotation because the maximum + number of allowed annotations has already been reached, the server + MUST return a tagged NO response with a "[ANNOTATE TOOMANY]" response + code. + + + + + +Daboo & Gellens Experimental [Page 16] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + Example: + + C: a STORE 1 ANNOTATION (/comment + (value.priv "My new comment")) + S: a OK Store complete + + In the above example, the entry "/comment" is created (if not + already present). Its private attribute "value" is created if not + already present, or replaced if it exists. "value.priv" is set to + "My new comment". + + Example: + + C: a STORE 1 ANNOTATION (/comment + (value.shared NIL)) + S: a OK Store complete + + In the above example, the shared "value" attribute of the entry + "/comment" is removed by storing "NIL" into the attribute. + + Multiple entries can be set in a single STORE command by listing + entry-attribute-value pairs in the list. + + Example: + + C: a STORE 1 ANNOTATION (/comment + (value.priv "Get tix Tuesday") + /altsubject + (value.priv "Wots On")) + S: a OK Store complete + + In the above example, the entries "/comment" and "/altsubject" are + created (if not already present) and the private attribute "value" + is created or replaced for each entry. + + Multiple attributes can be set in a single STORE command by listing + multiple attribute-value pairs in the entry list. + + + + + + + + + + + + + + +Daboo & Gellens Experimental [Page 17] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + Example: + + C: a STORE 1 ANNOTATION (/comment + (value.priv "My new comment" + value.shared "foo's bar")) + S: a OK Store complete + + In the above example, the entry "/comment" is created (if not + already present) and the private and shared "value" attributes are + created if not already present, or replaced if they exist. + +4.6. ANNOTATION Interaction with COPY + + The COPY command can be used to move messages from one mailbox to + another on the same server. Servers that support the ANNOTATION + extension MUST, for each message being copied, copy all ".priv" + annotation data for the current user only, and all ".shared" + annotation data along with the message to the new mailbox. The only + exceptions to this are if the destination mailbox permissions are + such that either the ".priv" or ".shared" annotations are not + allowed, or if the destination mailbox is of a type that does not + support annotations or does not support storing of annotations (a + mailbox that returns a "NONE" or "READ-ONLY" response code in its + ANNOTATIONS response), or if the destination mailbox cannot support + the size of an annotation because it exceeds the ANNOTATIONS value. + Servers MUST NOT copy ".priv" annotation data for users other than + the current user. + +4.7. ANNOTATION Message Data Item in APPEND + + ANNOTATION <parenthesized entry-attribute-value list> + + Sets the specified list of entries and attributes in the resulting + message. + + The APPEND command can include annotations for the message being + appended via the addition of a new append data item [RFC4466]. The + new data item can also be used with the multi-append [RFC3502] + extension that allows multiple messages to be appended via a single + APPEND command. + + + + + + + + + + + +Daboo & Gellens Experimental [Page 18] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + Example: + + C: a APPEND drafts ANNOTATION (/comment + (value.priv "Don't send until I say so")) {310} + S: + Ready for literal data + C: MIME-Version: 1.0 + ... + C: + S: a OK APPEND completed + + In the above example, a comment with a private value is added to a + new message appended to the mailbox. The ellipsis represents the + bulk of the message. + +4.8. ANNOTATION Criterion in SEARCH + + ANNOTATION <entry-name> <attribute-name> <value> + + The ANNOTATION criterion for the SEARCH command allows a client to + search for a specified string in the value of an annotation entry of + a message. + + Messages that have annotations with entries matching <entry-name>, + attributes matching <attribute-name>, and the specified string + <value> in their values are returned in the SEARCH results. The "*" + character can be used in the entry name field to match any content in + those items. The "%" character can be used in the entry name field + to match a single level of hierarchy only. + + Only the "value", "value.priv", and "value.shared" attributes can be + searched. Clients MUST NOT specify an attribute other than either + "value", "value.priv", or "value.shared". Servers MUST return a BAD + response if the client tries to search any other attribute. + + Example: + + C: a SEARCH ANNOTATION /comment value "IMAP4" + S: * SEARCH 2 3 5 7 11 13 17 19 23 + S: a OK Search complete + + In the above example, the message numbers of any messages + containing the string "IMAP4" in the shared or private "value" + attribute of the "/comment" entry are returned in the search + results. + + + + + + + +Daboo & Gellens Experimental [Page 19] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + Example: + + C: a SEARCH ANNOTATION * value.priv "IMAP4" + S: * SEARCH 1 2 3 5 8 13 21 34 + S: a OK Search complete + + In the above example, the message numbers of any messages + containing the string "IMAP4" in the private "value" attribute of + any entry are returned in the search results. + +4.9. ANNOTATION Key in SORT + + ANNOTATION <entry-name> <attribute-name> + + The ANNOTATION criterion for the SORT command [RFC5256] instructs the + server to return the sequence numbers or Unique Identifiers (UIDs) of + messages in a mailbox, sorted using the values of the specified + annotations. The ANNOTATION criterion is available if the server + returns both ANNOTATE-EXPERIMENT-1 and SORT as supported capabilities + in the CAPABILITY command response. + + Messages are sorted using the values of the <attribute-name> + attributes in the <entry-name> entries. + + Clients MUST provide either the ".priv" or ".shared" suffix to the + attribute name to ensure that the server knows which specific value + to sort on. + + Only the "value.priv" and "value.shared" attributes can be used for + sorting. Clients MUST NOT specify an attribute other than either + "value.priv" or "value.shared". Servers MUST return a BAD response + if the client tries to sort on any other attribute. + + When either "value.priv" or "value.shared" is being sorted, the + server MUST use the character set value specified in the SORT command + to determine the appropriate sort order. + + Example: + + C: a SORT (ANNOTATION /altsubject value.shared) UTF-8 ALL + S: * SORT 2 3 4 5 1 11 10 6 7 9 8 + S: a OK Sort complete + + In the above example, the message numbers of all messages are + returned, sorted according to the shared "value" attribute of the + "/altsubject" entry. + + + + + +Daboo & Gellens Experimental [Page 20] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + Note that the ANNOTATION sort key must include a fully specified + entry -- wild cards are not allowed. + +4.10. New ACL Rights + + As discussed in Section 3.4, this extension adds a new "n" right to + the list of rights provided by the ACL extensions [RFC2086] and + [RFC4314]. + +5. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [RFC5234]. + + Non-terminals referenced but not defined below are as defined by + [RFC3501] with the new definitions in [RFC4466] superseding those in + [RFC3501]. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper or lower case characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + ann-size = "NONE" / + (("READ-ONLY" / nz-number) + [SP "NOPRIVATE"]) + ; response codes indicating the level of + ; support for annotations in a mailbox + + append-ext =/ att-annotate + ; modifies [RFC3501] extension behaviour + + att-annotate = "ANNOTATION" SP + "(" entry-att *(SP entry-att) ")" + + att-search = "value" / "value.priv" / "value.shared" + ; the only attributes that can be searched + + att-sort = "value.priv" / "value.shared" + ; the only attributes that can be sorted + + att-value = attrib SP value + + attrib = astring + ; dot-separated attribute name + ; MUST NOT contain "*" or "%" + + + + + +Daboo & Gellens Experimental [Page 21] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + attribs = attrib / "(" attrib *(SP attrib) ")" + ; one or more attribute specifiers + + capability =/ "ANNOTATE-EXPERIMENT-1" + ; defines the capability for this extension + + entries = entry-match / + "(" entry-match *(SP entry-match) ")" + + entry = astring + ; slash-separated path to entry + ; MUST NOT contain "*" or "%" + + entry-att = entry SP "(" att-value *(SP att-value) ")" + + entry-match = list-mailbox + ; slash-separated path to entry + ; MAY contain "*" or "%" for use as wild cards + + fetch-att =/ "ANNOTATION" SP "(" entries SP attribs ")" + ; modifies original IMAP fetch-att + + msg-att-dynamic =/ "ANNOTATION" SP + ( "(" entry-att *(SP entry-att) ")" / + "(" entry *(SP entry) ")" ) + ; extends FETCH response with annotation data + + resp-text-code =/ "ANNOTATE" SP "TOOBIG" / + "ANNOTATE" SP "TOOMANY" / + "ANNOTATIONS" SP ann-size + ; new response codes + + search-key =/ "ANNOTATION" SP entry-match SP att-search + SP value + ; modifies original IMAP search-key + + select-param =/ "ANNOTATE" + ; defines the select parameter used with + ; ANNOTATE extension + + sort-key =/ "ANNOTATION" SP entry SP att-sort + ; modifies original sort-key + + store-att-flags =/ att-annotate + ; modifies original IMAP STORE command + + value = nstring / literal8 + + + + +Daboo & Gellens Experimental [Page 22] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +6. IANA Considerations + + Entry names MUST be specified in a standards track or IESG approved + experimental RFC, or fall under the vendor namespace. Vendor names + MUST be registered. + + Attribute names MUST be specified in a standards track or IESG + approved experimental RFC. + + Each entry registration MUST include a content-type that is used to + indicate the nature of the annotation value. Where applicable, a + charset parameter MUST be included with the content-type. + +6.1. Entry and Attribute Registration Template + + To: iana@iana.org + Subject: IMAP Annotate Registration + + Please register the following IMAP Annotate item: + + [] Entry [] Attribute + + Name: ______________________________ + + Description: _______________________ + + ____________________________________ + + ____________________________________ + + Content-Type:_______________________ + + Contact person: ____________________ + + email: ____________________ + + + + + + + + + + + + + + + + +Daboo & Gellens Experimental [Page 23] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +6.2. Entry Registrations + + The following templates specify the IANA registrations of annotation + entries specified in this document. + +6.2.1. /comment + + To: iana@iana.org + Subject: IMAP Annotate Registration + + Please register the following IMAP Annotate item: + + [X] Entry [] Attribute + + Name: /comment + + Description: Defined in IMAP ANNOTATE extension document. + + Content-Type: text/plain; charset=utf-8 + + Contact person: Cyrus Daboo + + email: cyrus@daboo.name + +6.2.2. /flags + + To: iana@iana.org + Subject: IMAP Annotate Registration + + Please register the following IMAP Annotate item: + + [X] Entry [] Attribute + + Name: /flags + + Description: Reserved entry hierarchy. + + Content-Type: - + + Contact person: Cyrus Daboo + + email: cyrus@daboo.name + + + + + + + + + +Daboo & Gellens Experimental [Page 24] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +6.2.3. /altsubject + + To: iana@iana.org + Subject: IMAP Annotate Registration + + Please register the following IMAP Annotate item: + + [X] Entry [] Attribute + + Name: /altsubject + + Description: Defined in IMAP ANNOTATE extension document. + + Content-Type: text/plain; charset=utf-8 + + Contact person: Cyrus Daboo + + email: cyrus@daboo.name + +6.2.4. /<section-part>/comment + + To: iana@iana.org + Subject: IMAP Annotate Registration + + Please register the following IMAP Annotate item: + + [X] Entry [] Attribute + + Name: /<section-part>/comment + + Description: Defined in IMAP ANNOTATE extension document. + + Content-Type: text/plain; charset=utf-8 + + Contact person: Cyrus Daboo + + email: cyrus@daboo.name + + + + + + + + + + + + + + +Daboo & Gellens Experimental [Page 25] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +6.2.5. /<section-part>/flags/seen + + To: iana@iana.org + Subject: IMAP Annotate Registration + + Please register the following IMAP Annotate item: + + [X] Entry [] Attribute + + Name: /<section-part>/flags/seen + + Description: Defined in IMAP ANNOTATE extension document. + + Content-Type: text/plain; charset=utf-8 + + Contact person: Cyrus Daboo + + email: cyrus@daboo.name + +6.2.6. /<section-part>/flags/answered + + To: iana@iana.org + Subject: IMAP Annotate Registration + + Please register the following IMAP Annotate item: + + [X] Entry [] Attribute + + Name: /<section-part>/flags/answered + + Description: Defined in IMAP ANNOTATE extension document. + + Content-Type: text/plain; charset=utf-8 + + Contact person: Cyrus Daboo + + email: cyrus@daboo.name + + + + + + + + + + + + + + +Daboo & Gellens Experimental [Page 26] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +6.2.7. /<section-part>/flags/flagged + + To: iana@iana.org + Subject: IMAP Annotate Registration + + Please register the following IMAP Annotate item: + + [X] Entry [] Attribute + + Name: /<section-part>/flags/flagged + + Description: Defined in IMAP ANNOTATE extension document. + + Content-Type: text/plain; charset=utf-8 + + Contact person: Cyrus Daboo + + email: cyrus@daboo.name + +6.2.8. /<section-part>/flags/forwarded + + To: iana@iana.org + Subject: IMAP Annotate Registration + + Please register the following IMAP Annotate item: + + [X] Entry [] Attribute + + Name: /<section-part>/flags/forwarded + + Description: Defined in IMAP ANNOTATE extension document. + + Content-Type: text/plain; charset=utf-8 + + Contact person: Cyrus Daboo + + email: cyrus@daboo.name + + + + + + + + + + + + + + +Daboo & Gellens Experimental [Page 27] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +6.3. Attribute Registrations + + The following templates specify the IANA registrations of annotation + attributes specified in this document. + +6.3.1. value + + To: iana@iana.org + Subject: IMAP Annotate Registration + + Please register the following IMAP Annotate item: + + [] Entry [X] Attribute + + Name: value + + Description: Defined in IMAP ANNOTATE extension document. + + Contact person: Cyrus Daboo + + email: cyrus@daboo.name + +6.3.2. size + + To: iana@iana.org + Subject: IMAP Annotate Registration + + Please register the following IMAP Annotate item: + + [] Entry [X] Attribute + + Name: size + + Description: Defined in IMAP ANNOTATE extension document. + + Contact person: Cyrus Daboo + + email: cyrus@daboo.name + +6.4. Capability Registration + + This document registers "ANNOTATE-EXPERIMENT-1" as an IMAPEXT + capability. + + + + + + + + +Daboo & Gellens Experimental [Page 28] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +7. Internationalization Considerations + + Annotations may contain values that include text strings, and both + searching and sorting are possible with annotations. Servers MUST + follow standard IMAP text normalization, character set conversion, + and collation rules when such operations are carried out, as would be + done for other textual fields being searched or sorted on. + +8. Security Considerations + + Annotations whose values are intended to remain private MUST be + stored in ".priv" values instead of ".shared" values, which may be + accessible to other users. + + Excluding the above issues, the ANNOTATE extension does not raise any + security considerations that are not present in the base IMAP + protocol; these issues are discussed in [RFC3501]. + +9. References + +9.1. Normative References + + [RFC2086] Myers, J., "IMAP4 ACL extension", RFC 2086, January 1997. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2244] Newman, C. and J. Myers, "ACAP -- Application + Configuration Access Protocol", RFC 2244, November 1997. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [RFC3502] Crispin, M., "Internet Message Access Protocol (IMAP) - + MULTIAPPEND Extension", RFC 3502, March 2003. + + [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO + 10646", STD 63, RFC 3629, November 2003. + + [RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL) Extension", + RFC 4314, December 2005. + + [RFC4466] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4 + ABNF", RFC 4466, April 2006. + + [RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", STD 68, RFC 5234, January + 2008. + + + +Daboo & Gellens Experimental [Page 29] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + + [RFC5256] Crispin, M. and K. Murchison, "Internet Message Access + Protocol - SORT and THREAD Extensions", RFC 5256, June + 2008. + +9.2. Informative References + + [RFC4551] Melnikov, A. and S. Hole, "IMAP Extension for Conditional + STORE Operation or Quick Flag Changes Resynchronization", + RFC 4551, June 2006. + +10. Acknowledgments + + Many thanks to Chris Newman for his detailed comments on the first + draft of this document, and to the participants at the ACAP working + dinner in Pittsburgh. The participants of the IMAPext working group + made significant contributions to this work. + +Authors' Addresses + + Cyrus Daboo + Apple Inc. + 1 Infinite Loop + Cupertino, CA 95014 + USA + + EMail: cyrus@daboo.name + URI: http://www.apple.com/ + + + Randall Gellens + QUALCOMM Incorporated + 5775 Morehouse Dr. + San Diego, CA 92121-2779 + USA + + EMail: randy@qualcomm.com + + + + + + + + + + + + + + + +Daboo & Gellens Experimental [Page 30] + +RFC 5257 IMAP ANNOTATE Extension June 2008 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2008). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Daboo & Gellens Experimental [Page 31] + diff --git a/imap/docs/rfc/rfc5258.txt b/imap/docs/rfc/rfc5258.txt new file mode 100644 index 00000000..a80ec156 --- /dev/null +++ b/imap/docs/rfc/rfc5258.txt @@ -0,0 +1,1739 @@ + + + + + + +Network Working Group B. Leiba +Request for Comments: 5258 IBM T.J. Watson Research Center +Obsoletes: 3348 A. Melnikov +Updates: 2193 Isode Limited +Category: Standards Track June 2008 + + + Internet Message Access Protocol version 4 - LIST Command Extensions + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + IMAP4 has two commands for listing mailboxes: LIST and LSUB. As we + have added extensions, such as Mailbox Referrals, that have required + specialized lists we have had to expand the number of list commands, + since each extension must add its function to both LIST and LSUB, and + these commands are not, as they are defined, extensible. If we've + needed the extensions to work together, we've had to add a set of + commands to mix the different options, the set increasing in size + with each new extension. This document describes an extension to the + base LIST command that will allow these additions to be done with + mutually compatible options to the LIST command, avoiding the + exponential increase in specialized list commands. + + + + + + + + + + + + + + + + + + + + + +Leiba & Melnikov Standards Track [Page 1] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + +Table of Contents + + 1. Introduction and Overview . . . . . . . . . . . . . . . . . . 3 + 2. Conventions Used in This Document . . . . . . . . . . . . . . 4 + 3. Extended LIST Command . . . . . . . . . . . . . . . . . . . . 4 + 3.1. Initial List of Selection Options . . . . . . . . . . . . 7 + 3.2. Initial List of Return Options . . . . . . . . . . . . . . 8 + 3.3. General Principles for Returning LIST Responses . . . . . 9 + 3.4. Additional Requirements on LIST-EXTENDED Clients . . . . . 9 + 3.5. CHILDINFO Extended Data Item . . . . . . . . . . . . . . . 10 + 4. The CHILDREN Return Option . . . . . . . . . . . . . . . . . . 11 + 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 + 6. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 19 + 7. Internationalization Considerations . . . . . . . . . . . . . 22 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 23 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 + 9.1. Guidelines for IANA . . . . . . . . . . . . . . . . . . . 23 + 9.2. Registration Procedure and Change Control . . . . . . . . 23 + 9.3. Registration Template for LIST-EXTENDED Options . . . . . 25 + 9.4. Initial LIST-EXTENDED Option Registrations . . . . . . . . 25 + 9.5. Registration Template for LIST-EXTENDED Extended Data + Item . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 + 9.6. Initial LIST-EXTENDED Extended Data Item Registrations . . 28 + 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29 + 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 + 11.1. Normative References . . . . . . . . . . . . . . . . . . . 29 + 11.2. Informative References . . . . . . . . . . . . . . . . . . 30 + + + + + + + + + + + + + + + + + + + + + + + + +Leiba & Melnikov Standards Track [Page 2] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + +1. Introduction and Overview + + The LIST command is extended by amending the syntax to allow options + and multiple patterns to be specified. The list of options replaces + the several commands that are currently used to mix and match the + information requested. The new syntax is backward compatible, with + no ambiguity: the new syntax is being used if one of the following + conditions is true: + + 1. if the first word after the command name begins with a + parenthesis ("LIST selection options") + + 2. if the second word after the command name begins with a + parenthesis ("multiple mailbox patterns") + + 3. if the LIST command has more than 2 parameters ("LIST return + options") + + Otherwise the original syntax is used. + + By adding options to the LIST command, we are announcing the intent + to phase out and eventually to deprecate the RLIST and RLSUB commands + described in [MBRef]. We are also defining the mechanism to request + extended mailbox information, such as is described in the Child + Mailbox Extension [CMbox]. The base LSUB command is not deprecated + by this extension; rather, this extension adds a way to obtain + subscription information with more options, with those server + implementations that support it. Clients that simply need a list of + subscribed mailboxes, as provided by the LSUB command, SHOULD + continue to use that command. + + This document defines an IMAP4 extension that is identified by the + capability string "LIST-EXTENDED". The LIST-EXTENDED extension makes + the following changes to the IMAP4 protocol, which are described in + more detail in Section 3 and Section 4: + + a. defines new syntax for LIST command options. + + b. extends LIST to allow for multiple mailbox patterns. + + c. adds LIST command selection options: SUBSCRIBED, REMOTE, and + RECURSIVEMATCH. + + d. adds LIST command return options: SUBSCRIBED and CHILDREN. + + e. adds new mailbox attributes: "\NonExistent", "\Subscribed", + "\Remote", "\HasChildren", and "\HasNoChildren". + + + + +Leiba & Melnikov Standards Track [Page 3] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + f. adds CHILDINFO extended data item. + +2. Conventions Used in This Document + + In examples, "C:" indicates lines sent by a client that is connected + to a server. "S:" indicates lines sent by the server to the client. + + The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" + are used in this document as specified in RFC 2119 [Kwds]. + + The term "canonical LIST pattern" refers to the canonical pattern + constructed internally by the server from the reference and mailbox + name arguments (Section 6.3.8 of [IMAP4]). The [IMAP4] LIST command + returns only mailboxes that match the canonical LIST pattern. + + Other terms are introduced where they are referenced for the first + time. + +3. Extended LIST Command + + This extension updates the syntax of the LIST command to allow for + multiple mailbox patterns to be specified, if they are enclosed in + parentheses. A mailbox name matches a list of mailbox patterns if it + matches at least one mailbox pattern. If a mailbox name matches + multiple mailbox patterns from the list, the server SHOULD return + only a single LIST response. + + Note that the non-extended LIST command is required to treat an empty + ("" string) mailbox name argument as a special request to return the + hierarchy delimiter and the root name of the name given in the + reference parameter (as per [IMAP4]). However, ANY extended LIST + command (extended in any of 3 ways specified in Section 1, or any + combination thereof) MUST NOT treat the empty mailbox name as such a + special request, and any regular processing described in this + document applies. In particular, if an extended LIST command has + multiple mailbox names and one (or more) of them is the empty string, + the empty string MUST be ignored for the purpose of matching. + + Some servers might restrict which patterns are allowed in a LIST + command. If a server doesn't accept a particular pattern, it MUST + silently ignore it. + + The LIST command syntax is also extended in two additional ways: by + adding a parenthesized list of command options between the command + name and the reference name (LIST selection options) and an optional + + + + + + +Leiba & Melnikov Standards Track [Page 4] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + list of options at the end that control what kind of information + should be returned (LIST return options). See the formal syntax in + Section 6 for specific details. + + A LIST selection option tells the server which mailbox names should + be selected by the LIST operation. The server should return + information about all mailbox names that match any of the "canonical + LIST pattern" (as described above) and satisfy additional selection + criteria (if any) specified by the LIST selection options. Let's + call any such mailbox name a "matched mailbox name". When multiple + selection options are specified, the server MUST return information + about mailbox names that satisfy every selection option, unless a + description of a particular specified option prescribes special + rules. An example of an option prescribing special rules is the + RECURSIVEMATCH selection option described later in this section. We + will use the term "selection criteria" when referring collectively to + all selection options specified in a LIST command. + + A LIST return option controls which information is returned for each + matched mailbox name. Note that return options MUST NOT cause the + server to report information about additional mailbox names. If the + client has not specified any return option, only information about + attributes should be returned by the server. (Of course, the server + is allowed to include any other information at will.) + + Both selection and return command options will be defined in this + document and in approved extension documents; each option will be + enabled by a capability string (one capability may enable multiple + options), and a client MUST NOT send an option for which the server + has not advertised support. A server MUST respond to options it does + not recognize with a BAD response. The client SHOULD NOT specify any + option more than once; however, if the client does this, the server + MUST act as if it received the option only once. The order in which + options are specified by the client is not significant. + + In general, each selection option except RECURSIVEMATCH will have a + corresponding return option. The REMOTE selection option is an + anomaly in this regard, and does not have a corresponding return + option. That is because it expands, rather than restricts, the set + of mailboxes that are returned. Future extensions to this + specification should keep parallelism in mind and define a pair of + corresponding options. + + This extension is identified by the capability string + "LIST-EXTENDED", and support for it is a prerequisite for any future + extensions that require specialized forms of the LIST command. Such + extensions MUST refer to this document and MUST add their function + through command options as described herein. Note that extensions + + + +Leiba & Melnikov Standards Track [Page 5] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + that don't require support for an extended LIST command, but use + extended LIST responses (see below), don't need to advertise the + "LIST-EXTENDED" capability string. + + This extension also defines extensions to the LIST response, allowing + a series of extended fields at the end, a parenthesized list of + tagged data (also referred to as "extended data item"). The first + element of an extended field is a tag, which identifies the type of + data. Tags MUST be registered with IANA, as described in Section 9.5 + of this document. An example of such an extended set might be + + tablecloth (("edge" "lacy") ("color" "red"))) (X-Sample "text")) + + or + + tablecloth ("edge" "lacy")) (X-Sample "text" "more text")) + + See the formal syntax, in Section 6, for the full syntactic details. + The server MUST NOT return any extended data item unless the client + has expressed its ability to support extended LIST responses, for + example, by using an extended LIST command. The server MAY return + data in the extended fields that was not directly solicited by the + client in the corresponding LIST command. For example, the client + can enable extra extended fields by using another IMAP extension that + make use of the extended LIST responses. The client MUST ignore all + extended fields it doesn't recognize. + + The LIST-EXTENDED capability also defines several new mailbox + attributes. + + The "\NonExistent" attribute indicates that a mailbox name does not + refer to an existing mailbox. Note that this attribute is not + meaningful by itself, as mailbox names that match the canonical LIST + pattern but don't exist must not be returned unless one of the two + conditions listed below is also satisfied: + + a. The mailbox name also satisfies the selection criteria (for + example, it is subscribed and the "SUBSCRIBED" selection option + has been specified). + + b. "RECURSIVEMATCH" has been specified, and the mailbox name has at + least one descendant mailbox name that does not match the LIST + pattern and does match the selection criteria. + + In practice, this means that the "\NonExistent" attribute is usually + returned with one or more of "\Subscribed", "\Remote", + "\HasChildren", or the CHILDINFO extended data item (see their + description below). + + + +Leiba & Melnikov Standards Track [Page 6] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + The "\NonExistent" attribute implies "\NoSelect". The "\NonExistent" + attribute MUST be supported and MUST be accurately computed. + +3.1. Initial List of Selection Options + + The selection options defined in this specification are as follows: + + SUBSCRIBED - causes the LIST command to list subscribed names, + rather than the existing mailboxes. This will often be a subset + of the actual mailboxes. It's also possible for this list to + contain the names of mailboxes that don't exist. In any case, the + list MUST include exactly those mailbox names that match the + canonical list pattern and are subscribed to. This option is + intended to supplement the LSUB command. Of particular note are + the mailbox attributes as returned by this option, compared with + what is returned by LSUB. With the latter, the attributes + returned may not reflect the actual attribute status on the + mailbox name, and the \NoSelect attribute has a second special + meaning (it indicates that this mailbox is not, itself, + subscribed, but that it has descendant mailboxes that are). With + the SUBSCRIBED selection option described here, the attributes are + accurate and complete, and have no special meanings. "LSUB" and + "LIST (SUBSCRIBED)" are, thus, not the same thing, and some + servers must do significant extra work to respond to "LIST + (SUBSCRIBED)". Because of this, clients SHOULD continue to use + "LSUB" unless they specifically want the additional information + offered by "LIST (SUBSCRIBED)". + + This option defines a new mailbox attribute, "\Subscribed", that + indicates that a mailbox name is subscribed to. The "\Subscribed" + attribute MUST be supported and MUST be accurately computed when + the SUBSCRIBED selection option is specified. + + Note that the SUBSCRIBED selection option implies the SUBSCRIBED + return option (see below). + + REMOTE - causes the LIST command to show remote mailboxes as well as + local ones, as described in [MBRef]. This option is intended to + replace the RLIST command and, in conjunction with the SUBSCRIBED + selection option, the RLSUB command. + + This option defines a new mailbox attribute, "\Remote", that + indicates that a mailbox is a remote mailbox. The "\Remote" + attribute MUST be accurately computed when the REMOTE option is + specified. + + The REMOTE selection option has no interaction with other options. + Its effect is to tell the server to apply the other options, if + + + +Leiba & Melnikov Standards Track [Page 7] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + any, to remote mailboxes, in addition to local ones. In + particular, it has no interaction with RECURSIVEMATCH (see below). + A request for (REMOTE RECURSIVEMATCH) is invalid, because a + request for (RECURSIVEMATCH) is. A request for (REMOTE + RECURSIVEMATCH SUBSCRIBED) is asking for all subscribed mailboxes, + both local and remote. + + RECURSIVEMATCH - this option forces the server to return information + about parent mailboxes that don't match other selection options, + but have some submailboxes that do. Information about children is + returned in the CHILDINFO extended data item, as described in + Section 3.5. + + Note 1: In order for a parent mailbox to be returned, it still has + to match the canonical LIST pattern. + + Note 2: When returning the CHILDINFO extended data item, it + doesn't matter whether or not the submailbox matches the canonical + LIST pattern. See also example 9 in Section 5. + + The RECURSIVEMATCH option MUST NOT occur as the only selection + option (or only with REMOTE), as it only makes sense when other + selection options are also used. The server MUST return BAD + tagged response in such case. + + Note that even if the RECURSIVEMATCH option is specified, the + client MUST still be able to handle a case when a CHILDINFO + extended data item is returned and there are no submailboxes that + meet the selection criteria of the subsequent LIST command, as + they can be deleted/renamed after the LIST response was sent, but + before the client had a chance to access them. + +3.2. Initial List of Return Options + + The return options defined in this specification are as follows: + + SUBSCRIBED - causes the LIST command to return subscription state + for all matching mailbox names. The "\Subscribed" attribute MUST + be supported and MUST be accurately computed when the SUBSCRIBED + return option is specified. Further, all mailbox flags MUST be + accurately computed (this differs from the behavior of the LSUB + command). + + CHILDREN - requests mailbox child information as originally proposed + in [CMbox]. See Section 4, below, for details. This option MUST + be supported by all servers. + + + + + +Leiba & Melnikov Standards Track [Page 8] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + +3.3. General Principles for Returning LIST Responses + + This section outlines several principles that can be used by server + implementations of this document to decide whether a LIST response + should be returned, as well as how many responses and what kind of + information they may contain. + + 1. At most one LIST response should be returned for each mailbox + name that matches the canonical LIST pattern. Server + implementors must not assume that clients will be able to + assemble mailbox attributes and other information returned in + multiple LIST responses. + + 2. There are only two reasons for including a matching mailbox name + in the responses to the LIST command (note that the server is + allowed to return unsolicited responses at any time, and such + responses are not governed by this rule): + + A. The mailbox name also satisfies the selection criteria. + + B. The mailbox name doesn't satisfy the selection criteria, but + it has at least one descendant mailbox name that satisfies + the selection criteria and that doesn't match the canonical + LIST pattern. + + For more information on this case, see the CHILDINFO extended + data item described in Section 3.5. Note that the CHILDINFO + extended data item can only be returned when the + RECURSIVEMATCH selection option is specified. + + 3. Attributes returned in the same LIST response must be treated + additively. For example, the following response + + S: * LIST (\Subscribed \NonExistent) "/" "Fruit/Peach" + + means that the "Fruit/Peach" mailbox doesn't exist, but it is + subscribed. + +3.4. Additional Requirements on LIST-EXTENDED Clients + + All clients that support this extension MUST treat an attribute with + a stronger meaning as implying any attribute that can be inferred + from it. For example, the client must treat the presence of the + \NoInferiors attribute as if the \HasNoChildren attribute was also + sent by the server. + + + + + + +Leiba & Melnikov Standards Track [Page 9] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + The following table summarizes inference rules described in + Section 3. + + +--------------------+-------------------+ + | returned attribute | implied attribute | + +--------------------+-------------------+ + | \NoInferiors | \HasNoChildren | + | \NonExistent | \NoSelect | + +--------------------+-------------------+ + +3.5. CHILDINFO Extended Data Item + + The CHILDINFO extended data item MUST NOT be returned unless the + client has specified the RECURSIVEMATCH selection option. + + The CHILDINFO extended data item in a LIST response describes the + selection criteria that has caused it to be returned and indicates + that the mailbox has at least one descendant mailbox that matches the + selection criteria. + + The LSUB command indicates this condition by using the "\NoSelect" + attribute, but the LIST (SUBSCRIBED) command MUST NOT do that, since + "\NoSelect" retains its original meaning here. Further, the + CHILDINFO extended data item is more general, in that it can be used + with any extended set of selection criteria. + + Note: Some servers allow for mailboxes to exist without requiring + their parent to exist. For example, a mailbox "Customers/ABC" can + exist while the mailbox "Customers" does not. As CHILDINFO extended + data item is not allowed if the RECURSIVEMATCH selection option is + not specified, such servers SHOULD use the "\NonExistent + \HasChildren" attribute pair to signal to the client that there is a + descendant mailbox that matches the selection criteria. See example + 11 in Section 5. + + The returned selection criteria allow the client to distinguish a + solicited response from an unsolicited one, as well as to distinguish + among solicited responses caused by multiple pipelined LIST commands + that specify different criteria. + + Servers SHOULD ONLY return a non-matching mailbox name along with + CHILDINFO if at least one matching child is not also being returned. + That is, servers SHOULD suppress redundant CHILDINFO responses. + + Examples 8 and 10 in Section 5 demonstrate the difference between + present CHILDINFO extended data item and the "\HasChildren" + attribute. + + + + +Leiba & Melnikov Standards Track [Page 10] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + The following table summarizes interaction between the "\NonExistent" + attribute and CHILDINFO (the first column indicates whether the + parent mailbox exists): + + +--------+--------------+--------------------+----------------------+ + | exists | meets the | has a child that | returned | + | | selection | meets the | LIST-EXTENDED | + | | criteria | selection criteria | attributes and | + | | | | CHILDINFO | + +--------+--------------+--------------------+----------------------+ + | no | no | no | no LIST response | + | | | | returned | + | yes | no | no | no LIST response | + | | | | returned | + | no | yes | no | (\NonExistent | + | | | | <attr>) | + | yes | yes | no | (<attr>) | + | no | no | yes | (\NonExistent) + | + | | | | CHILDINFO | + | yes | no | yes | () + CHILDINFO | + | no | yes | yes | (\NonExistent | + | | | | <attr>) + CHILDINFO | + | yes | yes | yes | (<attr>) + CHILDINFO | + +--------+--------------+--------------------+----------------------+ + + where <attr> is one or more attributes that correspond to the + selection criteria; for example, for the SUBSCRIBED option the <attr> + is \Subscribed. + +4. The CHILDREN Return Option + + The CHILDREN return option implements the Child Mailbox Extension, + originally proposed by Mike Gahrns and Raymond Cheng, of Microsoft + Corporation. Most of the information in this section is taken + directly from their original specification [CMbox]. The CHILDREN + return option is simply an indication that the client wants this + information; a server MAY provide it even if the option is not + specified. + + Many IMAP4 [IMAP4] clients present to the user a hierarchical view of + the mailboxes that a user has access to. Rather than initially + presenting to the user the entire mailbox hierarchy, it is often + preferable to show to the user a collapsed outline list of the + mailbox hierarchy (particularly if there is a large number of + mailboxes). The user can then expand the collapsed outline hierarchy + as needed. It is common to include within the collapsed hierarchy a + visual clue (such as a ''+'') to indicate that there are child + mailboxes under a particular mailbox. When the visual clue is + + + +Leiba & Melnikov Standards Track [Page 11] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + clicked, the hierarchy list is expanded to show the child mailboxes. + The CHILDREN return option provides a mechanism for a client to + efficiently determine whether a particular mailbox has children, + without issuing a LIST "" * or a LIST "" % for each mailbox name. + The CHILDREN return option defines two new attributes that MUST be + returned within a LIST response: \HasChildren and \HasNoChildren. + Although these attributes MAY be returned in response to any LIST + command, the CHILDREN return option is provided to indicate that the + client particularly wants this information. If the CHILDREN return + option is present, the server MUST return these attributes even if + their computation is expensive. + + \HasChildren + + The presence of this attribute indicates that the mailbox has child + mailboxes. A server SHOULD NOT set this attribute if there are + child mailboxes and the user does not have permission to access + any of them. In this case, \HasNoChildren SHOULD be used. In + many cases, however, a server may not be able to efficiently + compute whether a user has access to any child mailbox. Note + that even though the \HasChildren attribute for a mailbox must + be correct at the time of processing of the mailbox, a client + must be prepared to deal with a situation when a mailbox is + marked with the \HasChildren attribute, but no child mailbox + appears in the response to the LIST command. This might happen, + for example, due to children mailboxes being deleted or made + inaccessible to the user (using access control) by another + client before the server is able to list them. + + \HasNoChildren + + The presence of this attribute indicates that the mailbox has NO + child mailboxes that are accessible to the currently + authenticated user. + + It is an error for the server to return both a \HasChildren and a + \HasNoChildren attribute in the same LIST response. + + Note: the \HasNoChildren attribute should not be confused with the + IMAP4 [IMAP4] defined attribute \NoInferiors, which indicates that no + child mailboxes exist now and none can be created in the future. + + + + + + + + + + +Leiba & Melnikov Standards Track [Page 12] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + +5. Examples + + 1: The first example shows the complete local hierarchy that will + be used for the other examples. + + C: A01 LIST "" "*" + S: * LIST (\Marked \NoInferiors) "/" "inbox" + S: * LIST () "/" "Fruit" + S: * LIST () "/" "Fruit/Apple" + S: * LIST () "/" "Fruit/Banana" + S: * LIST () "/" "Tofu" + S: * LIST () "/" "Vegetable" + S: * LIST () "/" "Vegetable/Broccoli" + S: * LIST () "/" "Vegetable/Corn" + S: A01 OK done + + 2: In the next example, we will see the subscribed mailboxes. This + is similar to, but not equivalent with, <LSUB "" "*">. Note + that the mailbox called "Fruit/Peach" is subscribed to, but does + not actually exist (perhaps it was deleted while still + subscribed). The "Fruit" mailbox is not subscribed to, but it + has two subscribed children. The "Vegetable" mailbox is + subscribed and has two children; one of them is subscribed as + well. + + C: A02 LIST (SUBSCRIBED) "" "*" + S: * LIST (\Marked \NoInferiors \Subscribed) "/" "inbox" + S: * LIST (\Subscribed) "/" "Fruit/Banana" + S: * LIST (\Subscribed \NonExistent) "/" "Fruit/Peach" + S: * LIST (\Subscribed) "/" "Vegetable" + S: * LIST (\Subscribed) "/" "Vegetable/Broccoli" + S: A02 OK done + + 3: The next example shows the use of the CHILDREN option. The + client, without having to list the second level of hierarchy, + now knows which of the top-level mailboxes have submailboxes + (children) and which do not. Note that it's not necessary for + the server to return the \HasNoChildren attribute for the inbox, + because the \NoInferiors attribute already implies that, and has + a stronger meaning. + + C: A03 LIST () "" "%" RETURN (CHILDREN) + S: * LIST (\Marked \NoInferiors) "/" "inbox" + S: * LIST (\HasChildren) "/" "Fruit" + S: * LIST (\HasNoChildren) "/" "Tofu" + S: * LIST (\HasChildren) "/" "Vegetable" + S: A03 OK done + + + + +Leiba & Melnikov Standards Track [Page 13] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + 4: In this example, we see more mailboxes that reside on another + server. This is similar to the command <RLIST "" "%">. + + C: A04 LIST (REMOTE) "" "%" RETURN (CHILDREN) + S: * LIST (\Marked \NoInferiors) "/" "inbox" + S: * LIST (\HasChildren) "/" "Fruit" + S: * LIST (\HasNoChildren) "/" "Tofu" + S: * LIST (\HasChildren) "/" "Vegetable" + S: * LIST (\Remote) "/" "Bread" + S: * LIST (\HasChildren \Remote) "/" "Meat" + S: A04 OK done + + 5: The following example also requests the server to include + mailboxes that reside on another server. The server returns + information about all mailboxes that are subscribed. This is + similar to the command <RLSUB "" "*">. We also see the use of + two selection options. + + C: A05 LIST (REMOTE SUBSCRIBED) "" "*" + S: * LIST (\Marked \NoInferiors \Subscribed) "/" "inbox" + S: * LIST (\Subscribed) "/" "Fruit/Banana" + S: * LIST (\Subscribed \NonExistent) "/" "Fruit/Peach" + S: * LIST (\Subscribed) "/" "Vegetable" + S: * LIST (\Subscribed) "/" "Vegetable/Broccoli" + S: * LIST (\Remote \Subscribed) "/" "Bread" + S: A05 OK done + + 6: The following example requests the server to include mailboxes + that reside on another server. The server is asked to return + subscription information for all returned mailboxes. This is + different from the example above. + + Note that the output of this command is not a superset of the + output in the previous example, as it doesn't include LIST + response for the non-existent "Fruit/Peach". + + C: A06 LIST (REMOTE) "" "*" RETURN (SUBSCRIBED) + S: * LIST (\Marked \NoInferiors \Subscribed) "/" "inbox" + S: * LIST () "/" "Fruit" + S: * LIST () "/" "Fruit/Apple" + S: * LIST (\Subscribed) "/" "Fruit/Banana" + S: * LIST () "/" "Tofu" + S: * LIST (\Subscribed) "/" "Vegetable" + S: * LIST (\Subscribed) "/" "Vegetable/Broccoli" + S: * LIST () "/" "Vegetable/Corn" + S: * LIST (\Remote \Subscribed) "/" "Bread" + S: * LIST (\Remote) "/" "Meat" + S: A06 OK done + + + +Leiba & Melnikov Standards Track [Page 14] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + 7: In the following example, the client has specified multiple + mailbox patterns. Note that this example does not use the + mailbox hierarchy used in the previous examples. + + C: BBB LIST "" ("INBOX" "Drafts" "Sent/%") + S: * LIST () "/" "INBOX" + S: * LIST (\NoInferiors) "/" "Drafts" + S: * LIST () "/" "Sent/March2004" + S: * LIST (\Marked) "/" "Sent/December2003" + S: * LIST () "/" "Sent/August2004" + S: BBB OK done + + 8: The following example demonstrates the difference between the + \HasChildren attribute and the CHILDINFO extended data item. + + Let's assume there is the following hierarchy: + + C: C01 LIST "" "*" + S: * LIST (\Marked \NoInferiors) "/" "inbox" + S: * LIST () "/" "Foo" + S: * LIST () "/" "Foo/Bar" + S: * LIST () "/" "Foo/Baz" + S: * LIST () "/" "Moo" + S: C01 OK done + + If the client asks RETURN (CHILDREN), it will get this: + + C: CA3 LIST "" "%" RETURN (CHILDREN) + S: * LIST (\Marked \NoInferiors) "/" "inbox" + S: * LIST (\HasChildren) "/" "Foo" + S: * LIST (\HasNoChildren) "/" "Moo" + S: CA3 OK done + + A) Let's also assume that the mailbox "Foo/Baz" is the only + subscribed mailbox. Then we get this result: + + C: C02 LIST (SUBSCRIBED) "" "*" + S: * LIST (\Subscribed) "/" "Foo/Baz" + S: C02 OK done + + Now, if the client issues <LIST (SUBSCRIBED) "" "%">, the server will + return no mailboxes (as the mailboxes "Moo", "Foo", and "Inbox" are + NOT subscribed). However, if the client issues this: + + C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%" + S: * LIST () "/" "Foo" ("CHILDINFO" ("SUBSCRIBED")) + S: C04 OK done + + + + +Leiba & Melnikov Standards Track [Page 15] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + (i.e., the mailbox "Foo" is not subscribed, but it has a child that + is.) + + A1) If the mailbox "Foo" had also been subscribed, the last command + would return this: + + C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%" + S: * LIST (\Subscribed) "/" "Foo" ("CHILDINFO" ("SUBSCRIBED")) + S: C04 OK done + + or even this: + + C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%" + S: * LIST (\Subscribed \HasChildren) "/" "Foo" ("CHILDINFO" + ("SUBSCRIBED")) + S: C04 OK done + + A2) If we assume instead that the mailbox "Foo" is not part of the + original hierarchy and is not subscribed, the last command will give + this result: + + C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%" + S: * LIST (\NonExistent) "/" "Foo" ("CHILDINFO" ("SUBSCRIBED")) + S: C04 OK done + + B) Now, let's assume that no mailbox is subscribed. In this case, + the command <LIST (SUBSCRIBED RECURSIVEMATCH) "" "%"> will return no + responses, as there are no subscribed children (even though "Foo" has + children). + + C) And finally, suppose that only the mailboxes "Foo" and "Moo" are + subscribed. In that case, we see this result: + + C: C04 LIST (SUBSCRIBED RECURSIVEMATCH) "" "%" RETURN (CHILDREN) + S: * LIST (\HasChildren \Subscribed) "/" "Foo" + S: * LIST (\HasNoChildren \Subscribed) "/" "Moo" + S: C04 OK done + + (which means that the mailbox "Foo" has children, but none of them is + subscribed). + + 9: The following example demonstrates that the CHILDINFO extended + data item is returned whether or not children mailboxes match + the canonical LIST pattern. + + + + + + + +Leiba & Melnikov Standards Track [Page 16] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + Let's assume there is the following hierarchy: + + C: D01 LIST "" "*" + S: * LIST (\Marked \NoInferiors) "/" "inbox" + S: * LIST () "/" "foo2" + S: * LIST () "/" "foo2/bar1" + S: * LIST () "/" "foo2/bar2" + S: * LIST () "/" "baz2" + S: * LIST () "/" "baz2/bar2" + S: * LIST () "/" "baz2/bar22" + S: * LIST () "/" "baz2/bar222" + S: * LIST () "/" "eps2" + S: * LIST () "/" "eps2/mamba" + S: * LIST () "/" "qux2/bar2" + S: D01 OK done + + And that the following mailboxes are subscribed: + + C: D02 LIST (SUBSCRIBED) "" "*" + S: * LIST (\Subscribed) "/" "foo2/bar1" + S: * LIST (\Subscribed) "/" "foo2/bar2" + S: * LIST (\Subscribed) "/" "baz2/bar2" + S: * LIST (\Subscribed) "/" "baz2/bar22" + S: * LIST (\Subscribed) "/" "baz2/bar222" + S: * LIST (\Subscribed) "/" "eps2" + S: * LIST (\Subscribed) "/" "eps2/mamba" + S: * LIST (\Subscribed) "/" "qux2/bar2" + S: D02 OK done + + The client issues the following command first: + + C: D03 LIST (RECURSIVEMATCH SUBSCRIBED) "" "*2" + S: * LIST () "/" "foo2" ("CHILDINFO" ("SUBSCRIBED")) + S: * LIST (\Subscribed) "/" "foo2/bar2" + S: * LIST (\Subscribed) "/" "baz2/bar2" + S: * LIST (\Subscribed) "/" "baz2/bar22" + S: * LIST (\Subscribed) "/" "baz2/bar222" + S: * LIST (\Subscribed) "/" "eps2" ("CHILDINFO" ("SUBSCRIBED")) + S: * LIST (\Subscribed) "/" "qux2/bar2" + S: D03 OK done + + and the server may also include (but this would violate a SHOULD NOT + in Section 3.5, because CHILDINFO is redundant) + + S: * LIST () "/" "baz2" ("CHILDINFO" ("SUBSCRIBED")) + S: * LIST (\NonExistent) "/" "qux2" ("CHILDINFO" ("SUBSCRIBED")) + + + + + +Leiba & Melnikov Standards Track [Page 17] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + The CHILDINFO extended data item is returned for mailboxes "foo2", + "baz2", and "eps2", because all of them have subscribed children, + even though for the mailbox "foo2" only one of the two subscribed + children matches the pattern, for the mailbox "baz2" all the + subscribed children match the pattern, and for the mailbox "eps2" + none of the subscribed children matches the pattern. + + Note that if the client issues + + C: D03 LIST (RECURSIVEMATCH SUBSCRIBED) "" "*" + S: * LIST () "/" "foo2" ("CHILDINFO" ("SUBSCRIBED")) + S: * LIST (\Subscribed) "/" "foo2/bar1" + S: * LIST (\Subscribed) "/" "foo2/bar2" + S: * LIST () "/" "baz2" ("CHILDINFO" ("SUBSCRIBED")) + S: * LIST (\Subscribed) "/" "baz2/bar2" + S: * LIST (\Subscribed) "/" "baz2/bar22" + S: * LIST (\Subscribed) "/" "baz2/bar222" + S: * LIST (\Subscribed) "/" "eps2" ("CHILDINFO" ("SUBSCRIBED")) + S: * LIST (\Subscribed) "/" "eps2/mamba" + S: * LIST (\Subscribed) "/" "qux2/bar2" + S: D03 OK done + + The LIST responses for mailboxes "foo2", "baz2", and "eps2" still + have the CHILDINFO extended data item, even though this information + is redundant and the client can determine it by itself. + + 10: The following example shows usage of multiple mailbox patterns. + It also demonstrates that the presence of the CHILDINFO extended + data item doesn't necessarily imply \HasChildren. + + C: a1 LIST "" ("foo" "foo/*") + S: * LIST () "/" foo + S: a1 OK done + + C: a2 LIST (SUBSCRIBED) "" "foo/*" + S: * LIST (\Subscribed \NonExistent) "/" foo/bar + S: a2 OK done + + C: a3 LIST (SUBSCRIBED RECURSIVEMATCH) "" foo RETURN (CHILDREN) + S: * LIST (\HasNoChildren) "/" foo ("CHILDINFO" ("SUBSCRIBED")) + S: a3 OK done + + 11: The following example shows how a server that supports missing + mailbox hierarchy elements can signal to a client that didn't + specify the RECURSIVEMATCH selection option that there is a + child mailbox that matches the selection criteria. + + + + + +Leiba & Melnikov Standards Track [Page 18] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + C: a1 LIST (REMOTE) "" * + S: * LIST () "/" music/rock + S: * LIST (\Remote) "/" also/jazz + S: a1 OK done + + C: a2 LIST () "" % + S: * LIST (\NonExistent \HasChildren) "/" music + S: a2 OK done + + C: a3 LIST (REMOTE) "" % + S: * LIST (\NonExistent \HasChildren) "/" music + S: * LIST (\NonExistent \HasChildren) "/" also + S: a3 OK done + + C: a3.1 LIST "" (% music/rock) + S: * LIST () "/" music/rock + S: a3.1 OK done + + Because "music/rock" is the only mailbox under "music", there's no + need for the server to also return "music". However clients must + handle both cases. + +6. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) as described in [ABNF]. Terms not defined here are taken + from [IMAP4]. In particular, note that the version of "mailbox-list" + below, which defines the payload of the LIST response, updates the + version defined in the IMAP specification. It is pointed to by + "mailbox-data", which is defined in [IMAP4]. + + "vendor-token" is defined in [ACAP]. Note that this normative + reference to ACAP will be an issue in moving this spec forward, since + it introduces a dependency on ACAP. The definitions of + "vendor-token" and of the IANA registry must eventually go somewhere + else, in a document that can be moved forward on the standards track + independently of ACAP. + + + + + + + + + + + + + + +Leiba & Melnikov Standards Track [Page 19] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + childinfo-extended-item = "CHILDINFO" SP "(" + list-select-base-opt-quoted + *(SP list-select-base-opt-quoted) ")" + ; Extended data item (mbox-list-extended-item) + ; returned when the RECURSIVEMATCH + ; selection option is specified. + ; Note 1: the CHILDINFO tag can be returned + ; with and without surrounding quotes, as per + ; mbox-list-extended-item-tag production. + ; Note 2: The selection options are always returned + ; quoted, unlike their specification in + ; the extended LIST command. + + child-mbox-flag = "\HasChildren" / "\HasNoChildren" + ; attributes for CHILDREN return option, at most one + ; possible per LIST response + + eitem-standard-tag = atom + ; a tag for extended list data defined in a Standard + ; Track or Experimental RFC. + + eitem-vendor-tag = vendor-token "-" atom + ; a vendor-specific tag for extended list data + + list = "LIST" [SP list-select-opts] SP mailbox SP mbox-or-pat + [SP list-return-opts] + + list-return-opts = "RETURN" SP + "(" [return-option *(SP return-option)] ")" + ; list return options, e.g., CHILDREN + + list-select-base-opt = "SUBSCRIBED" / option-extension + ; options that can be used by themselves + + list-select-base-opt-quoted = DQUOTE list-select-base-opt DQUOTE + + list-select-independent-opt = "REMOTE" / option-extension + ; options that do not syntactically interact with + ; other options + + list-select-mod-opt = "RECURSIVEMATCH" / option-extension + ; options that require a list-select-base-opt + ; to also be present + + list-select-opt = list-select-base-opt / list-select-independent-opt + / list-select-mod-opt + ; An option registration template is described in + ; Section 9.3 of this document. + + + +Leiba & Melnikov Standards Track [Page 20] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + list-select-opts = "(" [ + (*(list-select-opt SP) list-select-base-opt + *(SP list-select-opt)) + / (list-select-independent-opt + *(SP list-select-independent-opt)) + ] ")" + ; Any number of options may be in any order. + ; If a list-select-mod-opt appears, then a + ; list-select-base-opt must also appear. + ; This allows these: + ; () + ; (REMOTE) + ; (SUBSCRIBED) + ; (SUBSCRIBED REMOTE) + ; (SUBSCRIBED RECURSIVEMATCH) + ; (SUBSCRIBED REMOTE RECURSIVEMATCH) + ; But does NOT allow these: + ; (RECURSIVEMATCH) + ; (REMOTE RECURSIVEMATCH) + + mailbox-list = "(" [mbx-list-flags] ")" SP + (DQUOTE QUOTED-CHAR DQUOTE / nil) SP mailbox + [SP mbox-list-extended] + ; This is the list information pointed to by the ABNF + ; item "mailbox-data", which is defined in [IMAP4] + + mbox-list-extended = "(" [mbox-list-extended-item + *(SP mbox-list-extended-item)] ")" + + mbox-list-extended-item = mbox-list-extended-item-tag SP + tagged-ext-val + + mbox-list-extended-item-tag = astring + ; The content MUST conform to either "eitem-vendor-tag" + ; or "eitem-standard-tag" ABNF productions. + ; A tag registration template is described in this + ; document in Section 9.5. + + mbx-list-oflag =/ child-mbox-flag / "\Subscribed" / "\Remote" + + mbx-list-sflag =/ "\NonExistent" + + mbox-or-pat = list-mailbox / patterns + + option-extension = (option-standard-tag / option-vendor-tag) + [SP option-value] + + + + + +Leiba & Melnikov Standards Track [Page 21] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + option-standard-tag = atom + ; an option defined in a Standards Track or + ; Experimental RFC + + option-val-comp = astring / + option-val-comp *(SP option-val-comp) / + "(" option-val-comp ")" + + option-value = "(" option-val-comp ")" + + option-vendor-tag = vendor-token "-" atom + ; a vendor-specific option, non-standard + + patterns = "(" list-mailbox *(SP list-mailbox) ")" + + return-option = "SUBSCRIBED" / "CHILDREN" / option-extension + + tagged-ext-comp = astring / + tagged-ext-comp *(SP tagged-ext-comp) / + "(" tagged-ext-comp ")" + ; Extensions that follow this general + ; syntax should use nstring instead of + ; astring when appropriate in the context + ; of the extension. + ; Note that a message set or a "number" + ; can always be represented as an "atom". + ; A URL should be represented as + ; a "quoted" string. + + tagged-ext-simple = sequence-set / number + + tagged-ext-val = tagged-ext-simple / + "(" [tagged-ext-comp] ")" + +7. Internationalization Considerations + + The LIST command selection option types defined in this specification + involve simple tests of mailbox properties. However, future + extensions to LIST-EXTENDED may define selection options that do more + sophisticated tests. In the case of a test that requires matching + text, in the presence of the COMPARATOR [I18N] extension, the active + comparator must be used to do comparisons. Such LIST-EXTENDED + extensions MUST indicate in their specification the interaction with + the COMPARATOR [I18N] extension. + + + + + + + +Leiba & Melnikov Standards Track [Page 22] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + +8. Security Considerations + + This document describes syntactic changes to the specification of the + IMAP4 commands LIST, LSUB, RLIST, and RLSUB, and the modified LIST + command has the same security considerations as those commands. They + are described in [IMAP4] and [MBRef]. + + The Child Mailbox Extension provides a client a more efficient means + of determining whether a particular mailbox has children. If a + mailbox has children, but the currently authenticated user does not + have access to any of them, the server SHOULD respond with a + \HasNoChildren attribute. In many cases, however, a server may not + be able to efficiently compute whether a user has access to any child + mailbox. If such a server responds with a \HasChildren attribute, + when in fact the currently authenticated user does not have access to + any child mailboxes, potentially more information is conveyed about + the mailbox than intended. In most situations, this will not be a + security concern, because if information regarding whether a mailbox + has children is considered sensitive, a user would not be granted + access to that mailbox in the first place. + + The CHILDINFO extended data item has the same security considerations + as the \HasChildren attribute described above. + +9. IANA Considerations + +9.1. Guidelines for IANA + + IANA has created two new registries for LIST-EXTENDED options and + LIST-EXTENDED response data. The templates and the initial + registrations are detailed below. + +9.2. Registration Procedure and Change Control + + Registration of a LIST-EXTENDED option is done by filling in the + template in Section 9.3 and sending it via electronic mail to + iana@iana.org. Registration of a LIST-EXTENDED extended data item is + done by filling in the template in Section 9.5 and sending it via + electronic mail to iana@iana.org. IANA has the right to reject + obviously bogus registrations, but will perform no review of claims + made in the registration form. + + A LIST-EXTENDED option/extended data item name that starts with "V-" + is reserved for vendor-specific options/extended data items. All + options, whether they are vendor specific or global, should be + registered with IANA. If a LIST-EXTENDED extended data item is + returned as a result of requesting a particular LIST-EXTENDED option, + + + + +Leiba & Melnikov Standards Track [Page 23] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + the name of the option SHOULD be used as the name of the + LIST-EXTENDED extended data item. + + Each vendor-specific option/extended data item MUST start with its + vendor-token ("vendor prefix"). The vendor-token MUST be registered + with IANA, using the [ACAP] vendor subtree registry. + + Standard LIST-EXTENDED option/extended data item names are case + insensitive. If the vendor prefix is omitted from a vendor-specific + LIST-EXTENDED option/extended data item name, the rest is case + insensitive. The vendor prefix itself is not case sensitive, as it + might contain non-ASCII characters. While the registration + procedures do not require it, authors of + LIST-EXTENDED options/extended data items are encouraged to seek + community review and comment whenever that is feasible. Authors may + seek community review by posting a specification of their proposed + mechanism as an + Internet-Draft. LIST-EXTENDED option/extended data items intended + for widespread use should be standardized through the normal IETF + process, when appropriate. + + Comments on registered LIST-EXTENDED options/extended response data + should first be sent to the "owner" of the mechanism and/or to the + IMAPEXT WG mailing list. Submitters of comments may, after a + reasonable attempt to contact the owner, request IANA to attach their + comment to the registration itself. If IANA approves of this, the + comment will be made accessible in conjunction with the registration + LIST-EXTENDED options/extended response data itself. + + Once a LIST-EXTENDED registration has been published by IANA, the + author may request a change to its definition. The change request + follows the same procedure as the registration request. + + The owner of a LIST-EXTENDED registration may pass responsibility for + the registered option/extended data item to another person or agency + by informing IANA; this can be done without discussion or review. + + The IESG may reassign responsibility for a LIST-EXTENDED + option/extended data item. The most common case of this will be to + enable changes to be made to mechanisms where the author of the + registration has died, has moved out of contact, or is otherwise + unable to make changes that are important to the community. + + LIST-EXTENDED registrations may not be deleted; mechanisms that are + no longer believed appropriate for use can be declared OBSOLETE by a + change to their "intended use" field. Such LIST-EXTENDED + options/extended data items will be clearly marked in the lists + published by IANA. + + + +Leiba & Melnikov Standards Track [Page 24] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + The IESG is considered to be the owner of all LIST-EXTENDED + options/extended data items that are on the IETF standards track. + +9.3. Registration Template for LIST-EXTENDED Options + + To: iana@iana.org + Subject: Registration of LIST-EXTENDED option X + + LIST-EXTENDED option name: + + LIST-EXTENDED option type: (One of SELECTION or RETURN) + + Implied return options(s), if the option type is SELECTION: (zero or + more) + + LIST-EXTENDED option description: + + Published specification (optional, recommended): + + Security considerations: + + Intended usage: + (One of COMMON, LIMITED USE, or OBSOLETE) + + Person and email address to contact for further information: + + Owner/Change controller: + + (Any other information that the author deems interesting may be added + below this line.) + +9.4. Initial LIST-EXTENDED Option Registrations + + The LIST-EXTENDED option registry has been populated with the + following entries: + + 1. To: iana@iana.org + Subject: Registration of LIST-EXTENDED option SUBSCRIBED + + LIST-EXTENDED option name: SUBSCRIBED + + LIST-EXTENDED option type: SELECTION + + Implied return options(s): SUBSCRIBED + + LIST-EXTENDED option description: Causes the LIST command to list + subscribed mailboxes, rather than the actual mailboxes. + + + + +Leiba & Melnikov Standards Track [Page 25] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + Published specification: RFC 5258, Section 3. + + Security considerations: RFC 5258, Section 8. + + Intended usage: COMMON + + Person and email address to contact for further information: + Alexey Melnikov <Alexey.Melnikov@isode.com> + + Owner/Change controller: iesg@ietf.org + + 2. To: iana@iana.org + Subject: Registration of LIST-EXTENDED option REMOTE + + LIST-EXTENDED option name: REMOTE + + LIST-EXTENDED option type: SELECTION + + Implied return options(s): (none) + + LIST-EXTENDED option description: Causes the LIST command to + return remote mailboxes as well as local ones, as described in + RFC 2193. + + Published specification: RFC 5258, Section 3. + + Security considerations: RFC 5258, Section 8. + + Intended usage: COMMON + + Person and email address to contact for further information: + Alexey Melnikov <Alexey.Melnikov@isode.com> + + Owner/Change controller: iesg@ietf.org + + 3. To: iana@iana.org + Subject: Registration of LIST-EXTENDED option SUBSCRIBED + + LIST-EXTENDED option name: SUBSCRIBED + + LIST-EXTENDED option type: RETURN + + LIST-EXTENDED option description: Causes the LIST command to + return subscription state. + + Published specification: RFC 5258, Section 3. + + Security considerations: RFC 5258, Section 8. + + + +Leiba & Melnikov Standards Track [Page 26] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + Intended usage: COMMON + + Person and email address to contact for further information: + Alexey Melnikov <Alexey.Melnikov@isode.com> + + Owner/Change controller: iesg@ietf.org + + 4. To: iana@iana.org + Subject: Registration of LIST-EXTENDED option RECURSIVEMATCH + + LIST-EXTENDED option name: RECURSIVEMATCH + + LIST-EXTENDED option type: SELECTION + + Implied return options(s): (none) + + LIST-EXTENDED option description: Requests that CHILDINFO + extended data item (childinfo-extended-item) is to be returned. + + Published specification: RFC 5258, Section 3. + + Security considerations: RFC 5258, Section 8. + + Intended usage: COMMON + + Person and email address to contact for further information: + Alexey Melnikov <Alexey.Melnikov@isode.com> + + Owner/Change controller: iesg@ietf.org + + 5. To: iana@iana.org + Subject: Registration of LIST-EXTENDED option CHILDREN + + LIST-EXTENDED option name: CHILDREN + + LIST-EXTENDED option type: RETURN + + LIST-EXTENDED option description: Requests mailbox child + information. + + Published specification: RFC 5258, Section 3 and Section 4. + + Security considerations: RFC 5258, Section 8. + + Intended usage: COMMON + + Person and email address to contact for further information: + Alexey Melnikov <Alexey.Melnikov@isode.com> + + + +Leiba & Melnikov Standards Track [Page 27] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + Owner/Change controller: iesg@ietf.org + +9.5. Registration Template for LIST-EXTENDED Extended Data Item + + To: iana@iana.org + Subject: Registration of X LIST-EXTENDED extended data item + + LIST-EXTENDED extended data item tag: + + LIST-EXTENDED extended data item description: + + Which LIST-EXTENDED option(s) (and their types) causes this extended + data item to be returned (if any): + + Published specification (optional, recommended): + + Security considerations: + + Intended usage: + (One of COMMON, LIMITED USE, or OBSOLETE) + + Person and email address to contact for further information: + + Owner/Change controller: + + (Any other information that the author deems interesting may be added + below this line.) + +9.6. Initial LIST-EXTENDED Extended Data Item Registrations + + The LIST-EXTENDED extended data item registry has been populated with + the following entries: + + 1. To: iana@iana.org + Subject: Registration of CHILDINFO LIST-EXTENDED extended data + item + + LIST-EXTENDED extended data item tag: CHILDINFO + + LIST-EXTENDED extended data item description: The CHILDINFO + extended data item describes the selection criteria that has + caused it to be returned and indicates that the mailbox has one + or more child mailboxes that match the selection criteria. + + Which LIST-EXTENDED option(s) (and their types) causes this + extended data item to be returned (if any): RECURSIVEMATCH + selection option + + + + +Leiba & Melnikov Standards Track [Page 28] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + + Published specification: RFC 5258, Section 3.5. + + Security considerations: RFC 5258, Section 8. + + Intended usage: COMMON + + Person and email address to contact for further information: + Alexey Melnikov <Alexey.Melnikov@isode.com> + + Owner/Change controller: iesg@ietf.org + +10. Acknowledgements + + Mike Gahrns and Raymond Cheng of Microsoft Corporation originally + devised the Child Mailbox Extension and proposed it in 1997; the + idea, as well as most of the text in Section 4, is theirs. + + This document is the result of discussions on the IMAP4 and IMAPEXT + mailing lists and is meant to reflect consensus of those groups. In + particular, Mark Crispin, Philip Guenther, Cyrus Daboo, Timo + Sirainen, Ken Murchison, Rob Siemborski, Steve Hole, Arnt + Gulbrandsen, Larry Greenfield, Dave Cridland, and Pete Maclean were + active participants in those discussions or made suggestions to this + document. + +11. References + +11.1. Normative References + + [ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", STD 68, RFC 5234, January 2008. + + [ACAP] Newman, C. and J. Myers, "ACAP -- Application Configuration + Access Protocol", RFC 2244, November 1997. + + [I18N] Newman, C., Gulbrandsen, A., and A. Melnikov, "Internet + Message Access Protocol Internationalization", RFC 5255, + June 2008. + + [IMAP4] Crispin, M., "Internet Message Access Protocol - Version + 4rev1", RFC 3501, March 2003. + + [Kwds] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", RFC 2119, March 1997. + + [MBRef] Gahrns, M., "IMAP4 Mailbox Referrals", RFC 2193, + September 1997. + + + + +Leiba & Melnikov Standards Track [Page 29] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + +11.2. Informative References + + [CMbox] Gahrns, M. and R. Cheng, "The Internet Message Action + Protocol (IMAP4) Child Mailbox Extension", RFC 3348, + July 2002. + +Authors' Addresses + + Barry Leiba + IBM T.J. Watson Research Center + 19 Skyline Drive + Hawthorne, NY 10532 + US + + Phone: +1 914 784 7941 + EMail: leiba@watson.ibm.com + + + Alexey Melnikov + Isode Limited + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: Alexey.Melnikov@isode.com + URI: http://www.melnikov.ca/ + + + + + + + + + + + + + + + + + + + + + + + + +Leiba & Melnikov Standards Track [Page 30] + +RFC 5258 IMAP4 LIST Command Extensions June 2008 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2008). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Leiba & Melnikov Standards Track [Page 31] + diff --git a/imap/docs/rfc/rfc5259.txt b/imap/docs/rfc/rfc5259.txt new file mode 100644 index 00000000..9d6ab8ad --- /dev/null +++ b/imap/docs/rfc/rfc5259.txt @@ -0,0 +1,1683 @@ + + + + + + +Network Working Group A. Melnikov, Ed. +Request for Comments: 5259 Isode Ltd +Category: Standards Track P. Coates, Ed. + Sun Microsystems + July 2008 + + + Internet Message Access Protocol - CONVERT Extension + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + CONVERT defines extensions to IMAP allowing clients to request + adaptation and/or transcoding of attachments. Clients can specify + the conversion details or allow servers to decide based on knowledge + of client capabilities, on user or administrator preferences, or on + server settings. + + + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov & Coates Standards Track [Page 1] + +RFC 5259 IMAP CONVERT extension July 2008 + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 + 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 + 3. Relation with Other IMAP Specifications . . . . . . . . . . . 4 + 3.1. CAPABILITY Response . . . . . . . . . . . . . . . . . . . 4 + 4. Scope of Conversions . . . . . . . . . . . . . . . . . . . . . 4 + 5. Discovery of Available Conversions . . . . . . . . . . . . . . 4 + 5.1. CONVERSIONS Command . . . . . . . . . . . . . . . . . . . 4 + 5.2. CONVERSION Response . . . . . . . . . . . . . . . . . . . 6 + 6. CONVERT and UID CONVERT Commands . . . . . . . . . . . . . . . 6 + 7. CONVERT Conversion Parameters . . . . . . . . . . . . . . . . 12 + 7.1. Mandatory-to-Implement Conversions and Conversion + Parameters . . . . . . . . . . . . . . . . . . . . . . . . 12 + 7.2. Additional Features for Mobile Usage . . . . . . . . . . . 13 + 8. Request/Response Data Items to CONVERT/UID CONVERT Commands . 14 + 8.1. CONVERTED Untagged Response . . . . . . . . . . . . . . . 14 + 8.2. BODYPARTSTRUCTURE CONVERT Request and Response Item . . . 14 + 8.3. BINARY.SIZE CONVERT Request and Response Item . . . . . . 15 + 8.4. AVAILABLECONVERSIONS CONVERT Request and Response Item . . 16 + 8.5. Implementation Considerations . . . . . . . . . . . . . . 17 + 9. Status Responses and Response Code Extensions . . . . . . . . 17 + 10. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 20 + 11. Manageability Considerations . . . . . . . . . . . . . . . . . 24 + 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 + 12.1. Registration of unknown-character-replacement Media + Type Parameter . . . . . . . . . . . . . . . . . . . . . . 25 + 13. Security Considerations . . . . . . . . . . . . . . . . . . . 26 + 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27 + 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 + 15.1. Normative References . . . . . . . . . . . . . . . . . . . 28 + 15.2. Informative References . . . . . . . . . . . . . . . . . . 29 + + + + + + + + + + + + + + + + + + + +Melnikov & Coates Standards Track [Page 2] + +RFC 5259 IMAP CONVERT extension July 2008 + + +1. Introduction + + This document defines the CONVERT extension to IMAP4 [RFC3501]. + CONVERT provides adaptation and transcoding of body parts as needed + by the client. Conversion (adaptation, transcoding) may be requested + by the client and performed by the server on a best effort basis or, + when requested by the client, decided by the server based on the + server's knowledge of the client capabilities, user or administrator + preferences, or server settings. + + This extension is primarily intended to be useful to mobile clients. + It satisfies requirements specified in [OMA-ME-RD]. + + A server that supports CONVERT can convert body parts to other + formats to be viewed (for example) on a mobile device. The client + can explicitly request a particular conversion or ask the server to + select the best available conversion. When allowed by the client, + the server determines how to convert based on its own strategy (e.g., + based on knowledge of the client as discussed hereafter). If the + server knows the characteristics of the device (out of scope for + CONVERT) or can determine them (for example, using a conversion + parameter containing device type), converted body parts can also be + optimized for capabilities of the device (e.g., form factor of + pictures). The client is able to control conversions using optional + conversion (also referred to as "transcoding" in this document) + parameters. + + This document relies on the registry of conversion parameters + established by [MEDIAFEAT-REG]. The registry can be used to discover + the underlying legal values that these parameters can take. + Additional conversion parameters, such as those defined by [OMA-STI], + are expected to be registered in the future. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. If a single "C:" or "S:" label applies to + multiple lines, then the line breaks between those lines are for + editorial clarity only and are not part of the actual protocol + exchange. The five characters [...] mean that something has been + elided. + + + + + + +Melnikov & Coates Standards Track [Page 3] + +RFC 5259 IMAP CONVERT extension July 2008 + + + When describing the general syntax, some definitions are omitted as + they are defined in [RFC3501]. In particular, the term "session" is + used in this document as defined in Section 1.2 of [RFC3501]. + +3. Relation with Other IMAP Specifications + + Conversion of attachments during streaming is out of scope for the + CONVERT extension and is described in a separate Lemonade WG document + [LEM-STREAMING]. + + A server claiming compliance with this specification MUST support the + IMAP Binary specification [RFC3516]. + +3.1. CAPABILITY Response + + A server that supports the CONVERT extension MUST return "CONVERT" + and "BINARY" in the CAPABILITY response or response code. (Client + and server authors are reminded that the order of tokens returned in + the CAPABILITY response or response code is arbitrary.) + + Example: A server that implements CONVERT. + + C: a000 CAPABILITY + S: * CAPABILITY IMAP4rev1 CONVERT BINARY [...] + S: a000 OK CAPABILITY completed + +4. Scope of Conversions + + Conversions only affect what is sent to the client; the original data + in the message store MUST NOT be altered. This document does not + specify how the server performs conversions. + + Note: The requirement that original data be unaltered allows such + data to remain accessible by other clients, permits replies or + forwards of the original documents, permits signature verification + (the converted body parts are not likely to contain any signatures), + and preserves BODYSTRUCTURE and related information. + +5. Discovery of Available Conversions + +5.1. CONVERSIONS Command + + Arguments: source MIME type + target MIME type + + Responses: untagged responses: CONVERSION + + + + + +Melnikov & Coates Standards Track [Page 4] + +RFC 5259 IMAP CONVERT extension July 2008 + + + Result: OK - CONVERSIONS command completed + BAD - unrecognized syntax of an argument, unexpected extra + argument, missing argument, etc. + + The CONVERSIONS command is allowed in Authenticated and Selected IMAP + states. + + The first parameter to the CONVERSIONS command is a source MIME type, + the second parameter is the target MIME type. Both parameters are + partially (e.g., "text/*") or completely ("*") wildcardable. + + Conversions matching the source/target pair and their associated + conversion parameters are returned in untagged CONVERSION responses. + If source/target doesn't match any conversion supported by the + server, no CONVERSION response is returned. + + Examples: + + For conversion information from GIF to JPEG image format (no untagged + CONVERSION response would be returned if no conversion is possible): + + C: a CONVERSIONS "image/gif" "image/jpeg" + S: * CONVERSION "image/gif" "image/jpeg" ("pix-y" "pix-x" + "image-interleave") + S: a OK CONVERSIONS completed + + For conversion information from GIF image format to anything: + + C: b CONVERSIONS "image/gif" "*" + S: * CONVERSION "image/gif" "image/jpeg" ("pix-y" "pix-x" + "image-interleave") + S: * CONVERSION "image/gif" "image/png" ([...]) + [...] + S: b OK CONVERSIONS completed + + For conversion of anything to JPEG: + + C: c CONVERSIONS "*" "image/jpeg" + S: * CONVERSION "image/gif" "image/jpeg" ("pix-y" "pix-x" + "image-interleave") + S: * CONVERSION "image/png" "image/jpeg" (...) + [...] + S: c OK CONVERSIONS completed + + For conversions from all image formats to all text formats, the + client can issue the following command: + + C: d CONVERSIONS "image/*" "text/*" + + + +Melnikov & Coates Standards Track [Page 5] + +RFC 5259 IMAP CONVERT extension July 2008 + + +5.2. CONVERSION Response + + Contents: source MIME type + target MIME type + optional list of supported conversion parameters + + As a result of executing a CONVERSIONS command, the server can return + one or more CONVERSION responses. Each CONVERSION response specifies + which source MIME type can be converted to the target MIME type, and + also lists supported conversion parameters. + +6. CONVERT and UID CONVERT Commands + + Arguments: sequence set + conversion parameters + CONVERT data item names + + Responses: untagged responses: CONVERTED + + Result: OK - convert completed + NO - convert error: can't fetch and/or convert that data + BAD - unrecognized syntax of an argument, unexpected extra + argument, missing argument, etc. + + The CONVERT extension defines CONVERT and UID CONVERT commands that + are used to transcode the media type of a MIME part into another + media type, and/or the same media type with different encoding + parameters. These commands are structured and behave similarly to + FETCH/UID FETCH commands as extended by [RFC3516]: + + o A successful CONVERT/UID CONVERT command results in one or more + untagged CONVERTED responses (one per message). They are similar + to the untagged FETCH responses. Note that a single CONVERT/ UID + CONVERT command can only perform a single type of conversion as + defined by the conversion parameters. A client that needs to + perform multiple different conversions needs to issue multiple + CONVERT/UID CONVERT commands. Such a client MAY pipeline them. + + o BINARY[...] data item requests conversion of a body part or of the + whole message according to conversion parameters and requests that + the converted message/body part be returned as binary. + + o BINARY.SIZE data item is similar to RFC822.SIZE, but it requests + size of a converted body part/message. + + o BODYPARTSTRUCTURE data item is similar to BODYSTRUCTURE FETCH data + item, but it returns the MIME structure of the converted body + part. + + + +Melnikov & Coates Standards Track [Page 6] + +RFC 5259 IMAP CONVERT extension July 2008 + + + o BODY[...HEADER] encoded words in the requested headers are + converted to the specified charset. The CHARSET parameter is + REQUIRED for this conversion. + + o BODY[...MIME] encoded words in the requested headers are converted + to the specified charset. The CHARSET parameter is REQUIRED for + this conversion. + + o AVAILABLECONVERSIONS data item requests the list of target MIME + types the specified body part (or the whole message) can be + converted to. + + The CONVERT extension also adds one new response code. See Section 9 + for more details. + + Typically clients will request conversion of leaf body parts. In + addition to support of leaf body part conversion, servers MAY offer + conversion of non-leaf body parts (e.g., conversion from multipart/ + related). + + Instead of specifying the exact target MIME media type the client + wants to convert to, the client MAY use a special marker NIL (also + known as "default conversion") to request the server to pick a + suitable target media type. This document doesn't describe how + exactly the server makes such a choice; however, some basic + guidelines are described in this paragraph. If the server knows + characteristics of the device using an in-band (such as device type + specified in a conversion parameter) or an out-of-band mechanism, + then it should convert the request body part to a media type the + device is likely to support and display/play successfully. Unless + specifically overridden by a conversion parameter, the server MAY + also remove any unnecessary detail that exceeds the capabilities of + the device (e.g., scaling images to just fit on the device's screen). + In the absence of any in-band or out-of-band mechanism for + determining device characteristics, the server should convert the + request body part to the most standard or widely deployed media type + available in that media category, for example, to convert to text/ + plain, image/jpeg. In such case, the server should minimize quality + loss. Servers are REQUIRED to support "default conversion" requests. + Server implementations that support conversions to multiple target + MIME types SHOULD make the default conversion configurable. Clients + SHOULD avoid using the default conversion unless they provided a way + (in-band or out-band) to signal their capabilities to the server, as + there is no guaranty that the server would guess their capability + correctly. Client implementors should consider using + AVAILABLECONVERSIONS CONVERT data item or CONVERSIONS command instead + of the default conversion. + + + + +Melnikov & Coates Standards Track [Page 7] + +RFC 5259 IMAP CONVERT extension July 2008 + + + CONVERT's command syntax is modeled after the FETCH command syntax in + [RFC3501], as extended by [RFC3516]. CONVERT data items are + generally structured as: + + BINARY[section-part]<partial> + + BINARY.SIZE[section-part] + + BODYPARTSTRUCTURE[section-part] + + BODY[HEADER] + + BODY[section-part.HEADER] + + BODY[section-part.MIME] + + AVAILABLECONVERSIONS[section-part] + + The semantics of a partial CONVERT BINARY[...] command is the same as + for a partial FETCH BODY[...] command, with the exception that the + <partial> arguments refer to the TRANSCODED and DECODED section data. + + Note that unlike the FETCH command, the CONVERT command never sets + the \Seen flag on converted messages. A client wishing to mark a + message with the \Seen flag would need to issue a STORE command + (possibly pipelined with the CONVERT request) to do that. + + The UID CONVERT command is different from the CONVERT command in the + same way as the UID FETCH command is different from the FETCH + command: + + o UID CONVERT takes as a parameter a sequence of UIDs instead of a + sequence of message numbers. + + o UID CONVERT command MUST result in the UID data item in a + corresponding CONVERTED response. + + o An EXPUNGE response MUST NOT be sent while responding to a CONVERT + command. This rule is necessary to prevent a loss of + synchronization of message sequence numbers between client and + server. Note that an EXPUNGE response MAY be sent during a UID + CONVERT command. + + + + + + + + + +Melnikov & Coates Standards Track [Page 8] + +RFC 5259 IMAP CONVERT extension July 2008 + + + Example: The client fetches body part section 3 in the message with + the message sequence number of 2 and asks to have that attachment + converted to pdf format. + + C: a001 CONVERT 2 ("APPLICATION/PDF") BINARY[3] + S: * 2 CONVERTED (TAG "a001") (BINARY[3] {2135} + <the document in .pdf format> + ) + S: a001 OK CONVERT COMPLETED + + Example: The client requests for conversion of a text/html body part + to text/plain and asks for a charset of us-ascii. The server cannot + respect the charset conversion request because there are non-us-ascii + characters in the text/html body part, so it fails the request by + returning an ERROR phrase in place of the converted data (see + Section 9). + + C: b001 CONVERT 2 ("text/plain" ("charset" "us-ascii")) BINARY[3] + S: * 2 CONVERTED (tag "b001") (BINARY[3] + (ERROR "Source text has non us-ascii" BADPARAMETERS + "text/html" "text/plain" ("charset" "us-ascii"))) + S: b001 NO All conversions failed + + If the client also specified the "unknown-character-replacement" + conversion parameter (see Section 12.1), the same example can look + like this: + + C: b001 CONVERT 2 ("text/plain" ("charset" "us-ascii" + "unknown-character-replacement" "?")) BINARY[3] + S: * 2 CONVERTED (TAG "b001") (BINARY[3] {2135} + <the document in text/plain format with us-ascii + charset> + ) + S: b001 OK CONVERT COMPLETED + + The server replaced non-us-ascii characters with a us-ascii character + such as "?". + + Example: The client first requests the converted size of a text/html + body part converted to text/plain: + + C: c000 CONVERT 2 ("TEXT/PLAIN" ("CHARSET" "us-ascii")) + BINARY.SIZE[4] + S: * 2 CONVERTED (TAG "c000") (BINARY.SIZE[4] 3135) + S: c000 OK CONVERT COMPLETED + + + + + + +Melnikov & Coates Standards Track [Page 9] + +RFC 5259 IMAP CONVERT extension July 2008 + + + Later on, the client requests 1000 bytes from the converted body + part, starting from byte 2001: + + C: c001 CONVERT 2 ("TEXT/PLAIN" ("CHARSET" "us-ascii")) + BINARY[4]<2001.1000> + S: * 2 CONVERTED (TAG "c001") (BINARY[4]<2001> {135} + <bytes 2001 - 2135 of the document in text/plain format> + ) + S: c001 OK CONVERT COMPLETED + + The server MUST respect the target MIME type and conversion + parameters specified by the client in the transcoding request. Note + that some conversion parameters can restrict what kind of conversion + is possible, while others can remove some restrictions. + + It is legal for a client to request conversion of a non-leaf body + part, for example, to request conversion of a multipart/* into a PDF + document. However, servers implementing this extension are not + required to support such conversions. Servers that support such + conversions MUST return one or more CONVERSION responses in response + to a 'CONVERSIONS "multipart/*" "*"' command. See Section 5.1 for + more details. + + The client can request header conversions using the BODY[...HEADER] + CONVERT request, for example + + C: D001 FETCH 2 BODY[HEADER] + S: * 2 FETCH (BODY[HEADER] {158} + S: Date: Mon, 20 Apr 2007 20:05:43 +0200 + S: From: Peter <peter@siroe.example.com> + S: To: Alexey <alexey@siroe.example.com> + S: Subject: =?KOI8-R?Q?why encode this?= + S: + S: ) + S: D001 OK + C: D002 CONVERT 2 (NIL ("CHARSET" "utf-8")) BODY[HEADER] + S: * 2 CONVERTED (TAG "d002") (BODY[HEADER] {157} + S: Date: Mon, 20 Apr 2007 20:05:43 +0200 + S: From: Peter <peter@siroe.example.com> + S: To: Alexey <alexey@siroe.example.com> + S: Subject: =?UTF-8?Q?why encode this?= + S: + S: ) + S: D002 OK + + Any such request MUST include the CHARSET parameter. Upon receipt of + the request, the server MUST decode any encoded words (as described + in [RFC2047]) in headers and return them re-encoded in the specified + + + +Melnikov & Coates Standards Track [Page 10] + +RFC 5259 IMAP CONVERT extension July 2008 + + + charset. (Note that encoded-words might not be needed if the result + can be represented entirely in US-ASCII, so the server MAY replace + the resulting encoded-words with their pure US-ASCII representation.) + If the server can't decode any particular encoded word, for example, + if the charset or encoding is not recognized, it MUST leave them as + is. Servers SHOULD also support decoding of any parameters as + described in [RFC2231]. Support for RFC 2231 parameters might + require reformatting of header fields during conversion. Consider + the following + + C: D011 FETCH 3 BODY[1.MIME] + S: * 3 FETCH (BODY[1.MIME] {118} + S: Content-Type: text/plain; charset=utf-8; + S: foo*0*=utf-8'fr'tr%c0; + S: foo*1*(very)=%03s_m%c0; + S: foo*2*=(nasty)%09chant + S: + S: D011 OK + + The server should preserve the headers during the conversion as much + as possible. In case the characters are split (legally!) between + fragments of an encoded parameter, the server MUST consolidate the + parameter fragments, and convert, emit, and re-fragment them as + necessary in order to keep the line length less than 78. Comments + embedded like this SHOULD be preserved during conversion, but clients + MUST gracefully handle the situation where comments are removed + entirely. If the comments are preserved, they MAY be moved after the + parameter. For example (continuing the previous example): + + C: D012 CONVERT 3 (NIL) BODY[1.MIME] + S: * 3 CONVERTED (TAG "D012") (BODY[1.MIME] {109} + S: Content-Type: text/plain; charset=utf-8; + S: foo*0*=utf-8'fr'tr%c0%03s_; + S: foo*1*=%m%c0%09chant (very)(nasty) + S: + S: D012 OK + + No destination MIME type MUST be specified with BODY[HEADER], + BODY[section.HEADER], or BODY[section.MIME]. That is, BODY[HEADER], + BODY[section.HEADER], or BODY[section.MIME] can only be used with the + "default conversion". When performing these conversions, the server + SHOULD leave encoded words as encoded words. A failure to do so may + alter the semantics of structured headers. + + + + + + + + +Melnikov & Coates Standards Track [Page 11] + +RFC 5259 IMAP CONVERT extension July 2008 + + +7. CONVERT Conversion Parameters + + The registry established by [MEDIAFEAT-REG] defines names of + conversion parameters that can be used in the CONVERT command. + Support for some conversion parameters is mandatory, as described in + Section 7.1. + + According to [MEDIAFEAT-REG], conversion parameter names are case- + insensitive. + + The following example illustrates how target picture dimensions can + be specified in a CONVERT request using the PIX-X and PIX-Y + parameters defined in [DISP-FEATURES]. + + C: e001 UID CONVERT 100 ("IMAGE/JPEG" ("PIX-X" "128" + "PIX-Y" "96")) BINARY[2] + S: * 2 CONVERTED (TAG "e001") (UID 100 BINARY[2] ~{4182} + <this part of a document is a rescaled image in + JPEG format with width=128, height=96.> + ) + S: e001 OK UID CONVERT COMPLETED + +7.1. Mandatory-to-Implement Conversions and Conversion Parameters + + A server implementing CONVERT MUST support charset conversions for + the text/plain MIME type, and MUST support charset conversions from + iso-8859-1, iso-8859-2, iso-8859-3, iso-8859-4, iso-8859-5, + iso-8859-6, iso-8859-7, iso-8859-8, and iso-8859-15 to utf-8. + + The server MUST list "text/plain" as an allowed destination + conversion from "text/plain" MIME type (see Section 5.1). A command + 'CONVERSIONS "text/plain" "text/plain"' MUST also return "charset" + and "unknown-character-replacement" (see Section 12.1) as supported + conversion parameters in the corresponding CONVERSION response. + + IMAP servers implementing the CONVERT extension MUST support + recognition of the "charset" [CHARSET-REG] parameter for text/plain, + text/html, text/css, text/csv, text/enriched, and text/xml MIME + types. Note, a server implementation is not required to support any + conversion from the text MIME subtypes specified above, except for + the mandatory-to-implement conversion described above. That is, a + server implementation MUST support the "charset" parameter for text/ + csv, only if it supports any conversion from text/csv. + + The server MUST support decoding of [RFC2047] headers and their + conversion to UTF-8 as long as the encoded words are in one of the + supported charsets. + + + + +Melnikov & Coates Standards Track [Page 12] + +RFC 5259 IMAP CONVERT extension July 2008 + + + Servers SHOULD offer additional character encoding conversions where + they make sense, as character conversion libraries are generally + available on many platforms. + + If the server cannot carry out the charset conversion while + preserving all the characters (i.e., a source character can't be + represented in the target charset), and the "unknown-character- + replacement" conversion parameter is not specified, then the server + MUST fail the conversion and MUST return the untagged ERROR + BADPARAMETERS response (see Section 9). If the value specified in + the "unknown-character-replacement" conversion itself can't be + represented in the target charset, then the server MUST also fail the + conversion and MUST return the untagged ERROR BADPARAMETERS response + (see Section 9). + +7.2. Additional Features for Mobile Usage + + This section is informative. + + Based on the expected usage of CONVERT in mobile environments, server + implementors should consider support for the following conversions: + + o Conversion of HTML and XHTML documents to text/plain in ways that + preserve at the minimum the document structure and tables. + + o Image conversions among the types image/gif, image/jpeg, and + image/png for at least the following parameters: + + * size limit (i.e., reduce quality) + + * width ("pix-x" parameter) + + * height ("pix-y" parameter) + + * resize directive (crop, stretch, aspect ratio) + + The support for "depth" may also be of interest. + + Audio conversion is also of interest but the relevant formats depend + significantly on the usage context. + + + + + + + + + + + +Melnikov & Coates Standards Track [Page 13] + +RFC 5259 IMAP CONVERT extension July 2008 + + +8. Request/Response Data Items to CONVERT/UID CONVERT Commands + +8.1. CONVERTED Untagged Response + + Contents: convert correlator + CONVERTED return data items + + The CONVERTED response may be sent as a result of a successful, + partially successful, or unsuccessful CONVERT or UID CONVERT command + specified in Section 6. + + The CONVERTED response starts with a message number, followed by the + "CONVERTED" label. The label is followed by a convert correlator, + which contains the tag of the command that caused the response to be + returned. This can be used by a client to match a CONVERTED response + against a corresponding CONVERT/UID CONVERT command. + + The convert correlator is followed by a list of one or more CONVERT + return data items. If the UID data item is returned, it MUST be + returned as the first data item in the CONVERTED response. This + requirement is to simplify client implementations. See Section 10 + and the remainder of Section 8 for more details. + +8.2. BODYPARTSTRUCTURE CONVERT Request and Response Item + + BODYPARTSTRUCTURE[section-part] + + The CONVERT extension defines the BODYPARTSTRUCTURE CONVERT data + item. Data contained in the BODYPARTSTRUCTURE return data item + follows the exact syntax specified in the [RFC3501] BODYSTRUCTURE + data item, but only contains information for the converted part. All + information contained in BODYPARTSTRUCTURE pertains to the state of + the part after it is converted, such as the converted MIME type, sub- + type, size, or charset. Note that the client can expect the returned + MIME type to match the one it requested (as the server is required to + obey the requested MIME type) and can treat mismatch as an error. + + The returned BODYPARTSTRUCTURE data MUST match the BINARY data + returned for exactly the same conversion in the same IMAP "session". + This requirement allows a client to request BODYPARTSTRUCTURE and + BINARY data in separate commands in the same IMAP session. + + If the client lists a BODYPARTSTRUCTURE data item for a section-part + before a BINARY data item for the same section-part, then, in the + CONVERTED response, the server MUST return the BODYPARTSTRUCTURE data + prior to the corresponding BINARY data. Also, any BODYSTRUCTURE data + + + + + +Melnikov & Coates Standards Track [Page 14] + +RFC 5259 IMAP CONVERT extension July 2008 + + + items MUST be after the UID data item if the UID data item is + present. Both requirements are to simplify handling of converted + data in clients. + + Example: + C: e002 CONVERT 2 (NIL ("PIX-X" "128" "PIX-Y" "96")) (BINARY[2] + BODYPARTSTRUCTURE[2]) + S: * 2 CONVERTED (TAG "e002") (BODYPARTSTRUCTURE[2] ("IMAGE" + "JPEG" () NIL NIL "8bit" 4182 NIL NIL NIL) BINARY[2] + ~{4182} + <this part of a document is a rescaled image in + JPEG format with width=128, height=96.> + ) + S: e002 OK CONVERT COMPLETED + +8.3. BINARY.SIZE CONVERT Request and Response Item + + BINARY.SIZE[section-part] + + This item requests the converted size of the section (i.e., the size + to expect in a response to the corresponding CONVERT BINARY request). + The returned value MUST be exact and MUST NOT change during a + duration of an IMAP "session", unless the message is expunged in + another session (see below). This allows a client to download a + converted part in chunks (using "<partial>"). This requirement means + that in most cases the server needs to perform conversion of the + requested body part before returning its size. + + If the message is expunged in another session, then the server MAY + return the value 0 in response to the BINARY.SIZE request item later + in the same session. + + In order to allow for upgrade of server transcoding components, + clients MUST NOT assume that repeating a particular body part + conversion in another IMAP "session" would yield the same result as a + previous conversion of the very same body part -- any characteristics + of the converted body part might be different (format, size, etc.). + In particular, clients MUST NOT cache sizes of converted messages/ + body parts beyond duration of any IMAP "session", or use sizes + obtained in one connection in another IMAP connection to the same + server. + + Historical note: Previous experience with IMAP servers that returned + estimated RFC822.SIZE value shows that this caused interoperability + problems. If the server returns a value that is smaller than the + actual size, this will result in data truncation if <partial> + + + + + +Melnikov & Coates Standards Track [Page 15] + +RFC 5259 IMAP CONVERT extension July 2008 + + + download is used. If the server returns a value that is bigger than + the actual size, this might mislead a client to believe that it + doesn't have enough storage to download a body part. + + Note for client implementors: client authors are cautioned that this + might be an expensive operation for some server implementations. + Requesting BINARY.SIZE for a large number of converted body parts or + for multiple conversions of the same body part can result in slow + performance and/or excessive server load and is discouraged. Client + implementors should consider implementation approaches that limit + this request to only the most necessary cases and are encouraged to + test the performance impact of BINARY.SIZE with multiple server + implementations. + +8.4. AVAILABLECONVERSIONS CONVERT Request and Response Item + + AVAILABLECONVERSIONS[section-part] allows the client to request the + list of target MIME types the specified body part of a message or the + whole message can be converted to. This data item is only useful + when the default conversion (see Section 6) is requested. + + This data item MUST return a list of target MIME types that is a + subset of the list returned by the CONVERSIONS command for the same + source and target MIME type pairs. If specific conversion is + requested, it MUST return the target MIME type as requested in the + CONVERT command, or the ERROR phrase. + + For both specific or default conversion requests, if conversion + parameters are specified, then the server must take them into + consideration when generating the list of target MIME types. For + example, if one or more of the conversion parameters doesn't apply to + a potential target MIME type, then such MIME type MUST be omitted + from the resulting list. If the server only had a single target MIME + type candidate and it was discarded due to the list of conversion + parameters, then the server SHOULD return the ERROR phrase instead of + the empty list of the target MIME types. + + The AVAILABLECONVERSIONS request SHOULD be processed quickly if + specified by itself. Note that if a MIME type is returned in + response to the AVAILABLECONVERSIONS, there is no guaranty that the + corresponding BINARY/BINARY.SIZE/BODYPARTSTRUCTURE CONVERT request + will not fail. + + Example: + C: f001 CONVERT 2 (NIL) (AVAILABLECONVERSIONS[2]) + S: * 2 CONVERTED (TAG "f001") (AVAILABLECONVERSIONS[2] + (("IMAGE/JPEG" "application/PostScript")) + S: f001 OK CONVERT COMPLETED + + + +Melnikov & Coates Standards Track [Page 16] + +RFC 5259 IMAP CONVERT extension July 2008 + + +8.5. Implementation Considerations + + Note that this section is normative. + + Servers MAY refuse to execute conversion requests that convert + multiple messages and/or body parts at once, e.g., a conversion + request that specifies multiple message numbers/UIDs. If the server + refuses a conversion because the request lists too many messages, the + server MUST return the MAXCONVERTMESSAGES response code (see + Section 9). For example: + + C: g001 CONVERT 1:* ("text/plain" ("charset" "us-ascii")) + BINARY[3] + S: g001 NO [MAXCONVERTMESSAGES 1] + + If the server refuses a conversion because the request lists too many + body parts, the server MUST return the MAXCONVERTPARTS response code + (see Section 9). For example: + + C: h001 CONVERT 1 ("text/plain" ("charset" "us-ascii")) + (BINARY[1] BINARY[2]) + + S: g001 NO [MAXCONVERTPARTS 1] You can only request 1 body part at + any given time + + Note for server implementors: In order to improve performance, + implementations SHOULD cache converted body parts. For example, the + server may perform a body part conversion when it receives the first + BINARY.SIZE[...], BODYPARTSTRUCTURE[...], or BINARY[...] request and + cache it until the client requests conversion/download of another + body part, a different conversion of the same body part, or until the + mailbox is closed. In order to mitigate denial-of-service attacks + from misbehaving or badly-written clients, a server SHOULD limit the + number of converted body parts it can cache. Servers SHOULD be able + to cache at least 2 conversions at any given time. + +9. Status Responses and Response Code Extensions + + A syntactically invalid MIME media type SHOULD generate a BAD tagged + response from the server. An unrecognized MIME media type generates + a NO tagged response. + + Some transcodings may require parameters. If a transcoding request + with no parameters is sent for a format which requires parameters, + the server will return an ERROR MISSINGPARAMETERS phrase in place of + the data associated with the data items requested. This is analogous + to the NIL response in FETCH, but with structured data associated + with the failure. + + + +Melnikov & Coates Standards Track [Page 17] + +RFC 5259 IMAP CONVERT extension July 2008 + + + If the server is unable to perform the requested conversion because a + resource is temporary unavailable (e.g., lack of disk space, + temporary internal error, transcoding service down), then the server + MUST return a tagged NO response that SHOULD contain the TEMPFAIL + response code (see below), or an ERROR TEMPFAIL phrase. + + If the requested conversion cannot be performed because of a + permanent error, for example, if a proprietary document format has no + existing transcoding implementation, the server MUST return a + CONVERTED response containing a ERROR BADPARAMETERS or ERROR + MISSINGPARAMETERS phrase. + + The server MAY choose to return one ERROR phrase for a single + conversion if several related data items are requested. For + instance: + + C: b002 CONVERT 2 ("text/plain" ("charset" "us-ascii")) + (BINARY[3] BODYPARTSTRUCTURE[3]) + S: * 2 CONVERTED (tag "b002") (BODYPARTSTRUCTURE[3] + (ERROR "Source text has non us-ascii" BADPARAMETERS + "text/html" "text/plain" ("charset" "us-ascii"))) + S: b002 NO All conversions failed + + If at least one conversion succeeds, the server MUST return an OK + response. If all conversions fail, the server MAY return OK or NO. + For instance: + + C: b002 CONVERT 2 ("text/plain" ("charset" "us-ascii")) + (BINARY[3] BODYPARTSTRUCTURE[3] BINARY[4] + BODYPARTSTRUCTURE[4]) + S: * 2 CONVERTED (tag "b002") (BODYPARTSTRUCTURE[3] + (ERROR "Source text has non us-ascii" BADPARAMETERS + "text/html" "text/plain" ("charset" "us-ascii")) + BODYSTRUCTURE[4] ("TEXT" "PLAIN" (CHARSET US-ASCII) + NIL NIL "8bit" 4182 NIL NIL NIL) BINARY[4] {4182} + <body in text plain> + ) + S: b002 OK Some conversions failed + + In general, the client can tell from the BODYPARTSTRUCTURE response + whether or not its request was honored exactly, but may not know the + reasons why. + + This document defines the following response codes that can be + returned in the tagged NO response code. + + TEMPFAIL - The transcoding request failed temporarily. It might + succeed later, so the client MAY retry. + + + +Melnikov & Coates Standards Track [Page 18] + +RFC 5259 IMAP CONVERT extension July 2008 + + + MAXCONVERTMESSAGES <number> - The server is unable or unwilling to + convert more than <number> messages in any given CONVERT/UID + CONVERT request. + + MAXCONVERTPARTS <number> - The server is unable or unwilling to + convert more than <number> body parts of a message at once in + any given CONVERT/UID CONVERT request. + + The word ERROR is always followed by an informal human-readable + descriptive text, which is followed by the convert-error-code. The + convert-error-code MUST be one of the following: + + TEMPFAIL mm - The transcoding request failed temporarily. It might + succeed later, so the client MAY retry. The client SHOULD wait + for at least mm minutes before retrying. + + BADPARAMETERS from-concrete-mime-type to-mime-type + "(" transcoding-params ")" - + The listed parameters were not understood, not valid for the + source/destination MIME type pair, had invalid values or could + not be honored for another reason noted in the human-readable + text that was specified after the ERROR label. The + transcoding-params can be omitted, in which case, it means that + the conversion from the from-concrete-mime-type to the to-mime- + type is not possible. If the from-concrete-mime-type is NIL, + this means that the specified body part doesn't exist. All + unrecognized or irrelevant parameters MUST be listed in the + transcoding-params. It is not legal behavior to ignore + irrelevant parameters. + + Note that if the client requested the "default conversion" (see + Section 6), the to-mime-type contains the destination MIME type + chosen by the server. + + MISSINGPARAMETERS from-concrete-mime-type to-mime-type + "(" transcoding-params ")" - + The listed parameters are required for conversion of the + specified source MIME type to the destination MIME type, but + were not seen in the request. Note that if the client + requested the "default conversion" (see Section 6), the to- + mime-type contains the destination MIME type chosen by the + server. + + + + + + + + + +Melnikov & Coates Standards Track [Page 19] + +RFC 5259 IMAP CONVERT extension July 2008 + + + Examples: + + C: b002 CONVERT 2 ("APPLICATION/PDF") BINARY[3] + S: b002 NO [TEMPFAIL] All conversions failed + + C: b003 CONVERT 2 ("TEXT/PLAIN") BINARY[3] + S: * 2 CONVERTED (tag "b003") (BINARY[3] + (ERROR "CHARSET must be specified for text conversions" + MISSINGPARAMETERS (CHARSET))) + S: b003 NO All conversions failed + + C: b005 CONVERT 2 ("TEXT/PLAIN" (CHARSET "US-ASCII" + UNKNOWN-CHARACTER-REPLACEMENT "<badchar>")) BINARY[3] + S: * 2 CONVERTED (tag "b005") (BINARY[3] + (ERROR "UNKNOWN-CHARACTER-REPLACEMENT limited to 4 + bytes" BADPARAMETERS (UNKNOWN-CHARACTER-REPLACEMENT + "<badchar>"))) + S: b005 NO All conversions failed + +10. Formal Syntax + + The following syntax specification uses the augmented Backus-Naur + Form (ABNF) notation as used in [ABNF], and incorporates by reference + the core rules defined in that document. + + This syntax augments the grammar specified in [RFC3501] and + [RFC3516]. Non-terminals not defined in this document can be found + in [RFC3501], [RFC3516], [IMAPABNF], [MIME-MTSRP], and + [MEDIAFEAT-REG]. + + command-select =/ convert + + uid =/ "UID" SP convert + ; Unique identifiers used instead of message + ; sequence numbers + + convert = "CONVERT" SP sequence-set SP convert-params SP + ( convert-att / + "(" convert-att *(SP convert-att) ")" ) + + convert-att = "UID" / + "BODYPARTSTRUCTURE" section-convert / + "BINARY" section-convert [partial] / + "BINARY.SIZE" section-convert / + "BODY[HEADER]" / + "BODY[" section-part ".HEADER]" / + "BODY[" section-part ".MIME]" / + "AVAILABLECONVERSIONS" section-convert + + + +Melnikov & Coates Standards Track [Page 20] + +RFC 5259 IMAP CONVERT extension July 2008 + + + ; <partial> is defined in [RFC3516]. + ; <section-part> is defined in [RFC3501]. + + convert-params = "(" (quoted-to-mime-type / default-conversion) + [SP "(" transcoding-params ")"] ")" + + quoted-to-mime-type = DQUOTE to-mime-type DQUOTE + + transcoding-params = transcoding-param + *(SP transcoding-param) + + transcoding-param-names = transcoding-param-name + *(SP transcoding-param-name) + + transcoding-param = transcoding-param-name SP + transcoding-param-value + + transcoding-param-name = astring + ; <transcod-param-name-nq> represented as a quoted, + ; literal or atom. Note that + ; <transcod-param-name-nq> allows for "%", which is + ; not allowed in atoms. Such values must be + ; represented as quoted or literal. + + transcod-param-name-nq = Feature-tag + ; <Feature-tag> is defined in [MEDIAFEAT-REG]. + + transcoding-param-value = astring + + default-conversion = "NIL" + + message-data =/ nz-number SP "CONVERTED" SP convert-correlator + SP convert-msg-attrs + + convert-correlator = "(" "TAG" SP tag-string ")" + + tag-string = string + ; tag of the command that caused + ; the CONVERTED response, sent as + ; a string. + + convert-msg-attrs = "(" convert-msg-att *(SP convert-msg-att) ")" + ; "UID" MUST be the first data item, if present. + + convert-msg-att = msg-att-semistat / msg-att-conv-static + + msg-att-conv-static = "UID" SP uniqueid + ; MUST NOT change for a message + + + +Melnikov & Coates Standards Track [Page 21] + +RFC 5259 IMAP CONVERT extension July 2008 + + + msg-att-semistat = + ( "BINARY" section-convert ["<" number ">"] SP + (nstring / literal8 / converterror-phrase) ) / + ( "BINARY.SIZE" section-convert SP + (number / converterror-phrase) ) / + ( "BODYPARTSTRUCTURE" section-convert SP + (body / converterror-phrase) ) / + ( "AVAILABLECONVERSIONS" section-convert SP + (mimetype-list / converterror-phrase) ) + ; MUST NOT change during an IMAP "session", + ; but not necessarily static in the long term. + + section-convert = section-binary + ; <section-binary> is defined in [RFC3516]. + ; + ; Note that unlike [RFC3516], conversion + ; of a top level multipart/* is allowed. + + resp-text-code =/ "TEMPFAIL" / + "MAXCONVERTMESSAGES" SP nz-number / + "MAXCONVERTPARTS" SP nz-number + ; <resp-text-code> is defined in [RFC3501]. + + mimetype-and-params = quoted-to-mime-type + [SP "(" transcoding-params ")"] + ; always includes a specific MIME type + + mimetype-list = "(" "(" [quoted-to-mime-type + *(SP quoted-to-mime-type)] ")" ")" + ; Unordered list of MIME types. It can be empty. + ; + ; Two levels of parenthesis is needed to distinguish this + ; data from <converterror-phrase>. + + converterror-phrase = "(" "ERROR" SP + convert-err-descript SP convert-error-code ")" + + convert-error-code = "TEMPFAIL" [SP nz-number] + / bad-params + / missing-params + + convert-err-descript = string + ; Human-readable text explaining the conversion error. + ; The default charset is US-ASCII, unless + ; the LANGUAGE command [IMAP-I18N] is called, when + ; the charset changes to UTF-8. + + quoted-from-mime-type = DQUOTE from-concrete-mime-type DQUOTE + + + +Melnikov & Coates Standards Track [Page 22] + +RFC 5259 IMAP CONVERT extension July 2008 + + + bad-params = "BADPARAMETERS" + 1*(SP (quoted-from-mime-type / nil) + SP mimetype-and-params) + ; nil is only returned when the body part doesn't exist. + + missing-params = "MISSINGPARAMETERS" + 1*(SP quoted-from-mime-type SP + mimetype-and-missing-params) + + mimetype-and-missing-params = quoted-to-mime-type + "(" transcoding-param-names ")" + ; always includes a specific MIME type + + concrete-mime-type = type-name "/" subtype-name + ; i.e., "type/subtype". + ; type-name and subtype-name + ; are defined in [MIME-MTSRP]. + + from-concrete-mime-type = concrete-mime-type + + to-mime-type = concrete-mime-type + + command-auth =/ conversions-cmd + + conversions-cmd = "CONVERSIONS" SP from-mime-type-req SP + to-mime-type-req + + from-mime-type-req = astring + ; "mime-type-req" represented as IMAP <atom>, + ; <quoted> or <literal> + + to-mime-type-req = astring + ; <mime-type-req> represented as IMAP <atom>, + ; <quoted> or <literal>. + ; Note that <mime-type-req> allows for "*", + ; which is not allowed in <atom>. Such values must + ; be represented as <quoted> or <literal>. + + any-mime-type = "*" + + mime-type-req = any-mime-type / + (type-name "/" any-mime-type) / + concrete-mime-type + ; '*', 'type/*' or 'type/subtype'. + ; type-name is defined in [MIME-MTSRP]. + + response-payload =/ conversion-data + + + + +Melnikov & Coates Standards Track [Page 23] + +RFC 5259 IMAP CONVERT extension July 2008 + + + conversion-data = "CONVERSION" SP quoted-from-mime-type SP + quoted-to-mime-type + [SP "(" transcoding-param-name + *(SP transcoding-param-name) ")"] + +11. Manageability Considerations + + The monitoring of CONVERT operation is similar to monitoring of the + IMAP FETCH operation. + + At the time of writing this document, there is no standard IMAP MIB + defined. Similarly, a standard MIB for monitoring CONVERT operations + and their failures does not exist. However, the authors believe that + in the absence of such a MIB, server implementations SHOULD provide + operators with tools to report the following information: + + o which conversions (source and target MIME types and possibly + conversion parameters used) are invoked more frequently and how + long they take, + + o information about conversion errors and which error condition + caused them (see Section 9), and + + o information about users which invoke conversion operation. + + This information can help operators to detect client abuse of this + extension and scalability issues that might arise from its use. + + Standardizing these tools may be the subject of future work. + +12. IANA Considerations + + IMAP4 capabilities are registered by publishing a Standards Track or + IESG-approved Experimental RFC. This document defines the CONVERT + IMAP capability. IANA has added this extension to the IANA IMAP + Capability registry. + + IANA has performed registrations as defined in the following + subsections. + + + + + + + + + + + + +Melnikov & Coates Standards Track [Page 24] + +RFC 5259 IMAP CONVERT extension July 2008 + + +12.1. Registration of unknown-character-replacement Media Type + Parameter + + IANA has added the following registration to the registry established + by RFC 2506. + + To: "Media feature tags mailing list" + <media-feature-tags@apps.ietf.org> + + Subject: Registration of media feature tag + unknown-character-replacement + + Media feature tag name: + unknown-character-replacement + + ASN.1 identifier associated with feature tag: + 1.3.6.1.8.1.33 + + Summary of the media feature indicated by this feature tag: + Allows servers that can perform charset conversion for text/plain + text/html, text/css, text/csv, text/enriched, and text/xml MIME + types to replace characters not supported by the target charset + with a fixed string, such as "?". + This feature tag is also applicable to other conversions + to text, e.g., conversion of images using OCR (optical + character recognition). + + Values appropriate for use with this feature tag: + The feature tag contains a UTF-8 string used to replace any + characters from the source media type that can't be + represented in the target media type. + + The feature tag is intended primarily for use in the following + applications, protocols, services, or negotiation mechanisms: + IMAP CONVERT extension [RFC5259] + + Examples of typical use: + C: b001 CONVERT 2 BINARY[3 ("text/plain" ("charset" + "us-ascii" "unknown-character-replacement" "?"))] + + Related standards or documents: + [RFC5259] + [CHARSET-REG] + + Considerations particular to use in individual applications, + protocols, services, or negotiation mechanisms: + None + + + + +Melnikov & Coates Standards Track [Page 25] + +RFC 5259 IMAP CONVERT extension July 2008 + + + Interoperability considerations: None + + Security considerations: None + + Additional information: + This media feature only make sense for MIME types that + also support the "charset" media type parameter + [CHARSET-REG]. + + Name(s) & email address(es) of person(s) to contact for further + information: + Alexey Melnikov <alexey.melnikov@isode.com> + + Intended usage: + COMMON + + Author/Change controller: + IETF + + Requested IANA publication delay: + None + + Other information: + None + +13. Security Considerations + + It is to be noted that some conversions may present security threats + (e.g., converting a document to a damaging executable, exploiting a + buffer overflow in a media codec/parser, or a denial-of-service + attack against a client or a server such as requesting an image be + scaled to extremely large dimensions). Server SHOULD refuse to + execute CPU-expensive conversions. Servers should avoid dangerous + conversions if possible. Whenever possible, servers should perform + verification of the converted attachments before returning them to + the client. Clients should be careful when requesting conversions or + processing transformed attachments. Clients SHOULD use mutual Simple + Authentication and Security Layer (SASL) authentication and the SASL/ + TLS integrity layer, to make sure they are talking to trusted + servers. + + When the client requests a server-side conversion of a signed body + part (e.g., a part inside multipart/signed), there is no way for the + client to verify that the converted content is authentic. A client + not trusting the server to perform conversion of a signed body part + can download the signed object, verify the signature, and perform the + conversion itself. + + + + +Melnikov & Coates Standards Track [Page 26] + +RFC 5259 IMAP CONVERT extension July 2008 + + + A client can create a carefully crafted bad message with the APPEND + command followed by the CONVERT command to attack the server. If the + server's conversion function or library has a security problem (such + as vulnerability to a buffer overflow), this could result in + privilege escalation or denial of service. In order to mitigate such + attacks, servers SHOULD log the client authentication identity on + APPEND and/or CONVERT operations in order to facilitate tracking of + abusive clients. Also server implementors SHOULD isolate the + conversion function or library from the privileged mailstore, perhaps + by running it within a distinct process. + + Deployments in which the actual transcoding is done outside the IMAP + server in a separate server are recommended to keep the servers in + the same trusted domain (e.g., subnet). + +14. Acknowledgments + + Stephane H. Maes and Ray Cromwell from Oracle edited several earlier + versions of this document. Their contribution is gratefully + acknowledged. + + The authors want to specifically acknowledge the excellent criticism + and comments received from Randall Gellens (Qualcomm), Arnt + Gulbrandsen (Oryx), Zoltan Ordogh (Nokia), Ben Last (Emccsoft), Dan + Karp (Zimbra), Pete Resnick (Qualcomm), Chris Newman (Sun), Ted + Hardie (Qualcomm), Larry Masinter (Adobe), Philip Guenther + (Sendmail), Greg Vaudreuil (Alcatel-Lucent), David Harrington + (Comcast), Dave Cridland (Isode), Pasi Eronen (Nokia), Magnus + Westerlund (Ericsson), and Jari Arkko (Ericsson), which improved the + quality of this specification considerably. + + The authors would also like to specially thank Dave Cridland for the + MEDIACAPS command proposal and Dan Karp for the CONVERSIONS command + proposal. + + The authors also want to thank all who have contributed key insight + and extensively reviewed and discussed the concepts of CONVERT and + its predecessor P-IMAP. In particular, this includes the authors of + the LCONVERT document: Rafiul Ahad (Oracle Corporation), Eugene Chiu + (Oracle Corporation), Ray Cromwell (Oracle Corporation), Jia-der Day + (Oracle Corporation), Vi Ha (Oracle Corporation), Wook-Hyun Jeong + (Samsung Electronics Co. LTF), Chang Kuang (Oracle Corporation), + Rodrigo Lima (Oracle Corporation), Stephane H. Maes (Oracle + Corporation), Gustaf Rosell (Sony Ericsson), Jean Sini (Symbol + Technologies), Sung-Mu Son (LG Electronics), Fan Xiaohui (China + Mobile Communications Corporation (CMCC)), and Zhao Lijun (China + Mobile Communications Corporation (CMCC)). + + + + +Melnikov & Coates Standards Track [Page 27] + +RFC 5259 IMAP CONVERT extension July 2008 + + +15. References + +15.1. Normative References + + [ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", STD 68, RFC 5234, + January 2008. + + [CHARSET-REG] Hoffman, P., "Registration of Charset and Languages + Media Features Tags", RFC 2987, November 2000. + + [IMAPABNF] Melnikov, A. and C. Daboo, "Collected Extensions to + IMAP4 ABNF", RFC 4466, April 2006. + + [MEDIAFEAT-REG] Holtman, K., Mutz, A., and T. Hardie, "Media Feature + Tag Registration Procedure", BCP 31, RFC 2506, + March 1999. + + [MIME-MTSRP] Freed, N. and J. Klensin, "Media Type Specifications + and Registration Procedures", BCP 13, RFC 4288, + December 2005. + + [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail + Extensions) Part Three: Message Header Extensions + for Non-ASCII Text", RFC 2047, November 1996. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and + Encoded Word Extensions: + Character Sets, Languages, and Continuations", + RFC 2231, November 1997. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - + VERSION 4rev1", RFC 3501, March 2003. + + [RFC3516] Nerenberg, L., "IMAP4 Binary Content Extension", + RFC 3516, April 2003. + + + + + + + + + + + + +Melnikov & Coates Standards Track [Page 28] + +RFC 5259 IMAP CONVERT extension July 2008 + + +15.2. Informative References + + [DISP-FEATURES] Masinter, L., Wing, D., Mutz, A., and K. Holtman, + "Media Features for Display, Print, and Fax", + RFC 2534, March 1999. + + [IMAP-I18N] Newman, C., Gulbrandsen, A., and A. Melnikov, + "Internet Message Access Protocol + Internationalization", RFC 5255, June 2008. + + [LEM-STREAMING] Cook, N., "Streaming Internet Messaging + Attachments", Work in Progress, June 2008. + + [OMA-ME-RD] OMA, "Open Mobile Alliance Mobile Email Requirement + Document", OMA 55.919 3.0.0, December 2007. + + [OMA-STI] OMA, "Open Mobile Alliance, Standard Transcoding + Interface Specification", OMA OMA-STI-V1_0, + December 2005. + +Authors' Addresses + + Alexey Melnikov (editor) + Isode Ltd + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: Alexey.Melnikov@isode.com + + + Peter Coates (editor) + Sun Microsystems + 185 Falcon Drive + Whitehorse, YT Y1A 6T2 + Canada + + EMail: peter.coates@Sun.COM + + + + + + + + + + + + +Melnikov & Coates Standards Track [Page 29] + +RFC 5259 IMAP CONVERT extension July 2008 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2008). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Melnikov & Coates Standards Track [Page 30] + diff --git a/imap/docs/rfc/rfc5267.txt b/imap/docs/rfc/rfc5267.txt new file mode 100644 index 00000000..91bfa223 --- /dev/null +++ b/imap/docs/rfc/rfc5267.txt @@ -0,0 +1,1011 @@ + + + + + + +Network Working Group D. Cridland +Request for Comments: 5267 C. King +Category: Standards Track Isode Limited + July 2008 + + + Contexts for IMAP4 + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + The IMAP4rev1 protocol has powerful search facilities as part of the + core protocol, but lacks the ability to create live, updated results + that can be easily handled. This memo provides such an extension, + and shows how it can be used to provide a facility similar to virtual + mailboxes. + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Cridland & King Standards Track [Page 1] + +RFC 5267 IMAP CONTEXT July 2008 + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 + 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 + 3. Extended Sort Syntax . . . . . . . . . . . . . . . . . . . . . 3 + 3.1. ESORT Extension . . . . . . . . . . . . . . . . . . . . . 4 + 3.2. Ranges in Extended Sort Results . . . . . . . . . . . . . 4 + 3.3. Extended SORT Example . . . . . . . . . . . . . . . . . . 4 + 4. Contexts . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 4.2. Context Hint . . . . . . . . . . . . . . . . . . . . . . . 5 + 4.3. Notifications of Changes . . . . . . . . . . . . . . . . . 6 + 4.3.1. Refusing to Update Contexts . . . . . . . . . . . . . 7 + 4.3.2. Common Features of ADDTO and REMOVEFROM . . . . . . . 8 + 4.3.3. ADDTO Return Data Item . . . . . . . . . . . . . . . . 8 + 4.3.4. REMOVEFROM Return Data Item . . . . . . . . . . . . . 9 + 4.3.5. The CANCELUPDATE Command . . . . . . . . . . . . . . . 10 + 4.4. Partial Results . . . . . . . . . . . . . . . . . . . . . 10 + 4.5. Caching Results . . . . . . . . . . . . . . . . . . . . . 11 + 5. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 12 + 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 + 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 + 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 + 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 + 9.1. Normative References . . . . . . . . . . . . . . . . . . . 14 + 9.2. Informative References . . . . . . . . . . . . . . . . . . 14 + Appendix A. Cookbook . . . . . . . . . . . . . . . . . . . . . . 15 + A.1. Virtual Mailboxes . . . . . . . . . . . . . . . . . . . . 15 + A.2. Trash Mailboxes . . . . . . . . . . . . . . . . . . . . . 15 + A.3. Immediate EXPUNGE Notifications . . . . . . . . . . . . . 15 + A.4. Monitoring Counts . . . . . . . . . . . . . . . . . . . . 15 + A.5. Resynchronizing Contexts . . . . . . . . . . . . . . . . . 16 + Appendix B. Server Implementation Notes . . . . . . . . . . . . . 16 + + + + + + + + + + + + + + + + + + +Cridland & King Standards Track [Page 2] + +RFC 5267 IMAP CONTEXT July 2008 + + +1. Introduction + + Although the basic SEARCH command defined in [IMAP], and as enhanced + by [ESEARCH], is relatively compact in its representation, this + reduction saves only a certain amount of data, and huge mailboxes + might overwhelm the storage available for results on even relatively + high-end desktop machines. + + The SORT command defined in [SORT] provides useful features, but is + hard to use effectively on changing mailboxes over low-bandwidth + connections. + + This memo borrows concepts from [ACAP], such as providing a windowed + view onto search or sort results, and making updates that are + bandwidth and round-trip efficient. These are provided by two + extensions: "ESORT" and "CONTEXT". + +2. Conventions Used in This Document + + In examples, "C:" and "S:" indicate lines sent by the client + messaging user agent and IMAP4rev1 ([IMAP]) server, respectively. + "//" indicates inline comments not part of the protocol exchange. + Line breaks are liberally inserted for clarity. Examples are + intended to be read in order, such that the state remains from one + example to the next. + + Although the examples show a server that supports [ESEARCH], this is + not a strict requirement of this specification. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [KEYWORDS]. + + Other capitalized words are typically names of IMAP extensions or + commands -- these are uppercased for clarity only, and are case- + insensitive. + +3. Extended Sort Syntax + + Servers implementing the extended SORT provide a suite of extensions + to the SORT and UID SORT commands defined in [SORT]. This allows for + return options, as used with SEARCH and specified in [IMAP-ABNF], to + be used with SORT in a similar manner. + + The SORT and UID SORT commands are extended by the addition of an + optional list of return options that follow a RETURN atom immediately + after the command. If this is missing, the server will return + results as specified in [SORT]. + + + +Cridland & King Standards Track [Page 3] + +RFC 5267 IMAP CONTEXT July 2008 + + + The extended SORT command always returns results in the requested + sort order, but is otherwise identical in its behaviour to the + extended SEARCH command defined in [IMAP-ABNF], as extended by + [ESEARCH]. In particular, the extended SORT command returns results + in an ESEARCH response. + +3.1. ESORT Extension + + Servers advertising the capability "ESORT" support the return options + specified in [ESEARCH] in the SORT command. These return options are + adapted as follows: + + MIN + Return the message number/UID of the lowest sorted message + satisfying the search criteria. + + MAX + Return the message number/UID of the highest sorted message + satisfying the search criteria. + + ALL + Return all message numbers/UIDs which match the search criteria, + in the requested sort order, using a sequence-set. Note the use + of ranges described below in Section 3.2. + + COUNT + As in [ESEARCH]. + +3.2. Ranges in Extended Sort Results + + Any ranges given by the server, including those given as part of the + sequence-set, in an ESEARCH response resulting from an extended SORT + or UID SORT command, MUST be ordered in increasing numerical order + after expansion, as per usual [IMAP] rules. + + In particular this means that 10:12 is equivalent to 12:10, and + 10,11,12. To avoid confusion, servers SHOULD present ranges only + when the first seq-number is lower than the second; that is, either + of the forms 10:12 or 10,11,12 is acceptable, but 12:10 SHOULD be + avoided. + +3.3. Extended SORT Example + + If the list of return options is present but empty, then the server + provides the ALL return data item in an ESEARCH response. This is + functionally equivalent to an unextended UID SORT command, but can + use a smaller representation: + + + + +Cridland & King Standards Track [Page 4] + +RFC 5267 IMAP CONTEXT July 2008 + + + C: E01 UID SORT RETURN () (REVERSE DATE) UTF-8 UNDELETED + UNKEYWORD $Junk + S: * ESEARCH (TAG "E01") UID ALL 23765,23764,23763,23761,[...] + S: E01 OK Sort completed + + Note that the initial three results are not represented as the range + 23765:23763 as mandated in Section 3.2. + +4. Contexts + +4.1. Overview + + The Contexts extension is present in any IMAP4rev1 server that + includes the string "CONTEXT=SEARCH", and/or "CONTEXT=SORT", within + its advertised capabilities. + + In the case of CONTEXT=SEARCH, the server supports the extended + SEARCH command syntax described in [IMAP-ABNF], and accepts three + additional return options. + + Servers advertising CONTEXT=SORT also advertise the SORT capability, + as described in [SORT], support the extended SORT command syntax + described in Section 3, and accept three additional return options + for this extended SORT. + + These additional return options allow for notifications of changes to + the results of SEARCH or SORT commands, and also allow for access to + partial results. + + A server advertising the CONTEXT=SEARCH extension will order all + SEARCH results, whether from a UID SEARCH or SEARCH command, in + mailbox order -- that is, by message number and UID. Therefore, the + UID SEARCH, SEARCH, UID SORT, or SORT command used -- collectively + known as the searching command -- will always have an order, the + requested order, which will be the mailbox order for UID SEARCH and + SEARCH commands. + + All of the return specifiers have no interaction with either each + other or any return specifiers defined in [ESEARCH] or Section 3.1; + however, it is believed that implementations supporting CONTEXT will + also support ESEARCH and ESORT. + +4.2. Context Hint + + The return option CONTEXT SHOULD be used by a client to indicate that + subsequent use of the search criteria are likely. Servers MAY ignore + this return option or use it as a hint to maintain a full result + cache, or index. + + + +Cridland & King Standards Track [Page 5] + +RFC 5267 IMAP CONTEXT July 2008 + + + A client might choose to obtain a count of matching messages prior to + obtaining actual results. Here, the client signals its intention to + fetch the results themselves: + + C: A01 SEARCH RETURN (CONTEXT COUNT) UNDELETED + UNKEYWORD $Junk + S: * ESEARCH (TAG "A01") COUNT 23765 + S: A01 OK Search completed. + +4.3. Notifications of Changes + + The search return option UPDATE, if used by a client, causes the + server to issue unsolicited notifications containing updates to the + results that would be returned by an unmodified searching command. + These update sets are carried in ADDTO and REMOVEFROM data items in + ESEARCH responses. + + These ESEARCH responses carry a search correlator of the searching + command, hence clients MUST NOT reuse tags, as already specified in + Section 2.2.1 of [IMAP]. An attempt to use UPDATE where a tag is + already in use with a previous searching command that itself used + UPDATE SHALL result in the server rejecting the searching command + with a BAD response. + + Both ADDTO and REMOVEFROM data items SHOULD be delivered to clients + in a timely manner, as and when results change, whether by new + messages arriving in the mailbox, metadata such as flags being + changed, or messages being expunged. + + Typically, this would occur at the same time as the FETCH, EXISTS, or + EXPUNGE responses carrying the source of the change. + + Updates will cease when the mailbox is no longer selected, or when + the CANCELUPDATE command, defined in Section 4.3.5, is issued by the + client, whichever is sooner. + + Unlike [ACAP], there is no requirement that a context need be created + with CONTEXT to use UPDATE, and in addition, the lack of UPDATE with + a CONTEXT does not affect the results caused by later searching + commands -- there is no snapshot facility. + + There is no interaction between UPDATE and any other return options; + therefore, use of RETURN (UPDATE MIN), for example, does not notify + about the minimum UID or sequence number, but notifies instead about + all changes to the set of matching messages. In particular, this + means that a client using UPDATE and PARTIAL on the same search + program could receive notifications about messages that do not + currently interest it. + + + +Cridland & King Standards Track [Page 6] + +RFC 5267 IMAP CONTEXT July 2008 + + + Finally, as specified in the errata to [IMAP], any message sequence + numbers used in the search program are evaluated at the time the + command is received; therefore, if the messages referred to by such + message sequence numbers change, no notifications will be emitted. + + This time, the client will require notifications of updates and + chooses to obtain a count: + + C: B01 UID SEARCH RETURN (UPDATE COUNT) DELETED + KEYWORD $Junk + S: * ESEARCH (TAG "B01") COUNT 74 + S: B01 OK Search completed, will notify. + // Note that the following is rejected, and has no effect: + C: B01 SORT RETURN (UPDATE) FLAGGED + S: B01 BAD Tag reuse + +4.3.1. Refusing to Update Contexts + + In some cases, the server MAY refuse to provide updates, such as if + an internal limit on the number of update contexts is reached. In + such a case, an untagged NO is generated during processing of the + command with a response-code of NOUPDATE. The response-code + contains, as argument, the tag of the search command for which the + server is refusing to honour the UPDATE request. + + Other return options specified SHALL still be honoured. + + Servers MUST provide at least one updating context per client, and + SHOULD provide more -- see Appendix B for strategies on reducing the + impact of additional updating contexts. Since sorted contexts + require a higher implementation cost than unsorted contexts, refusal + to provide updates for a SORT command does not imply that SEARCH + contexts will also be refused. + + This time, the client will require notifications of updates, and + chooses to obtain a count: + + C: B02 UID SORT RETURN (UPDATE COUNT) UTF-8 + KEYWORD $Junk + S: * ESEARCH (TAG "B02") COUNT 74 + S: * NO [NOUPDATE "B02"] Too many contexts + S: B02 OK Search completed, will not notify. + + Client handling might be to retry with a UID SEARCH command, or else + cancel an existing context; see Section 4.3.5. + + + + + + +Cridland & King Standards Track [Page 7] + +RFC 5267 IMAP CONTEXT July 2008 + + +4.3.2. Common Features of ADDTO and REMOVEFROM + + The result update set included in the return data item is specified + as UIDs or message numbers, depending on how the UPDATE was + specified. If the UPDATE was present in a SEARCH or SORT command, + the results will be message numbers; in a UID SEARCH or UID SORT + command, they will be UIDs. + + The client MUST process ADDTO and REMOVEFROM return data items in the + order they appear, including those within a single ESEARCH response. + Correspondingly, servers MUST generate ADDTO and REMOVEFROM responses + such that the results are maintained in the requested order. + + As with any response aside from EXPUNGE, ESEARCH responses carrying + ADDTO and/or REMOVEFROM return data items MAY be sent at any time. + In particular, servers MAY send such responses when no command is in + progress, during the processing of any command, or when the client is + using the IDLE facility described in [IDLE]. Implementors are + recommended to read [NOTIFY] as a mechanism for clients to signal + servers that they are willing to process responses at any time, and + are also recommended to pay close attention to Section 5.3 of [IMAP]. + + It is anticipated that typical server implementations will emit ADDTO + when they normally emit the causal FETCH or EXISTS, and similarly + emit REMOVEFROM when they normally emit the causal FETCH or EXPUNGE. + +4.3.3. ADDTO Return Data Item + + The ADDTO return data item contains, as payload, a list containing + pairs of a context position and a set of result updates in the + requested order to be inserted at the context position. Where the + searching command is a SEARCH or UID SEARCH command, the context + position MAY be zero. Each pair is processed in the order that it + appears. + + Note that an ADDTO containing message sequence numbers added as a + result of those messages being delivered or appended MUST be sent + after the EXISTS notification itself, in order that those sequence + numbers are valid. + + If the context position is non-zero, the result update is inserted at + the given context position, meaning that the first result in the set + will occupy the new context position after insertion, and any prior + existing result at that context position will be shifted to a later + context position. + + + + + + +Cridland & King Standards Track [Page 8] + +RFC 5267 IMAP CONTEXT July 2008 + + + Where the context position is zero, the client MAY insert the message + numbers or UIDs in the result list such that the result list is + maintained in mailbox order. In this case, servers are RECOMMENDED + to order the result update into mailbox order to produce the shortest + representation in set-syntax. + + [...] + S: * 23762 FETCH (FLAGS (\Deleted \Seen)) + S: * 23763 FETCH (FLAGS ($Junk \Seen)) + S: * ESEARCH (TAG "B01") UID ADDTO (0 32768:32769) + + Note that this example assumes messages 23762 and 23763 with UIDs + 32768 and 32769 (respectively) previously had neither \Deleted nor + $Junk set. Also note that only the ADDTO is included, and not the + (now changed) COUNT. + + If the searching command "C01" initially generated a result list of + 2734:2735, then the following three responses are equivalent, and + yield a result list of 2731:2735: + + [...] + S: * ESEARCH (TAG "C01") UID ADDTO (1 2733 1 2732 1 2731) + S: * ESEARCH (TAG "C01") UID ADDTO (1 2733) ADDTO (1 2731:2732) + S: * ESEARCH (TAG "C01") UID ADDTO (1 2731:2733) + + The last is the preferred representation. + +4.3.4. REMOVEFROM Return Data Item + + The REMOVEFROM return data item contains, as payload, a list + containing pairs of a context position and a set of result updates in + the requested order to be removed starting from the context position. + Where the searching command is a SEARCH or UID SEARCH command, the + context position MAY be zero. Each pair is processed in the order + that it appears. + + If the context position is non-zero, the results are removed at the + given context position, meaning that the first result in the set will + occupy the given context position before removal, and any prior + existing result at that context position will be shifted to an + earlier context position. + + Where the context position is zero, the client removes the message + numbers or UIDs in the result list wherever they occur, and servers + are RECOMMENDED to order the result list in mailbox order to obtain + the best benefit from the set-syntax. + + + + + +Cridland & King Standards Track [Page 9] + +RFC 5267 IMAP CONTEXT July 2008 + + + Note that a REMOVEFROM containing message sequence numbers removed as + a result of those messages being expunged MUST be sent prior to the + expunge notification itself, in order that those sequence numbers + remain valid. + + Here, a message in the result list is expunged. The REMOVEFROM is + shown to happen without any command in progress; see Section 4.3.2. + Note that EXPUNGE responses do not have this property. + + [...] + S: * ESEARCH (TAG "B01") UID REMOVEFROM (0 32768) + C: B03 NOOP + S: * 23762 EXPUNGE + S: B03 OK Nothing done. + +4.3.5. The CANCELUPDATE Command + + When a client no longer wishes to receive updates, it may issue the + CANCELUPDATE command, which will prevent all updates to the contexts + named in the arguments from being transmitted by the server. The + command takes, as arguments, one or more tags of the commands used to + request updates. + + The server MAY free any resource associated with a context so + disabled -- however, the client is free to issue further searching + commands with the same criteria and requested order, including + PARTIAL requests. + + C: B04 CANCELUPDATE "B01" + S: B04 OK No further updates. + +4.4. Partial Results + + The PARTIAL search return option causes the server to provide in an + ESEARCH response a subset of the results denoted by the sequence + range given as the mandatory argument. The first result is 1; thus, + the first 500 results would be obtained by a return option of + "PARTIAL 1:500", and the second 500 by "PARTIAL 501:1000". This + intentionally mirrors message sequence numbers. + + A single command MUST NOT contain more than one PARTIAL or ALL search + return option -- that is, either one PARTIAL, one ALL, or neither + PARTIAL nor ALL is allowed. + + For SEARCH results, the entire result list MUST be ordered in mailbox + order, that is, in UID or message sequence number order. + + + + + +Cridland & King Standards Track [Page 10] + +RFC 5267 IMAP CONTEXT July 2008 + + + Where a PARTIAL search return option references results that do not + exist, by using a range which starts or ends higher than the current + number of results, then the server returns the results that are in + the set. This yields a PARTIAL return data item that has, as + payload, the original range and a potentially missing set of results + that may be shorter than the extent of the range. + + Clients need not request PARTIAL results in any particular order. + Because mailboxes may change, clients will often wish to use PARTIAL + in combination with UPDATE, especially if the intent is to walk a + large set of results; however, these return options do not interact + -- the UPDATE will provide notifications for all matching results. + + // Recall from A01 that there are 23764 results. + C: A02 UID SEARCH RETURN (PARTIAL 23500:24000) UNDELETED + UNKEYWORD $Junk + C: A03 UID SEARCH RETURN (PARTIAL 1:500) UNDELETED + UNKEYWORD $Junk + C: A04 UID SEARCH RETURN (PARTIAL 24000:24500) UNDELETED + UNKEYWORD $Junk + S: * ESEARCH (TAG "A02") UID PARTIAL (23500:24000 ...) + // 264 results in set syntax elided, + // this spans the end of the results. + S: A02 OK Completed. + S: * ESEARCH (TAG "A03") UID PARTIAL (1:500 ...) + // 500 results in set syntax elided. + S: A03 OK Completed. + S: * ESEARCH (TAG "A04") UID PARTIAL (24000:24500 NIL) + // No results are present, this is beyond the end of the results. + S: A04 OK Completed. + +4.5. Caching Results + + Server implementations MAY cache results from a SEARCH or SORT, + whether or not hinted to by CONTEXT, in order to make subsequent + searches more efficient, perhaps by recommencing a subsequent PARTIAL + search where a previous search left off. However, servers MUST + behave identically whether or not internal caching is taking place; + therefore, any such cache is required to be updated as changes to the + mailbox occur. An alternate strategy would be to discard results + when any change occurs to the mailbox. + + + + + + + + + + +Cridland & King Standards Track [Page 11] + +RFC 5267 IMAP CONTEXT July 2008 + + +5. Formal Syntax + + The collected formal syntax. This uses ABNF as defined in [ABNF]. + It includes definitions from [IMAP], [IMAP-ABNF], and [SORT]. + + capability =/ "CONTEXT=SEARCH" / "CONTEXT=SORT" / "ESORT" + ;; <capability> from [IMAP] + + command-select =/ "CANCELUPDATE" 1*(SP quoted) + ;; <command-select> from [IMAP] + + context-position = number + ;; Context position may be 0 for SEARCH result additions. + ;; <number> from [IMAP] + + modifier-context = "CONTEXT" + + modifier-partial = "PARTIAL" SP partial-range + + partial-range = nz-number ":" nz-number + ;; A range 500:400 is the same as 400:500. + ;; This is similar to <seq-range> from [IMAP], + ;; but cannot contain "*". + + modifier-update = "UPDATE" + + search-return-opt =/ modifier-context / modifier-partial / + modifier-update + ;; All conform to <search-return-opt>, from [IMAP-ABNF] + + resp-text-code =/ "NOUPDATE" SP quoted + ;; <resp-text-code> from [IMAP] + + ret-data-addto = "ADDTO" + SP "(" context-position SP sequence-set + *(SP context-position SP sequence-set) + ")" + ;; <sequence-set> from [IMAP] + + ret-data-partial = "PARTIAL" + SP "(" partial-range SP partial-results ")" + ;; <partial-range> is the requested range. + + partial-results = sequence-set / "NIL" + ;; <sequence-set> from [IMAP] + ;; NIL indicates no results correspond to the requested range. + + + + + +Cridland & King Standards Track [Page 12] + +RFC 5267 IMAP CONTEXT July 2008 + + + ret-data-removefrom = "REMOVEFROM" + SP "(" context-position SP sequence-set + *(SP context-position SP sequence-set) + ")" + ;; <sequence-set> from [IMAP] + + search-return-data =/ ret-data-partial / ret-data-addto / + ret-data-removefrom + ;; All conform to <search-return-data>, from [IMAP-ABNF] + + sort =/ extended-sort + ;; <sort> from [SORT] + + extended-sort = ["UID" SP] "SORT" search-return-opts + SP sort-criteria SP search-criteria + ;; <search-return-opts> from [IMAP-ABNF] + ;; <sort-criteria> and <search-criteria> from [SORT] + +6. Security Considerations + + This document defines additional IMAP4 capabilities. As such, it + does not change the underlying security considerations of [IMAP]. + The authors and reviewers believe that no new security issues are + introduced with these additional IMAP4 capabilities. + + Creation of a large number of contexts may provide an avenue for + denial-of-service attacks by authorized users. Implementors may + reduce this by limiting the number of contexts possible to create, + via the protocol features described in Section 4.3.1; by reducing the + impact of contexts by the implementation strategies described in + Appendix B; and by logging context creation and usage so that + administrative remedies may be applied. + +7. IANA Considerations + + IMAP4 capabilities are registered by publishing a Standards Track or + IESG-approved Experimental RFC. + + This document defines the ESORT, CONTEXT=SEARCH, and CONTEXT=SORT + IMAP capabilities. IANA has added them to the registry accordingly. + +8. Acknowledgements + + Much of the design of this extension can be found in ACAP. Valuable + comments, both in agreement and in dissent, were received from Alexey + Melnikov, Arnt Gulbrandsen, Cyrus Daboo, Filip Navara, Mark Crispin, + Peter Coates, Philip Van Hoof, Randall Gellens, Timo Sirainen, Zoltan + + + + +Cridland & King Standards Track [Page 13] + +RFC 5267 IMAP CONTEXT July 2008 + + + Ordogh, and others, and many of these comments have had significant + influence on the design or the text. The authors are grateful to all + those involved, including those not mentioned here. + +9. References + +9.1. Normative References + + [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", STD 68, RFC 5234, January 2008. + + [ESEARCH] Melnikov, A. and D. Cridland, "IMAP4 Extension to SEARCH + Command for Controlling What Kind of Information Is + Returned", RFC 4731, November 2006. + + [IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [IMAP-ABNF] Melnikov, A. and C. Daboo, "Collected Extensions to + IMAP4 ABNF", RFC 4466, April 2006. + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [SORT] Crispin, M. and K. Murchison, "Internet Message Access + Protocol - SORT and THREAD Extensions", RFC 5256, + June 2008. + +9.2. Informative References + + [ACAP] Newman, C. and J. Myers, "ACAP -- Application + Configuration Access Protocol", RFC 2244, November 1997. + + [IDLE] Leiba, B., "IMAP4 IDLE command", RFC 2177, June 1997. + + [NOTIFY] Melnikov, A., Gulbrandsen, A., and C. King, "The IMAP + NOTIFY Extension", Work in Progress, March 2008. + + + + + + + + + + + + + + +Cridland & King Standards Track [Page 14] + +RFC 5267 IMAP CONTEXT July 2008 + + +Appendix A. Cookbook + +A.1. Virtual Mailboxes + + It is possible to use the facilities described within this memo to + create a facility largely similar to a virtual mailbox, but handled + on the client side. + + Initially, the client SELECTs the real "backing" mailbox. Next, it + can switch to a filtered view at any time by issuing a RETURN (COUNT + UPDATE CONTEXT), and using RETURN (PARTIAL x:y) as the user scrolls, + feeding the results into a FETCH as required to populate summary + views. + + A typically useful view is "UID SORT (DATE) RETURN (...) UTF-8 + UNSEEN UNDELETED", which can be used to show the mailbox sorted into + INTERNALDATE order, filtered to only show messages which are unread + and not yet deleted. + +A.2. Trash Mailboxes + + Certain contexts are particularly useful for client developers + wishing to present something similar to the common trash mailbox + metaphor in limited bandwidth. The simple criteria of UNDELETED only + matches undeleted messages, and the corresponding DELETED search key + can be used to display a per-mailbox trash-like virtual mailbox. + +A.3. Immediate EXPUNGE Notifications + + The command "SEARCH RETURN (UPDATE) ALL" can be used to create a + context that notifies immediately about expunged messages, yet will + not affect message sequence numbers until the normal EXPUNGE message + can be sent. This may be useful for clients wishing to show this + behavior without losing the benefit of sequence numbering. + +A.4. Monitoring Counts + + A client need not maintain any result cache at all, but instead it + can maintain a simple count of messages matching the search criteria. + Typically, this would use the SEARCH command, as opposed to UID + SEARCH, due to its smaller representation. Such usage might prove + useful in monitoring the number of flagged, but unanswered, messages, + for example, with "SEARCH RETURN (UPDATE COUNT) FLAGGED UNANSWERED". + + + + + + + + +Cridland & King Standards Track [Page 15] + +RFC 5267 IMAP CONTEXT July 2008 + + +A.5. Resynchronizing Contexts + + The creation of a context, and immediate access to it, can all be + accomplished in a single round-trip. Therefore, whilst it is + possible to elide resynchronization if no changes have occurred, it + is simpler in most cases to resynchronize by simply recreating the + context. + +Appendix B. Server Implementation Notes + + Although a server may cache the results, this is neither mandated nor + required, especially when the client uses SEARCH or UID SEARCH + commands. UPDATE processing, for example, can be achieved + efficiently by comparison of the old flag state (if any) and the new, + and PARTIAL can be achieved by re-running the search until the + suitable window is required. This is a result of there being no + snapshot facility. + + For example, on a new message, the server can simply test for matches + against all current UPDATE context search programs, and for any that + match, send the ADDTO return data. + + Similarly, for a flag change on an existing message, the server can + check whether the message matched with its old flags, whether it + matches with new flags, and provide ADDTO or REMOVEFROM return data + accordingly if these results differ. + + For PARTIAL requests, the server can perform a full search, + discarding results until the lower bound is hit, and stopping the + search when sufficient results have been obtained. + + With some additional state, it is possible to restart PARTIAL + searches, thus avoiding performing the initial discard phase. + + For the best performance, however, caching the full search results is + needed, which can allow for faster responses at the expense of + memory. One reasonable strategy would be to balance this trade-off + at run-time, discarding search results after a suitable timeout, and + regenerating them as required. + + This yields state requirements of storing the search program for any + UPDATE contexts, and optionally storing both search program and + (updated) results for further contexts as required. + + + + + + + + +Cridland & King Standards Track [Page 16] + +RFC 5267 IMAP CONTEXT July 2008 + + + Note that in the absence of a server-side results cache, it may be + impossible to know if an expunged message previously matched unless + the original message is still available. Therefore, some + implementations may be forced into using a results cache in many + circumstances. + + UPDATE contexts created with SORT or UID SORT will almost certainly + require some form of results caching, however. + +Authors' Addresses + + Dave Cridland + Isode Limited + 5 Castle Business Village + 36, Station Road + Hampton, Middlesex TW12 2BX + GB + + EMail: dave.cridland@isode.com + + + Curtis King + Isode Limited + 5 Castle Business Village + 36, Station Road + Hampton, Middlesex TW12 2BX + GB + + EMail: cking@mumbo.ca + + + + + + + + + + + + + + + + + + + + + + +Cridland & King Standards Track [Page 17] + +RFC 5267 IMAP CONTEXT July 2008 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2008). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Cridland & King Standards Track [Page 18] + diff --git a/imap/docs/rfc/rfc5464.txt b/imap/docs/rfc/rfc5464.txt new file mode 100644 index 00000000..645bfd9a --- /dev/null +++ b/imap/docs/rfc/rfc5464.txt @@ -0,0 +1,1177 @@ + + + +Network Working Group C. Daboo +Request for Comments: 5464 Apple, Inc. +Category: Standards Track February 2009 + + + The IMAP METADATA Extension + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + The METADATA extension to the Internet Message Access Protocol + permits clients and servers to maintain "annotations" or "metadata" + on IMAP servers. It is possible to have annotations on a per-mailbox + basis or on the server as a whole. For example, this would allow + comments about the purpose of a particular mailbox to be "attached" + to that mailbox, or a "message of the day" containing server status + information to be made available to anyone logging in to the server. + + + + + + + + + + + + + + + + + + + + + + + + + + + +Daboo Standards Track [Page 1] + +RFC 5464 The IMAP METADATA Extension February 2009 + + +Table of Contents + + 1. Introduction and Overview . . . . . . . . . . . . . . . . . . 3 + 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 + 3. Data Model . . . . . . . . . . . . . . . . . . . . . . . . . . 4 + 3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 4 + 3.2. Namespace of Entries . . . . . . . . . . . . . . . . . . . 4 + 3.2.1. Entry Names . . . . . . . . . . . . . . . . . . . . . 5 + 3.3. Private versus Shared and Access Control . . . . . . . . . 6 + 4. IMAP Protocol Changes . . . . . . . . . . . . . . . . . . . . 7 + 4.1. General Considerations . . . . . . . . . . . . . . . . . . 7 + 4.2. GETMETADATA Command . . . . . . . . . . . . . . . . . . . 8 + 4.2.1. MAXSIZE GETMETADATA Command Option . . . . . . . . . . 9 + 4.2.2. DEPTH GETMETADATA Command Option . . . . . . . . . . . 10 + 4.3. SETMETADATA Command . . . . . . . . . . . . . . . . . . . 10 + 4.4. METADATA Response . . . . . . . . . . . . . . . . . . . . 12 + 4.4.1. METADATA Response with Values . . . . . . . . . . . . 13 + 4.4.2. Unsolicited METADATA Response without Values . . . . . 13 + 5. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 14 + 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 + 6.1. Entry and Attribute Registration Template . . . . . . . . 16 + 6.2. Server Entry Registrations . . . . . . . . . . . . . . . . 16 + 6.2.1. /shared/comment . . . . . . . . . . . . . . . . . . . 17 + 6.2.2. /shared/admin . . . . . . . . . . . . . . . . . . . . 17 + 6.3. Mailbox Entry Registrations . . . . . . . . . . . . . . . 17 + 6.3.1. /shared/comment . . . . . . . . . . . . . . . . . . . 18 + 6.3.2. /private/comment . . . . . . . . . . . . . . . . . . . 18 + 7. Security Considerations . . . . . . . . . . . . . . . . . . . 18 + 8. Normative References . . . . . . . . . . . . . . . . . . . . . 19 + Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 19 + + + + + + + + + + + + + + + + + + + + + +Daboo Standards Track [Page 2] + +RFC 5464 The IMAP METADATA Extension February 2009 + + +1. Introduction and Overview + + The goal of the METADATA extension is to provide a means for clients + to set and retrieve "annotations" or "metadata" on an IMAP server. + The annotations can be associated with specific mailboxes or the + server as a whole. The server can choose to support only server + annotations or both server and mailbox annotations. + + A server that supports both server and mailbox annotations indicates + the presence of this extension by returning "METADATA" as one of the + supported capabilities in the CAPABILITY command response. + + A server that supports only server annotations indicates the presence + of this extension by returning "METADATA-SERVER" as one of the + supported capabilities in the CAPABILITY command response. + + A server that supports unsolicited annotation change responses MUST + support the "ENABLE" [RFC5161] extension to allow clients to turn + that feature on. + + The METADATA extension adds two new commands and one new untagged + response to the IMAP base protocol. + + This extension makes the following changes to the IMAP protocol: + + o adds a new SETMETADATA command + + o adds a new GETMETADATA command + + o adds a new METADATA untagged response + + o adds a new METADATA response code + + The rest of this document describes the data model and protocol + changes more rigorously. + +2. Conventions Used in This Document + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + + Whitespace and line breaks have been added to the examples in this + document to promote readability. + + + + +Daboo Standards Track [Page 3] + +RFC 5464 The IMAP METADATA Extension February 2009 + + +3. Data Model + +3.1. Overview + + Mailboxes or the server as a whole may have zero or more annotations + associated with them. An annotation contains a uniquely named entry, + which has a value. Annotations can be added to mailboxes when a + mailbox name is provided as the first argument to the SETMETADATA + command, or to the server as a whole when the empty string is + provided as the first argument to the command. + + For example, a general comment being added to a mailbox may have an + entry name of "/comment" and a value of "Really useful mailbox". + + The protocol changes to IMAP described below allow a client to access + or change the values of any annotation entry, assuming it has + sufficient access rights to do so. + +3.2. Namespace of Entries + + Each annotation is an entry that has a hierarchical name, with each + component of the name separated by a slash ("/"). An entry name MUST + NOT contain two consecutive "/" characters and MUST NOT end with a + "/" character. + + The value of an entry is NIL (has no value), or a string or binary + data of zero or more octets. A string MAY contain multiple lines of + text. Clients MUST use the CRLF (0x0D 0x0A) character octet sequence + to represent line ends in a multi-line string value. + + Entry names MUST NOT contain asterisk ("*") or percent ("%") + characters and MUST NOT contain non-ASCII characters or characters + with octet values in the range 0x00 to 0x19. Invalid entry names + result in a BAD response in any IMAP command in which they are used. + + Entry names are case-insensitive. + + Use of control or punctuation characters in entry names is strongly + discouraged. + + This specification defines an initial set of entry names available + for use with mailbox and server annotations. In addition, an + extension mechanism is described to allow additional names to be + added for extensibility. + + The first component in entry names defines the scope of the + annotation. Currently, only the prefixes "/private" or "/shared" are + defined. These prefixes are used to indicate whether an annotation + + + +Daboo Standards Track [Page 4] + +RFC 5464 The IMAP METADATA Extension February 2009 + + + is stored on a per-user basis ("/private") and not visible to other + users, or whether an annotation is shared between authorized users + ("/shared") with a single value that can be read and changed by + authorized users with appropriate access. See Section 3.3 for + details. + + Entry names can have any number of components starting at 2, unless + they fall under the vendor namespaces (i.e., have a /shared/vendor/ + <vendor-token> or /private/vendor/<vendor-token> prefix as described + below), in which case they have at least 4 components. + +3.2.1. Entry Names + + Entry names MUST be specified in a Standards Track or IESG-approved + Experimental RFC, or fall under the vendor namespace. See + Section 6.1 for the registration template. + +3.2.1.1. Server Entries + + These entries are set or retrieved when the mailbox name argument to + the new SETMETADATA or GETMETADATA command is the empty string. + + /shared/comment + + Defines a comment or note that is associated with the server and + that is shared with authorized users of the server. + + /shared/admin + + Indicates a method for contacting the server administrator. The + value MUST be a URI (e.g., a mailto: or tel: URL). This entry is + always read-only -- clients cannot change it. It is visible to + authorized users of the system. + + /shared/vendor/<vendor-token> + + Defines the top level of shared entries associated with the + server, as created by a particular product of some vendor. This + entry can be used by vendors to provide server- or client-specific + annotations. The vendor-token MUST be registered with IANA, using + the Application Configuration Access Protocol (ACAP) [RFC2244] + vendor subtree registry. + + /private/vendor/<vendor-token> + + Defines the top level of private entries associated with the + server, as created by a particular product of some vendor. This + entry can be used by vendors to provide server- or client-specific + + + +Daboo Standards Track [Page 5] + +RFC 5464 The IMAP METADATA Extension February 2009 + + + annotations. The vendor-token MUST be registered with IANA, using + the ACAP [RFC2244] vendor subtree registry. + +3.2.1.2. Mailbox Entries + + These entries are set or retrieved when the mailbox name argument to + the new SETMETADATA or GETMETADATA command is not the empty string. + + /shared/comment + + Defines a shared comment or note associated with a mailbox. + + /private/comment + + Defines a private (per-user) comment or note associated with a + mailbox. + + /shared/vendor/<vendor-token> + + Defines the top level of shared entries associated with a specific + mailbox, as created by a particular product of some vendor. This + entry can be used by vendors to provide client-specific + annotations. The vendor-token MUST be registered with IANA, using + the ACAP [RFC2244] vendor subtree registry. + + /private/vendor/<vendor-token> + + Defines the top level of private entries associated with a + specific mailbox, as created by a particular product of some + vendor. This entry can be used by vendors to provide client- + specific annotations. The vendor-token MUST be registered with + IANA, using the ACAP [RFC2244] vendor subtree registry. + +3.3. Private versus Shared and Access Control + + In the absence of the ACL (Access Control List) extension [RFC4314], + users can only set and retrieve private or shared mailbox annotations + on a mailbox that exists and is returned to them via a LIST or LSUB + command, and on which they have either read or write access to the + actual message content of the mailbox (as determined by the READ-ONLY + and READ-WRITE response codes as described in Section 5.2 of + [RFC4314]). + + When the ACL extension [RFC4314] is present, users can only set and + retrieve private or shared mailbox annotations on a mailbox on which + they have the "l" right and any one of the "r", "s", "w", "i", or "p" + rights. + + + + +Daboo Standards Track [Page 6] + +RFC 5464 The IMAP METADATA Extension February 2009 + + + If a client attempts to set or retrieve annotations on mailboxes that + do not satisfy the conditions above, the server MUST respond with a + NO response. + + Users can always retrieve private or shared server annotations if + they exist. Servers MAY restrict the creation of private or shared + server annotations as appropriate. When restricted, the server MUST + return a NO response when the SETMETADATA command is used to try to + create a server annotation. + + If the METADATA extension is present, support for shared annotations + is REQUIRED, whilst support for private annotations is OPTIONAL. + This recognizes the fact that support for private annotations may + introduce significantly more complexity to a server in terms of + tracking ownership of the annotations, how quota is determined for + users based on their own annotations, etc. + +4. IMAP Protocol Changes + +4.1. General Considerations + + The new SETMETADATA command and the METADATA response each have a + mailbox name argument. An empty string is used for the mailbox name + to signify server annotations. A non-empty string is used to signify + mailbox annotations attached to the corresponding mailbox. + + Servers SHOULD ensure that mailbox annotations are automatically + moved when the mailbox they refer to is renamed, i.e., the + annotations follow the mailbox. This applies to a rename of the + INBOX, with the additional behavior that the annotations are copied + from the original INBOX to the renamed mailbox, i.e., mailbox + annotations are preserved on the INBOX when it is renamed. + + Servers SHOULD delete annotations for a mailbox when the mailbox is + deleted, so that a mailbox created with the same name as a previously + existing mailbox does not inherit the old mailbox annotations. + + Servers SHOULD allow annotations on all 'types' of mailboxes, + including ones reporting \Noselect for their LIST response. Servers + can implicitly remove \Noselect mailboxes when all child mailboxes + are removed, and, at that time any annotations associated with the + \Noselect mailbox SHOULD be removed. + + The server is allowed to impose limitations on the size of any one + annotation or the total number of annotations for a single mailbox or + for the server as a whole. However, the server MUST accept an + annotation data size of at least 1024 bytes, and an annotation count + per server or mailbox of at least 10. + + + +Daboo Standards Track [Page 7] + +RFC 5464 The IMAP METADATA Extension February 2009 + + + Some annotations may be "read-only" -- i.e., they are set by the + server and cannot be changed by the client. Also, such annotations + may be "computed" -- i.e., the value changes based on underlying + properties of the mailbox or server. For example, an annotation + reporting the total size of all messages in the mailbox would change + as messages are added or removed. Or, an annotation containing an + IMAP URL for the mailbox would change if the mailbox was renamed. + + Servers MAY support sending unsolicited responses for use when + annotations are changed by some "third-party" (see Section 4.4). In + order to do so, servers MUST support the ENABLE command [RFC5161] and + MUST only send unsolicited responses if the client used the ENABLE + command [RFC5161] extension with the capability string "METADATA" or + "METADATA-SERVER" earlier in the session, depending on which of those + capabilities is supported by the server. + +4.2. GETMETADATA Command + + This extension adds the GETMETADATA command. This allows clients to + retrieve server or mailbox annotations. + + This command is only available in authenticated or selected state + [RFC3501]. + + Arguments: mailbox-name + options + entry-specifier + + Responses: required METADATA response + + Result: OK - command completed + NO - command failure: can't access annotations on + the server + BAD - command unknown or arguments invalid + + When the mailbox name is the empty string, this command retrieves + server annotations. When the mailbox name is not empty, this command + retrieves annotations on the specified mailbox. + + Options MAY be included with this command and are defined below. + + Example: + + C: a GETMETADATA "" /shared/comment + S: * METADATA "" (/shared/comment "Shared comment") + S: a OK GETMETADATA complete + + + + + +Daboo Standards Track [Page 8] + +RFC 5464 The IMAP METADATA Extension February 2009 + + + In the above example, the contents of the value of the "/shared/ + comment" server entry is requested by the client and returned by + the server. + + Example: + + C: a GETMETADATA "INBOX" /private/comment + S: * METADATA "INBOX" (/private/comment "My own comment") + S: a OK GETMETADATA complete + + In the above example, the contents of the value of the "/private/ + comment" mailbox entry for the mailbox "INBOX" is requested by the + client and returned by the server. + + Entry specifiers can be lists of atomic specifiers, so that multiple + annotations may be returned in a single GETMETADATA command. + + Example: + + C: a GETMETADATA "INBOX" (/shared/comment /private/comment) + S: * METADATA "INBOX" (/shared/comment "Shared comment" + /private/comment "My own comment") + S: a OK GETMETADATA complete + + In the above example, the values of the two server entries + "/shared/comment" and "/private/comment" on the mailbox "INBOX" + are requested by the client and returned by the server. + +4.2.1. MAXSIZE GETMETADATA Command Option + + When the MAXSIZE option is specified with the GETMETADATA command, it + restricts which entry values are returned by the server. Only entry + values that are less than or equal in octet size to the specified + MAXSIZE limit are returned. If there are any entries with values + larger than the MAXSIZE limit, the server MUST include the METADATA + LONGENTRIES response code in the tagged OK response for the + GETMETADATA command. The METADATA LONGENTRIES response code returns + the size of the biggest entry value requested by the client that + exceeded the MAXSIZE limit. + + Example: + + C: a GETMETADATA "INBOX" (MAXSIZE 1024) + (/shared/comment /private/comment) + S: * METADATA "INBOX" (/private/comment "My own comment") + S: a OK [METADATA LONGENTRIES 2199] GETMETADATA complete + + + + + +Daboo Standards Track [Page 9] + +RFC 5464 The IMAP METADATA Extension February 2009 + + + In the above example, the values of the two server entries + "/shared/comment" and "/private/comment" on the mailbox "INBOX" + are requested by the client, which wants to restrict the size of + returned values to 1024 octets. In this case, the "/shared/ + comment" entry value is 2199 octets and is not returned. + +4.2.2. DEPTH GETMETADATA Command Option + + When the DEPTH option is specified with the GETMETADATA command, it + extends the list of entry values returned by the server. For each + entry name specified in the GETMETADATA command, the server returns + the value of the specified entry name (if it exists), plus all + entries below the entry name up to the specified DEPTH. Three values + are allowed for DEPTH: + + "0" - no entries below the specified entry are returned + "1" - only entries immediately below the specified entry are returned + "infinity" - all entries below the specified entry are returned + + Thus, "depth 1" for an entry "/a" will match "/a" as well as its + children entries (e.g., "/a/b"), but will not match grandchildren + entries (e.g., "/a/b/c"). + + If the DEPTH option is not specified, this is the same as specifying + "DEPTH 0". + + Example: + + C: a GETMETADATA "INBOX" (DEPTH 1) + (/private/filters/values) + S: * METADATA "INBOX" (/private/filters/values/small + "SMALLER 5000" /private/filters/values/boss + "FROM \"boss@example.com\"") + S: a OK GETMETADATA complete + + In the above example, 2 entries below the /private/filters/values + entry exist on the mailbox "INBOX": "/private/filters/values/ + small" and "/private/filters/values/boss". + +4.3. SETMETADATA Command + + This extension adds the SETMETADATA command. This allows clients to + set annotations. + + This command is only available in authenticated or selected state + [RFC3501]. + + + + + +Daboo Standards Track [Page 10] + +RFC 5464 The IMAP METADATA Extension February 2009 + + + Arguments: mailbox-name + entry + value + list of entry, values + + Responses: no specific responses for this command + + Result: OK - command completed + NO - command failure: can't set annotations, + or annotation too big or too many + BAD - command unknown or arguments invalid + + This command sets the specified list of entries by adding or + replacing the specified values provided, on the specified existing + mailboxes or on the server (if the mailbox argument is the empty + string). Clients can use NIL for the value of entries it wants to + remove. The server SHOULD NOT return a METADATA response containing + the updated annotation data. Clients MUST NOT assume that a METADATA + response will be sent, and MUST assume that if the command succeeds, + then the annotation has been changed. + + If the server is unable to set an annotation because the size of its + value is too large, the server MUST return a tagged NO response with + a "[METADATA MAXSIZE NNN]" response code when NNN is the maximum + octet count that it is willing to accept. + + If the server is unable to set a new annotation because the maximum + number of allowed annotations has already been reached, the server + MUST return a tagged NO response with a "[METADATA TOOMANY]" response + code. + + If the server is unable to set a new annotation because it does not + support private annotations on one of the specified mailboxes, the + server MUST return a tagged NO response with a "[METADATA NOPRIVATE]" + response code. + + When any one annotation fails to be set, resulting in a tagged NO + response from the server, then the server MUST NOT change the values + for other annotations specified in the SETMETADATA command. + + Example: + + C: a SETMETADATA INBOX (/private/comment {33} + S: + ready for data + My new comment across + two lines. + ) + S: a OK SETMETADATA complete + + + +Daboo Standards Track [Page 11] + +RFC 5464 The IMAP METADATA Extension February 2009 + + + In the above example, the entry "/private/comment" for the mailbox + "INBOX" is created (if not already present) and the value set to a + multi-line string. + + Example: + + C: a SETMETADATA INBOX (/private/comment NIL) + S: a OK SETMETADATA complete + + In the above example, the entry "/private/comment" is removed from + the mailbox "INBOX". + + Multiple entries can be set in a single SETMETADATA command by + listing entry-value pairs in the list. + + Example: + + C: a SETMETADATA INBOX (/private/comment "My new comment" + /shared/comment "This one is for you!") + S: a OK SETMETADATA complete + + In the above example, the entries "/private/comment" and "/shared/ + comment" for the mailbox "INBOX" are created (if not already + present) and the values set as specified. + + Example: + + C: a SETMETADATA INBOX (/private/comment "My new comment") + S: a NO [METADATA TOOMANY] SETMETADATA failed + + In the above example, the server is unable to set the requested + (new) annotation as it has reached the limit on the number of + annotations it can support on the specified mailbox. + +4.4. METADATA Response + + The METADATA response displays results of a GETMETADATA command, or + can be returned as an unsolicited response at any time by the server + in response to a change in a server or mailbox annotation. + + When unsolicited responses are activated by the ENABLE [RFC5161] + command for this extension, servers MUST send unsolicited METADATA + responses if server or mailbox annotations are changed by a third- + party, allowing servers to keep clients updated with changes. + + Unsolicited METADATA responses MUST only contain entry names, not the + values. If the client wants to update any cached values, it must + explicitly retrieve those using a GETMETADATA command. + + + +Daboo Standards Track [Page 12] + +RFC 5464 The IMAP METADATA Extension February 2009 + + + The METADATA response can contain multiple entries in a single + response, but the server is free to return multiple responses for + each entry or group of entries, if it desires. + + This response is only available in authenticated or selected state + [RFC3501]. + +4.4.1. METADATA Response with Values + + The response consists of a list of entry-value pairs. + + Example: + + C: a GETMETADATA "" /shared/comment + S: * METADATA "" (/shared/comment "My comment") + S: a OK GETMETADATA complete + + In the above example, a single entry with its value is returned by + the server. + + Example: + + C: a GETMETADATA "INBOX" /private/comment /shared/comment + S: * METADATA "INBOX" (/private/comment "My comment" + /shared/comment "Its sunny outside!") + S: a OK GETMETADATA complete + + In the above example, two entries and their values are returned by + the server. + + Example: + + C: a GETMETADATA "INBOX" /private/comment /shared/comment + S: * METADATA "INBOX" (/private/comment "My comment") + S: * METADATA "INBOX" (/shared/comment "Its sunny outside!") + S: a OK GETMETADATA complete + + In the above example, the server returns two separate responses + for each of the two entries requested. + +4.4.2. Unsolicited METADATA Response without Values + + The response consists of a list of entries, each of which have + changed on the server or mailbox. + + Example: + + + + + +Daboo Standards Track [Page 13] + +RFC 5464 The IMAP METADATA Extension February 2009 + + + C: a NOOP + S: * METADATA "" /shared/comment + S: a OK NOOP complete + + In the above example, the server indicates that the "/shared/ + comment" server entry has been changed. + + Example: + + C: a NOOP + S: * METADATA "INBOX" /shared/comment /private/comment + S: a OK NOOP complete + + In the above example, the server indicates a change to two mailbox + entries. + +5. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [RFC5234]. + + Non-terminals referenced but not defined below are as defined by + [RFC3501], with the new definitions in [RFC4466] superseding those in + [RFC3501]. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper or lower case characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + capability =/ "METADATA" / "METADATA-SERVER" + ; defines the capabilities for this extension. + + command-auth =/ setmetadata / getmetadata + ; adds to original IMAP command + + entries = entry / + "(" entry *(SP entry) ")" + ; entry specifiers + + entry = astring + ; slash-separated path to entry + ; MUST NOT contain "*" or "%" + + entry-value = entry SP value + + entry-values = "(" entry-value *(SP entry-value) ")" + + + + +Daboo Standards Track [Page 14] + +RFC 5464 The IMAP METADATA Extension February 2009 + + + entry-list = entry *(SP entry) + ; list of entries used in unsolicited + ; METADATA response + + getmetadata = "GETMETADATA" [SP getmetadata-options] + SP mailbox SP entries + ; empty string for mailbox implies + ; server annotation. + + getmetadata-options = "(" getmetadata-option + *(SP getmetadata-option) ")" + + getmetadata-option = tagged-ext-label [SP tagged-ext-val] + ; tagged-ext-label and tagged-ext-val + ; are defined in [RFC4466]. + + maxsize-opt = "MAXSIZE" SP number + ; Used as a getmetadata-option + + metadata-resp = "METADATA" SP mailbox SP + (entry-values / entry-list) + ; empty string for mailbox implies + ; server annotation. + + response-payload =/ metadata-resp + ; adds to original IMAP data responses + + resp-text-code =/ "METADATA" SP "LONGENTRIES" SP number + ; new response codes for GETMETADATA + + resp-text-code =/ "METADATA" SP ("MAXSIZE" SP number / + "TOOMANY" / "NOPRIVATE") + ; new response codes for SETMETADATA + ; failures + + scope-opt = "DEPTH" SP ("0" / "1" / "infinity") + ; Used as a getmetadata-option + + setmetadata = "SETMETADATA" SP mailbox + SP entry-values + ; empty string for mailbox implies + ; server annotation. + + value = nstring / literal8 + + + + + + + +Daboo Standards Track [Page 15] + +RFC 5464 The IMAP METADATA Extension February 2009 + + +6. IANA Considerations + + All entries MUST have either "/shared" or "/private" as a prefix. + Entry names MUST be specified in a Standards Track or IESG-approved + Experimental RFC, or fall under the vendor namespace (i.e., use + /shared/vendor/<vendor-token> or /private/vendor/<vendor-token> as + the prefix). + + Each entry registration MUST include a content-type that is used to + indicate the nature of the annotation value. Where applicable, a + charset parameter MUST be included with the content-type. + +6.1. Entry and Attribute Registration Template + + To: iana@iana.org + Subject: IMAP METADATA Entry Registration + + Type: [Either "Mailbox" or "Server"] + + Name: [the name of the entry] + + Description: [a description of what the entry is for] + + Content-type: [MIME Content-Type and charset for the entry value] + + RFC Number: [for entries published as RFCs] + + Contact: [email and/or physical address to contact for + additional information] + +6.2. Server Entry Registrations + + The following templates specify the IANA registrations of annotation + entries specified in this document. + + + + + + + + + + + + + + + + + +Daboo Standards Track [Page 16] + +RFC 5464 The IMAP METADATA Extension February 2009 + + +6.2.1. /shared/comment + + To: iana@iana.org + Subject: IMAP METADATA Entry Registration + + Type: Server + + Name: /shared/comment + + Description: Defines a comment or note that is associated + with the server and that is shared with + authorized users of the server. + + Content-type: text/plain; charset=utf-8 + + RFC Number: RFC 5464 + + Contact: IMAP Extensions mailto:ietf-imapext@imc.org + +6.2.2. /shared/admin + + To: iana@iana.org + Subject: IMAP METADATA Entry Registration + + Type: Server + + Name: /shared/admin + + Description: Indicates a method for contacting the server + administrator. The value MUST be a URI (e.g., a + mailto: or tel: URL). This entry is always + read-only -- clients cannot change it. It is visible + to authorized users of the system. + + Content-type: text/plain; charset=utf-8 + + RFC Number: RFC 5464 + + Contact: IMAP Extensions mailto:ietf-imapext@imc.org + +6.3. Mailbox Entry Registrations + + The following templates specify the IANA registrations of annotation + entries specified in this document. + + + + + + + +Daboo Standards Track [Page 17] + +RFC 5464 The IMAP METADATA Extension February 2009 + + +6.3.1. /shared/comment + + To: iana@iana.org + Subject: IMAP METADATA Entry Registration + + Type: Mailbox + + Name: /shared/comment + + Description: Defines a shared comment or note associated with a + mailbox. + + Content-type: text/plain; charset=utf-8 + + RFC Number: RFC 5464 + + Contact: IMAP Extensions mailto:ietf-imapext@imc.org + +6.3.2. /private/comment + + To: iana@iana.org + Subject: IMAP METADATA Entry Registration + + Type: Mailbox + + Name: /private/comment + + Description: Defines a private comment or note associated with a + mailbox. + + Content-type: text/plain; charset=utf-8 + + RFC Number: RFC 5464 + + Contact: IMAP Extensions mailto:ietf-imapext@imc.org + +7. Security Considerations + + The security considerations in Section 11 of [RFC3501] apply here + with respect to protecting annotations from snooping. Servers MAY + choose to only support the METADATA and/or METADATA-SERVER extensions + after a privacy layer has been negotiated by the client. + + Annotations can contain arbitrary data of varying size. As such, + servers MUST ensure that size limits are enforced to prevent a user + from using up all available space on a server and preventing use by + others. Clients MUST treat annotation data values as an "untrusted" + source of data as it is possible for it to contain malicious content. + + + +Daboo Standards Track [Page 18] + +RFC 5464 The IMAP METADATA Extension February 2009 + + + Annotations whose values are intended to remain private MUST be + stored only in entries that have the "/private" prefix on the entry + name. + + Excluding the above issues, the METADATA extension does not raise any + security considerations that are not present in the base IMAP + protocol, and these issues are discussed in [RFC3501]. + +8. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2244] Newman, C. and J. Myers, "ACAP -- Application + Configuration Access Protocol", RFC 2244, November 1997. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL) Extension", + RFC 4314, December 2005. + + [RFC4466] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4 + ABNF", RFC 4466, April 2006. + + [RFC5161] Gulbrandsen, A. and A. Melnikov, "The IMAP ENABLE + Extension", RFC 5161, March 2008. + + [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", STD 68, RFC 5234, January 2008. + +Appendix A. Acknowledgments + + The ideas expressed in this document are based on the message + annotation document that was co-authored by Randall Gellens. The + author would like to thank the following individuals for contributing + their ideas and support for writing this specification: Dave + Cridland, Arnt Gulbrandsen, Dan Karp, Alexey Melnikov, Ken Murchison, + Chris Newman, and Michael Wener. + + + + + + + + + + + + +Daboo Standards Track [Page 19] + +RFC 5464 The IMAP METADATA Extension February 2009 + + +Author's Address + + Cyrus Daboo + Apple Inc. + 1 Infinite Loop + Cupertino, CA 95014 + USA + + EMail: cyrus@daboo.name + URI: http://www.apple.com/ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Daboo Standards Track [Page 20] + +RFC 5464 The IMAP METADATA Extension February 2009 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2009). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND + THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS + OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF + THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + + + + + + + + + + + +Daboo Standards Track [Page 21] + + diff --git a/imap/docs/rfc/rfc5465.txt b/imap/docs/rfc/rfc5465.txt new file mode 100644 index 00000000..3fe5bcfb --- /dev/null +++ b/imap/docs/rfc/rfc5465.txt @@ -0,0 +1,1235 @@ + + + + + + +Network Working Group A. Gulbrandsen +Request for Comments: 5465 Oryx Mail Systems GmbH +Updates: 5267 C. King +Category: Standards Track A. Melnikov + Isode Ltd. + February 2009 + + + The IMAP NOTIFY Extension + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (c) 2009 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents (http://trustee.ietf.org/ + license-info) in effect on the date of publication of this document. + Please review these documents carefully, as they describe your rights + and restrictions with respect to this document. + +Abstract + + This document defines an IMAP extension that allows a client to + request specific kinds of unsolicited notifications for specified + mailboxes, such as messages being added to or deleted from such + mailboxes. + + + + + + + + + + + + + + + + +Gulbrandsen, et al. Standards Track [Page 1] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + +Table of Contents + + 1. Overview and Rationale ..........................................3 + 2. Conventions Used in This Document ...............................4 + 3. The NOTIFY Extension ............................................4 + 3.1. The NOTIFY Command .........................................4 + 4. Interaction with the IDLE Command ...............................8 + 5. Event Types .....................................................8 + 5.1. FlagChange and AnnotationChange ............................9 + 5.2. MessageNew .................................................9 + 5.3. MessageExpunge ............................................10 + 5.4. MailboxName ...............................................11 + 5.5. SubscriptionChange ........................................12 + 5.6. MailboxMetadataChange .....................................12 + 5.7. ServerMetadataChange ......................................13 + 5.8. Notification Overflow .....................................13 + 5.9. ACL (Access Control List) Changes .........................13 + 6. Mailbox Specification ..........................................14 + 6.1. Mailbox Specifiers Affecting the Currently + Selected Mailbox ..........................................14 + 6.2. Personal ..................................................15 + 6.3. Inboxes ...................................................15 + 6.4. Subscribed ................................................15 + 6.5. Subtree ...................................................15 + 6.6. Mailboxes .................................................16 + 7. Extension to SEARCH and SORT Commands ..........................16 + 8. Formal Syntax ..................................................16 + 9. Security Considerations ........................................19 + 10. IANA Considerations ...........................................19 + 10.1. Initial LIST-EXTENDED Extended Data Item Registrations ...19 + 11. Acknowledgements ..............................................20 + 12. Normative References ..........................................20 + 13. Informative References ........................................21 + + + + + + + + + + + + + + + + + + +Gulbrandsen, et al. Standards Track [Page 2] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + +1. Overview and Rationale + + The IDLE command (defined in [RFC2177]) provides a way for the client + to go into a mode where the IMAP server pushes it notifications about + IMAP mailstore events for the selected mailbox. However, the IDLE + extension doesn't restrict or control which server events can be + sent, or what information the server sends in response to each event. + Also, IDLE only applies to the selected mailbox, thus requiring an + additional TCP connection per mailbox. + + This document defines an IMAP extension that allows clients to + express their preferences about unsolicited events generated by the + server. The extension allows clients to only receive events that + they are interested in, while servers know that they don't need to go + to the effort of generating certain types of untagged responses. + + Without the NOTIFY command defined in this document, an IMAP server + will only send information about mailstore changes to the client in + the following cases: + + - as the result of a client command (e.g., FETCH responses to a + FETCH or STORE command), + - as unsolicited responses sent just before the end of a command + (e.g., EXISTS or EXPUNGE) as the result of changes in other + sessions, and + - during an IDLE command. + + The NOTIFY command extends what information may be returned in those + last two cases, and also permits and requires the server to send + information about updates between commands. The NOTIFY command also + allows for the client to extend what information is sent unsolicited + about the selected mailbox and to request some update information to + be sent regarding other mailboxes. + + The interaction between IDLE and NOTIFY commands is described in + Section 4. + + For the new messages delivered to or appended to the selected + mailbox, the NOTIFY command can be used to request that a set of + attributes be sent to the client in an unsolicited FETCH response. + This allows a client to be a passive recipient of events and new mail + and to be able to maintain full synchronisation without having to + issue any subsequent commands except to modify the state of the + mailbox on the server. + + + + + + + +Gulbrandsen, et al. Standards Track [Page 3] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + + Some mobile clients, however, may want mail "pushed" only for mail + that matches a SEARCH pattern. To meet that need, [RFC5267] is + augmented by this document to extend the UPDATE return option to + specify a list of fetch-atts to be returned when a new message is + delivered or appended in another session. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + + The acronym MSN stands for Message Sequence Numbers (see Section + 2.3.1.2 of [RFC3501]). + + Example lines prefaced by "C:" are sent by the client and ones + prefaced by "S:", by the server. "[...]" means elision. + +3. The NOTIFY Extension + + IMAP servers that support this extension advertise the NOTIFY + capability. This extension adds the NOTIFY command as defined in + Section 5.1. + + A server implementing this extension is not required to implement + LIST-EXTENDED [RFC5258], even though a NOTIFY-compliant server must + be able to return extended LIST responses, defined in [RFC5258]. + +3.1. The NOTIFY Command + + Arguments: "SET" + Optional STATUS indicator + Mailboxes to be watched + Events about which to notify the client + + Or + Arguments: "NONE" + + Responses: Possibly untagged STATUS responses (for SET) + + Result: OK - The server will notify the client as requested. + NO - Unsupported NOTIFY event, NOTIFY too complex or + expensive, etc. + BAD - Command unknown, invalid, unsupported, or has + unknown arguments. + + + + + + +Gulbrandsen, et al. Standards Track [Page 4] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + + The NOTIFY command informs the server that the client listens for + event notifications all the time (even when no command is in + progress), and requests the server to notify it about the specified + set of events. The NOTIFY command has two forms. NOTIFY NONE + specifies that the client is not interested in any kind of event + happening on the server. NOTIFY SET replaces the current list of + interesting events with a new list of events. + + Until the NOTIFY command is used for the first time, the server only + sends notifications while a command is being processed, and notifies + the client about these events on the selected mailbox (see Section 5 + for definitions): MessageNew, MessageExpunge, or FlagChange. It does + not notify the client about any events on other mailboxes. + + The effect of a successful NOTIFY command lasts until the next NOTIFY + command or until the IMAP connection is closed. + + A successful NOTIFY SET command MUST cause the server to immediately + return any accumulated changes to the currently selected mailbox (if + any), such as flag changes and new or expunged messages. Thus, a + successful NOTIFY SET command implies an implicit NOOP command. + + The NOTIFY SET command can request notifications of message-related + changes to the selected mailbox, whatever that may be at the time the + message notifications are being generated. This is done by + specifying either the SELECTED or the SELECTED-DELAYED mailbox + selector (see Section 6.1) in the NOTIFY SET command. If the + SELECTED/SELECTED-DELAYED mailbox selector is not specified in the + NOTIFY SET command, this means that the client doesn't want to + receive any <message-event>s for the currently selected mailbox. + This is the same as specifying SELECTED NONE. + + The client can also request notifications on other mailboxes by name + or by a limited mailbox pattern match. Message-related notifications + returned for the currently selected mailbox will be those specified + by the SELECTED/SELECTED-DELAYED mailbox specifier, even if the + selected mailbox also appears by name (or matches a pattern) in the + command. Non-message-related notifications are controlled by mailbox + specifiers other than SELECTED/SELECTED-DELAYED. + + If the NOTIFY command enables MessageNew, MessageExpunge, + AnnotationChange, or FlagChange notifications for a mailbox other + than the currently selected mailbox, and the client has specified the + STATUS indicator parameter, then the server MUST send a STATUS + response for that mailbox before NOTIFY's tagged OK. If MessageNew + is enabled, the STATUS response MUST contain MESSAGES, UIDNEXT, and + UIDVALIDITY. If MessageExpunge is enabled, the STATUS response MUST + contain MESSAGES. If either AnnotationChange or FlagChange are + + + +Gulbrandsen, et al. Standards Track [Page 5] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + + included and the server also supports the CONDSTORE [RFC4551] and/or + QRESYNC [RFC5162] extensions, the STATUS response MUST contain + UIDVALIDITY and HIGHESTMODSEQ. Absence of the STATUS indicator + parameter allows the client to avoid the additional STATUS responses. + This might be useful if the client already retrieved this information + before issuing the NOTIFY command. + + Clients are advised to limit the number of mailboxes used with + NOTIFY. Particularly, if a client asks for events for all accessible + mailboxes, the server may swamp the client with updates about shared + mailboxes. This may reduce the client's battery life. Also, this + wastes both server and network resources. + + For each mailbox specified, the server verifies that the client has + access using the following test: + + - If the name does not refer to an existing mailbox, the server MUST + ignore it. + + - If the name refers to a mailbox that the client can't LIST, the + server MUST ignore it. For a server that implements [RFC4314], + this means that if the client doesn't have the 'l' (lookup) right + for the name, then the server MUST ignore the mailbox. This + behavior prevents disclosure of potentially confidential + information to clients who don't have rights to know it. + + - If the name refers to a mailbox that the client can LIST (e.g., it + has the 'l' right from [RFC4314]), but the client doesn't have + another right required for processing of the specified event(s), + then the server MUST respond with an untagged extended LIST + response containing the \NoAccess name attribute. + + The server SHOULD return the tagged OK response if the client has + access to at least one of the mailboxes specified in the current list + of interesting events. The server MAY return the tagged NO response + if the client has no access to any of the specified mailboxes and no + access can ever be granted in the future (e.g., the client specified + an event for 'Subtree Bar/Foo', 'Bar/Foo' doesn't exist, and LIST + returns \Noinferiors for the parent 'Bar'). + + If the notification would be prohibitively expensive for the server + (e.g., "notify me of all flag changes in all mailboxes"), the server + MAY refuse the command with a tagged NO [NOTIFICATIONOVERFLOW] + response. + + + + + + + +Gulbrandsen, et al. Standards Track [Page 6] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + + If the client requests information for events of an unsupported type, + the server MUST refuse the command with a tagged NO response (not a + BAD). This response SHOULD contain the BADEVENT response code, which + MUST list names of all events supported by the server. + + Here's an example: + + S: * OK [CAPABILITY IMAP4REV1 NOTIFY] + C: a login bob alice + S: a OK Password matched + C: b notify set status (selected MessageNew (uid + body.peek[header.fields (from to subject)]) MessageExpunge) + (subtree Lists MessageNew) + S: * STATUS Lists/Lemonade (UIDVALIDITY 4 UIDNEXT 9999 MESSAGES + 500) + S: [...] + S: * STATUS Lists/Im2000 (UIDVALIDITY 901 UIDNEXT 1 MESSAGES 0) + S: b OK done + C: c select inbox + S: [...] (the usual 7-8 responses to SELECT) + S: c OK INBOX selected + (Time passes. A new message is delivered to mailbox + Lists/Lemonade.) + S: * STATUS Lists/Lemonade (UIDVALIDITY 4 UIDNEXT 10000 + MESSAGES 501) + (Time passes. A new message is delivered to inbox.) + S: * 127 FETCH (UID 127001 BODY[HEADER.FIELDS (From To + Subject)] {75} + S: Subject: Re: good morning + S: From: alice@example.org + S: To: bob@example.org + S: + S: ) + (Time passes. The client decides it wants to know about + one more mailbox. As the client already knows necessary + STATUS information for all mailboxes below the Lists + mailbox, and because "notify set status" would cause + STATUS responses for *all* mailboxes specified in the + NOTIFY command, including the ones for which the client + already knows STATUS information, the client issues an + explicit STATUS request for the mailbox to be added to + the watch list, followed by the NOTIFY SET without the + STATUS parameter.) + C: d STATUS misc (UIDVALIDITY UIDNEXT MESSAGES) + S: * STATUS misc (UIDVALIDITY 1 UIDNEXT 999) + S: d STATUS completed + + + + + +Gulbrandsen, et al. Standards Track [Page 7] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + + C: e notify set (selected MessageNew (uid + body.peek[header.fields (from to subject)]) MessageExpunge) + (subtree Lists MessageNew) (mailboxes misc MessageNew) + S: e OK done + +4. Interaction with the IDLE Command + + If IDLE [RFC2177] (as well as this extension) is supported, then + while processing any IDLE command, the server MUST send exactly the + same events as instructed by the client using the NOTIFY command. + + NOTIFY makes IDLE unnecessary for some clients. If a client does not + use MSNs and '*' in commands, it can request MessageExpunge and + MessageNew for the selected mailbox by using the NOTIFY command + instead of entering the IDLE mode. + + A client that uses MSNs and '*' in commands can still use the NOTIFY + command if it specifies the SELECTED-DELAYED mailbox specifier in the + NOTIFY command. + +5. Event Types + + Only some of the events in [RFC5423] can be expressed in IMAP, and + for some of them there are several possible ways to express the + event. + + This section specifies the events of which an IMAP server can notify + an IMAP client, and how. + + The server SHOULD omit notifying the client if the event is caused by + this client. For example, if the client issues CREATE and has + requested a MailboxName event that would cover the newly created + mailbox, the server SHOULD NOT notify the client of the MailboxName + change. + + All event types described in this document require the 'l' and 'r' + rights (see [RFC4314]) on all observed mailboxes. Servers that don't + implement [RFC4314] should map the above rights to their access- + control model. + + If the FlagChange and/or AnnotationChange events are specified, + MessageNew and MessageExpunge MUST also be specified by the client. + Otherwise, the server MUST respond with the tagged BAD response. + + If one of MessageNew or MessageExpunge is specified, then both events + MUST be specified. Otherwise, the server MUST respond with the + tagged BAD response. + + + + +Gulbrandsen, et al. Standards Track [Page 8] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + + The client can instruct the server not to send an event by omitting + the necessary event from the list of events specified in NOTIFY SET, + by using the NONE event specifier in the NOTIFY SET, or by using + NOTIFY NONE. In particular, NOTIFY SET ... NONE can be used as a + snapshot facility by clients. + +5.1. FlagChange and AnnotationChange + + If the flag and/or message annotation change happens in the selected + mailbox, the server MUST notify the client by sending an unsolicited + FETCH response, which MUST include UID and FLAGS/ANNOTATION FETCH + data items. It MAY also send new FLAGS and/or OK [PERMANENTFLAGS + ...] responses. + + If a search context is in effect as specified in [RFC5267], an + ESEARCH ADDTO or ESEARCH REMOVEFROM will also be generated, if + appropriate. In this case, the FETCH response MUST precede the + ESEARCH response. + + If the change happens in another mailbox, then the server responds + with a STATUS response. The exact content of the STATUS response + depends on various factors. If CONDSTORE [RFC4551] and/or QRESYNC + [RFC5162] are enabled by the client, then the server sends a STATUS + response that includes at least HIGHESTMODSEQ and UIDVALIDITY status + data items. If the number of messages with the \Seen flag changes, + the server MAY also include the UNSEEN data item in the STATUS + response. If CONDSTORE/QRESYNC is not enabled by the client and the + server chooses not to include the UNSEEN data item, the server does + not notify the client. When this event is requested, the server MUST + notify the client about mailbox UIDVALIDITY changes. This is done by + sending a STATUS response that includes UIDVALIDITY. + + FlagChange covers the MessageRead, MessageTrash, FlagsSet, and + FlagsClear events in [RFC5423]. + + Example in the selected mailbox: + S: * 99 FETCH (UID 9999 FLAGS ($Junk)) + + And in another mailbox, with CONDSTORE in use: + S: * STATUS Lists/Lemonade (HIGHESTMODSEQ 65666665 UIDVALIDITY + 101) + + + + + + + + + + +Gulbrandsen, et al. Standards Track [Page 9] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + +5.2. MessageNew + + This covers both MessageNew and MessageAppend in [RFC5423]. + + If the new/appended message is in the selected mailbox, the server + notifies the client by sending an unsolicited EXISTS response, + followed by an unsolicited FETCH response containing the information + requested by the client. A FETCH response SHOULD NOT be generated + for a new message created by the client on this particular + connection, for instance, as the result of an APPEND or COPY command + to the selected mailbox performed by the client itself. The server + MAY also send a RECENT response, if the server marks the message as + \Recent. + + Note that a single EXISTS response can be returned for multiple + MessageAppend/MessageNew events. + + If a search context is in effect as specified in [RFC5267], an + ESEARCH ADDTO will also be generated, if appropriate. In this case, + the EXISTS response MUST precede the ESEARCH response. Both the + NOTIFY command and the SEARCH and SORT commands (see Section 7) can + specify attributes to be returned for new messages. These attributes + SHOULD be combined into a single FETCH response. The server SHOULD + avoid sending duplicate data. The FETCH response(s) MUST follow any + ESEARCH ADDTO responses. + + If the new/appended message is in another mailbox, the server sends + an unsolicited STATUS (UIDNEXT MESSAGES) response for the relevant + mailbox. If the CONDSTORE extension [RFC4551] and/or the QRESYNC + extension [RFC5162] is enabled, the HIGHESTMODSEQ status data item + MUST be included in the STATUS response. + + The client SHOULD NOT use FETCH attributes that implicitly set the + \seen flag, or that presuppose the existence of a given bodypart. + UID, MODSEQ, FLAGS, ENVELOPE, BODY.PEEK[HEADER.FIELDS... and + BODY/BODYSTRUCTURE may be the most useful attributes. + + Note that if a client asks to be notified of MessageNew events with + the SELECTED mailbox specifier, the number of messages can increase + at any time, and therefore the client cannot refer to a specific + message using the MSN/UID '*'. + + Example in the selected mailbox: + S: * 444 EXISTS + S: * 444 FETCH (UID 9999) + + And in another mailbox, without CONDSTORE enabled: + S: * STATUS Lists/Lemonade (UIDNEXT 10002 MESSAGES 503) + + + +Gulbrandsen, et al. Standards Track [Page 10] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + +5.3. MessageExpunge + + If the expunged message or messages are in the selected mailbox, the + server notifies the client using EXPUNGE (or VANISHED, if [RFC5162] + is supported by the server and enabled by the client). + + If a search context is in effect, as specified in [RFC5267], an + ESEARCH REMOVEFROM will also be generated, if appropriate. + + If the expunged message or messages are in another mailbox, the + server sends an unsolicited STATUS (UIDNEXT MESSAGES) response for + the relevant mailbox. If the QRESYNC [RFC5162] extension is enabled, + the HIGHESTMODSEQ data item MUST be included in the STATUS response + as well. + + Note that if a client requests MessageExpunge with the SELECTED + mailbox specifier, the meaning of an MSN can change at any time, so + the client cannot use MSNs in commands anymore. For example, such a + client cannot use FETCH, but has to use UID FETCH. The meaning of + '*' can also change when messages are added or expunged. A client + wishing to keep using MSNs can either use the SELECTED-DELAYED + mailbox specifier or can avoid using the MessageExpunge event + entirely. + + The MessageExpunge notification covers both MessageExpunge and + MessageExpire events from [RFC5423]. + + Example in the selected mailbox, without QRESYNC: + S: * 444 EXPUNGE + + The same example in the selected mailbox, with QRESYNC: + S: * VANISHED 5444 + + And in another mailbox, when QRESYNC is not enabled: + S: * STATUS misc (UIDNEXT 999 MESSAGES 554) + +5.4. MailboxName + + These notifications are sent if an affected mailbox name was created + (with CREATE), deleted (with DELETE), or renamed (with RENAME). For + a server that implements [RFC4314], granting or revocation of the 'l' + right to the current user on the affected mailbox MUST be considered + mailbox creation or deletion, respectively. If a mailbox is created + or deleted, the mailbox itself and its direct parent (whether it is + an existing mailbox or not) are considered to be affected. + + + + + + +Gulbrandsen, et al. Standards Track [Page 11] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + + The server notifies the client by sending an unsolicited LIST + response for each affected mailbox name. If, after the event, the + mailbox name does not refer to a mailbox accessible to the client, + the \Nonexistent flag MUST be included. + + For each LISTable mailbox renamed, the server sends an extended LIST + response [RFC5258] for the new mailbox name, containing the OLDNAME + extended data item with the old mailbox name. When a mailbox is + renamed, its children are renamed too. No additional MailboxName + events are sent for children in this case. When INBOX is renamed, a + new INBOX is assumed to be created. No MailboxName event is sent for + INBOX in this case. + + If the server automatically subscribes a mailbox when it is created + or renamed, then the unsolicited LIST response for each affected + subscribed mailbox name MUST include the \Subscribed attribute (see + [RFC5258]). The server SHOULD also include \HasChildren or + \HasNoChildren attributes [RFC5258] as appropriate. + + Example of a newly created mailbox (or granting of the 'l' right on + the mailbox): + S: * LIST () "/" "NewMailbox" + + And a deleted mailbox (or revocation of the 'l' right on the + mailbox): + S: * LIST (\NonExistent) "." "INBOX.DeletedMailbox" + + Example of a renamed mailbox: + S: * LIST () "/" "NewMailbox" ("OLDNAME" ("OldMailbox")) + +5.5. SubscriptionChange + + The server notifies the client by sending an unsolicited LIST + response for each affected mailbox name. If and only if the mailbox + is subscribed after the event, the \Subscribed attribute (see + [RFC5258]) is included. Note that in the LIST response, all mailbox + attributes MUST be accurately computed (this differs from the + behavior of the LSUB command). + + Example: + S: * LIST (\Subscribed) "/" "SubscribedMailbox" + +5.6. MailboxMetadataChange + + Support for this event type is OPTIONAL unless the METADATA extension + [RFC5464] is also supported by the server, in which case support for + this event type is REQUIRED. + + + + +Gulbrandsen, et al. Standards Track [Page 12] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + + A client willing to receive unsolicited METADATA responses as a + result of using the MailboxMetadataChange event in the NOTIFY command + doesn't have to issue ENABLE METADATA. + + The server sends an unsolicited METADATA response (as per Section + 4.4.2 of [RFC5464]). If possible, only the changed metadata SHOULD + be included, but if the server can't detect a change to a single + metadata item, it MAY include all metadata items set on the mailbox. + If a metadata item is deleted (set to NIL), it MUST always be + included in the METADATA response. + + Example: + S: * METADATA "INBOX" /shared/comment + +5.7. ServerMetadataChange + + Support for this event type is OPTIONAL unless the METADATA or the + METADATA-SERVER extension [RFC5464] is also supported by the server, + in which case support for this event type is REQUIRED. + + A client willing to receive unsolicited METADATA responses as a + result of using the ServerMetadataChange event in the NOTIFY command + doesn't have to issue ENABLE METADATA or ENABLE METADATA-SERVER. + + The server sends an unsolicited METADATA response (as per Section + 4.4.2 of [RFC5464]). Only the names of changed metadata entries + SHOULD be returned in such METADATA responses. If a metadata item is + deleted (set to NIL), it MUST always be included in the METADATA + response. + + Example: + S: * METADATA "" /shared/comment + +5.8. Notification Overflow + + If the server is unable or unwilling to deliver as many notifications + as it is being asked to, it may disable notifications for some or all + clients. It MUST notify these clients by sending an untagged "OK + [NOTIFICATIONOVERFLOW]" response and behave as if a NOTIFY NONE + command had just been received. + + Example: + S: * OK [NOTIFICATIONOVERFLOW] ...A comment can go here... + + + + + + + + +Gulbrandsen, et al. Standards Track [Page 13] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + +5.9. ACL (Access Control List) Changes + + Even if NOTIFY succeeds, it is still possible to lose access to the + mailboxes being monitored at a later time. If this happens, the + server MUST stop monitoring these mailboxes. If access is later + granted, the server MUST restart event monitoring. + + The server SHOULD return the LIST response with the \NoAccess name + attribute if and when the mailbox loses the 'l' right. Similarly, + the server SHOULD return the LIST response with no \NoAccess name + attribute if the mailbox was previously reported as having \NoAccess + and the 'l' right is later granted. + +6. Mailbox Specification + + Mailboxes to be monitored can be specified in several different ways. + + Only 'SELECTED' and 'SELECTED-DELAYED' (Section 6.1) match the + currently selected mailbox. All other mailbox specifications affect + other (non-selected) mailboxes. + + Note that multiple <event-group>s can apply to the same mailbox. The + following example demonstrates this. In this example, MessageNew and + MessageExpunge events are reported for INBOX, due to the first + <event-group>. A SubscriptionChange event will also be reported for + INBOX, due to the second <event-group>. + + C: a notify set (mailboxes INBOX (Messagenew messageExpunge)) + (personal (SubscriptionChange)) + + A typical client that supports the NOTIFY extension would ask for + events on the selected mailbox and some named mailboxes. + + In the next example, the client asks for FlagChange events for all + personal mailboxes except the currently selected mailbox. This is + different from the previous example because SELECTED overrides all + other message event definitions for the currently selected mailbox + (see Section 3.1). + + C: a notify set (selected (Messagenew (uid flags) messageExpunge)) + (personal (MessageNew FlagChange MessageExpunge)) + +6.1. Mailbox Specifiers Affecting the Currently Selected Mailbox + + Only one of the mailbox specifiers affecting the currently selected + mailbox can be specified in any NOTIFY command. The two such mailbox + specifiers (SELECTED and SELECTED-DELAYED) are described below. + + + + +Gulbrandsen, et al. Standards Track [Page 14] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + + Both refer to the mailbox that was selected using either SELECT or + EXAMINE (see [RFC3501], Sections 6.3.1 and 6.3.2). When the IMAP + connection is not in the selected state, such mailbox specifiers + don't refer to any mailbox. + + The mailbox specifiers only apply to <message-event>s. It is an + error to specify other types of events with either the SELECTED or + the SELECTED-DELAYED selector. + +6.1.1. Selected + + The SELECTED mailbox specifier requires the server to send immediate + notifications for the currently selected mailbox about all specified + <message-event>s. + +6.1.2. Selected-Delayed + + The SELECTED-DELAYED mailbox specifier requires the server to delay a + MessageExpunge event until the client issues a command that allows + returning information about expunged messages (see Section 7.4.1 of + [RFC3501] for more details), for example, till a NOOP or an IDLE + command has been issued. When SELECTED-DELAYED is specified, the + server MAY also delay returning other <message-event>s until the + client issues one of the commands specified above, or it MAY return + them immediately. + +6.2. Personal + + Personal refers to all selectable mailboxes in the user's personal + namespace(s), as defined in [RFC2342]. + +6.3. Inboxes + + Inboxes refers to all selectable mailboxes in the user's personal + namespace(s) to which messages may be delivered by a Message Delivery + Agent (MDA) (see [EMAIL-ARCH], particularly Section 4.3.3). + + If the IMAP server cannot easily compute this set, it MUST treat + "inboxes" as equivalent to "personal". + +6.4. Subscribed + + Subscribed refers to all mailboxes subscribed to by the user. + + If the subscription list changes, the server MUST reevaluate the + list. + + + + + +Gulbrandsen, et al. Standards Track [Page 15] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + +6.5. Subtree + + Subtree is followed by a mailbox name or list of mailbox names. A + subtree refers to all selectable mailboxes that are subordinate to + the specified mailbox plus the specified mailbox itself. + +6.6. Mailboxes + + Mailboxes is followed by a mailbox name or a list of mailbox names. + The server MUST NOT do a wildcard expansion. This means there is no + special treatment for the LIST wildcard characters ('*' and '%') if + they are present in mailbox names. + +7. Extension to SEARCH and SORT Commands + + If the server that supports the NOTIFY extension also supports + CONTEXT=SEARCH and/or CONTEXT=SORT as defined in [RFC5267], the + UPDATE return option is extended so that a client can request that + FETCH attributes be returned when a new message is added to the + context result set. + + For example: + + C: a00 SEARCH RETURN (COUNT UPDATE (UID BODY[HEADER.FIELDS (TO + FROM SUBJECT)])) FROM "boss" + S: * ESEARCH (TAG "a00") (COUNT 17) + S: a00 OK + [...a new message is delivered...] + S: * EXISTS 93 + S: * 93 FETCH (UID 127001 BODY[HEADER.FIELDS (FROM TO SUBJECT)] + {76} + S: Subject: Re: good morning + S: From: myboss@example.org + S: To: bob@example.org + S: + S: ) + S: * ESEARCH (TAG "a00") ADDTO (0 93) + + Note that the EXISTS response MUST precede any FETCH responses, and + together they MUST precede the ESEARCH response. + + No untagged FETCH response SHOULD be returned if a message becomes a + member of UPDATE SEARCH due to flag or annotation changes. + + + + + + + + +Gulbrandsen, et al. Standards Track [Page 16] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + +8. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [RFC5234]. [RFC3501] defines + the non-terminals "capability", "command-auth", "mailbox", "mailbox- + data", "resp-text-code", and "search-key". The "modifier-update" + non-terminal is defined in [RFC5267]. "mbx-list-oflag" is defined in + [RFC3501] and updated by [RFC5258]. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper or lower case characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. For example, the + <filter-mailboxes-selected> non-terminal value "SELECTED" must be + treated in the same way as "Selected" or "selected". + + capability =/ "NOTIFY" + + command-auth =/ notify + + notify = "NOTIFY" SP + (notify-set / notify-none) + + notify-set = "SET" [status-indicator] SP event-groups + ; Replace registered notification events + ; with the specified list of events + + notify-none = "NONE" + ; Cancel all registered notification + ; events. The client is not interested + ; in receiving any events. + + status-indicator = SP "STATUS" + + one-or-more-mailbox = mailbox / many-mailboxes + + many-mailboxes = "(" mailbox *(SP mailbox) ")" + + event-groups = event-group *(SP event-group) + + event-group = "(" filter-mailboxes SP events ")" + ;; Only <message-event>s are allowed in <events> + ;; when <filter-mailboxes-selected> is used. + + filter-mailboxes = filter-mailboxes-selected / + filter-mailboxes-other + + + + + +Gulbrandsen, et al. Standards Track [Page 17] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + + filter-mailboxes-other = "inboxes" / "personal" / "subscribed" / + ( "subtree" SP one-or-more-mailbox ) / + ( "mailboxes" SP one-or-more-mailbox ) + + filter-mailboxes-selected = "selected" / "selected-delayed" + ;; Apply to the currently selected mailbox only. + ;; Only one of them can be specified in a NOTIFY + ;; command. + + events = ( "(" event *(SP event) ")" ) / "NONE" + ;; As in [MSGEVENT]. + ;; "NONE" means that the client does not wish + ;; to receive any events for the specified + ;; mailboxes. + + event = message-event / + mailbox-event / user-event / event-ext + + message-event = ( "MessageNew" [SP + "(" fetch-att *(SP fetch-att) ")" ] ) + / "MessageExpunge" + / "FlagChange" + / "AnnotationChange" + ;; "MessageNew" includes "MessageAppend" from + ;; [MSGEVENT]. "FlagChange" is any of + ;; "MessageRead", "MessageTrash", "FlagsSet", + ;; "FlagsClear" [MSGEVENT]. "MessageExpunge" + ;; includes "MessageExpire" [MSGEVENT]. + ;; MessageNew and MessageExpunge MUST always + ;; be specified together. If FlagChange is + ;; specified, then MessageNew and MessageExpunge + ;; MUST be specified as well. + ;; The fett-att list may only be present for the + ;; SELECTED/SELECTED-DELAYED mailbox filter + ;; (<filter-mailboxes>). + + mailbox-event = "MailboxName" / + "SubscriptionChange" / "MailboxMetadataChange" + ; "SubscriptionChange" includes + ; MailboxSubscribe and MailboxUnSubscribe. + ; "MailboxName" includes MailboxCreate, + ; "MailboxDelete" and "MailboxRename". + + user-event = "ServerMetadataChange" + + event-ext = atom + ;; For future extensions + + + + +Gulbrandsen, et al. Standards Track [Page 18] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + + oldname-extended-item = "OLDNAME" SP "(" mailbox ")" + ;; Extended data item (mbox-list-extended-item) + ;; returned in a LIST response when a mailbox is + ;; renamed. + ;; Note 1: the OLDNAME tag can be returned + ;; with or without surrounding quotes, as per + ;; mbox-list-extended-item-tag production. + + resp-text-code =/ "NOTIFICATIONOVERFLOW" / + unsupported-events-code + + message-event-name = "MessageNew" / + "MessageExpunge" / "FlagChange" / + "AnnotationChange" + + event-name = message-event-name / mailbox-event / + user-event + + unsupported-events-code = "BADEVENT" + SP "(" event-name *(SP event-name) ")" + + modifier-update = "UPDATE" + [ "(" fetch-att *(SP fetch-att) ")" ] + + mbx-list-oflag =/ "\NoAccess" + +9. Security Considerations + + It is very easy for a client to deny itself service using NOTIFY. + Asking for all events on all mailboxes may work on a small server, + but with a big server, can swamp the client's network connection or + processing capability. In the worst case, the server's processing + could also degrade the service it offers to other clients. + + Server authors should be aware that if a client issues requests and + does not listen to the resulting responses, the TCP window can easily + fill up, and a careless server might block. This problem also exists + in plain IMAP; however, this extension magnifies the problem. + + This extension makes it possible to retrieve messages immediately + when they are added to the mailbox. This makes it wholly impractical + to delete sensitive messages using programs like imapfilter. Using + SIEVE [RFC5228] or similar is much better. + + + + + + + + +Gulbrandsen, et al. Standards Track [Page 19] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + +10. IANA Considerations + + The IANA has added NOTIFY to the list of IMAP extensions. + +10.1. Initial LIST-EXTENDED Extended Data Item Registrations + + The following entry has been added to the LIST-EXTENDED response + registry [RFC5258]: + + To: iana@iana.org + Subject: Registration of OLDNAME LIST-EXTENDED extended data item + + LIST-EXTENDED extended data item tag: OLDNAME + + LIST-EXTENDED extended data item description: The OLDNAME extended + data item describes the old mailbox name for the mailbox + identified by the LIST response. + + Which LIST-EXTENDED option(s) (and their types) causes this extended + data item to be returned (if any): none + + Published specification : RFC 5465, Section 5.4. + + Security considerations: none + + Intended usage: COMMON + + Person and email address to contact for further information: Alexey + Melnikov <Alexey.Melnikov@isode.com> + + Owner/Change controller: iesg@ietf.org + +11. Acknowledgments + + The authors gratefully acknowledge the help of Peter Coates, Dave + Cridland, Mark Crispin, Cyrus Daboo, Abhijit Menon-Sen, Timo + Sirainen, and Eric Burger. In particular, Peter Coates contributed + lots of text and useful suggestions to this document. + + Various examples are copied from other RFCs. + + This document builds on one published and two unpublished drafts by + the same authors. + + + + + + + + +Gulbrandsen, et al. Standards Track [Page 20] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + +12. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2177] Leiba, B., "IMAP4 IDLE command", RFC 2177, June 1997. + + [RFC2342] Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342, + May 1998. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL) + Extension", RFC 4314, December 2005. + + [RFC4466] Melnikov, A. and C. Daboo, "Collected Extensions to + IMAP4 ABNF", RFC 4466, April 2006. + + [RFC4551] Melnikov, A. and S. Hole, "IMAP Extension for + Conditional STORE Operation or Quick Flag Changes + Resynchronization", RFC 4551, June 2006. + + [RFC5162] Melnikov, A., Cridland, D., and C. Wilson, "IMAP4 + Extensions for Quick Mailbox Resynchronization", RFC + 5162, March 2008. + + [RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", STD 68, RFC 5234, January + 2008. + + [RFC5258] Leiba, B. and A. Melnikov, "Internet Message Access + Protocol version 4 - LIST Command Extensions", RFC 5258, + June 2008. + + [RFC5267] Cridland, D. and C. King, "Contexts for IMAP4", RFC + 5267, July 2008. + + [RFC5423] Newman, C. and R. Gellens, "Internet Message Store + Events", RFC 5423, Month 2009. + + [RFC5464] Daboo, C., "The IMAP METADATA Extension", RFC 5464, + February 2009. + +13. Informative References + + [RFC5228] Guenther, P., Ed., and T. Showalter, Ed., "Sieve: An + Email Filtering Language", RFC 5228, January 2008. + + + +Gulbrandsen, et al. Standards Track [Page 21] + +RFC 5465 IMAP NOTIFY Extension February 2009 + + + [EMAIL-ARCH] Crocker, D., "Internet Mail Architecture", Work in + Progress, October 2008. + +Authors' Addresses + + Arnt Gulbrandsen + Oryx Mail Systems GmbH + Schweppermannstr. 8 + D-81671 Muenchen + Germany + + EMail: arnt@oryx.com + + + Curtis King + Isode Ltd + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: Curtis.King@isode.com + + + Alexey Melnikov + Isode Ltd + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: Alexey.Melnikov@isode.com + + + + + + + + + + + + + + + + + + + +Gulbrandsen, et al. Standards Track [Page 22] + diff --git a/imap/docs/rfc/rfc5466.txt b/imap/docs/rfc/rfc5466.txt new file mode 100644 index 00000000..d566a5f5 --- /dev/null +++ b/imap/docs/rfc/rfc5466.txt @@ -0,0 +1,507 @@ + + + + + + +Network Working Group A. Melnikov +Request for Comments: 5466 C. King +Category: Standards Track Isode Ltd + February 2009 + + + IMAP4 Extension for Named Searches (Filters) + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (c) 2009 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents (http://trustee.ietf.org/ + license-info) in effect on the date of publication of this document. + Please review these documents carefully, as they describe your rights + and restrictions with respect to this document. + +Abstract + + The document defines a way to persistently store named IMAP (RFC + 3501) searches on the server. Such named searches can be + subsequently referenced in a SEARCH or any other command that accepts + a search criterion as a parameter. + +Table of Contents + + 1. Introduction and Overview . . . . . . . . . . . . . . . . . . . 2 + 2. Conventions Used in This Document . . . . . . . . . . . . . . . 2 + 3. IMAP Protocol Changes . . . . . . . . . . . . . . . . . . . . . 2 + 3.1. FILTER SEARCH Criterion . . . . . . . . . . . . . . . . . . 3 + 3.2. Managing Filters Using SETMETADATA/GETMETADATA Commands . . 4 + 4. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 6 + 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 + 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 + 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8 + 8. Normative References . . . . . . . . . . . . . . . . . . . . . 8 + + + + + +Melnikov & King Standards Track [Page 1] + +RFC 5466 IMAP Filters February 2009 + + +1. Introduction and Overview + + Persistent named searches described in this document allow clients to + save favorite searches on the server. Such saved searches can save + bandwidth for clients that need to regularly repeat them. + + The FILTERS IMAP extension adds a new FILTER search criterion for + referencing persistent named searches (a.k.a. "filters"), as well as + reuses GETMETADATA/SETMETADATA commands [METADATA] for listing/ + creating/updating/deleting such filters. + + A filter can be private (only accessible to the logged-in user) or + public (accessible to all logged-in users). Both a private and a + public filter with the same name can exist at the same time. If both + filter types with the same name exist, the FILTER SEARCH criterion + (see Section 3.1) MUST use the value of the private filter; + otherwise, it MUST use the value of the filter that exists. + + Let us call a pair of filter name and filter type a "typed filter". + Each typed filter can have a value (which is a valid IMAP SEARCH + criteria conforming to ABNF for the "search-criteria" non-terminal) + and an optional human-readable description. The SETMETADATA command + creates or updates the value and/or the description of a typed + filter. + + Values of all search keys stored in a filter MUST be encoded in + UTF-8. + +2. Conventions Used in This Document + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. If a single "C:" or "S:" label applies to + multiple lines, then the line breaks between those lines are for + editorial clarity only and are not part of the actual protocol + exchange. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. + + Basic familiarity with the METADATA-SERVER extension [METADATA] and + terms defined therein is required to understand this document. + +3. IMAP Protocol Changes + + The IMAP extension for persistent named searches is present in any + IMAP4 implementation that advertises "FILTERS" as one of the + supported capabilities in the CAPABILITY response or response code. + + + +Melnikov & King Standards Track [Page 2] + +RFC 5466 IMAP Filters February 2009 + + +3.1. FILTER SEARCH Criterion + + The FILTER criterion for the SEARCH command allows a client to + reference by name a filter stored on the server. Such filter was + created by setting the server annotation named "/private/filters/ + values/<filter_name>" (or the server annotation "/shared/filters/ + values/<filter_name>", if "/private/filters/values/<filter_name>" + doesn't exist) using the SETMETADATA command as described in + Section 3.2. + + Syntax: FILTER <filter_name> + + When the named filter exists, its search criterion (i.e., the + associated entry value) is inserted verbatim instead of the FILTER + search-key. For example, the following SEARCH command + + C: a SEARCH UID 300:900 FILTER on-the-road SINCE "3-Dec-2002" + + would be equivalent to the following + + C: a SEARCH UID 300:900 OR SMALLER 5000 FROM "boss@example.com" + SINCE "3-Dec-2002" + + assuming the filter "on-the-road" exists and contains the value 'OR + SMALLER 5000 FROM "boss@example.com"'. + + A reference to a nonexistent or unaccessible (e.g., due to access + control restrictions) filter MUST cause failure of the SEARCH command + with the tagged NO response that includes the UNDEFINED-FILTER + response code followed by the name of the nonexistent/unaccessible + filter. + + Note the server SHOULD verify that each search criterion referenced + by the FILTER search key is a full and correct search criterion. For + example, the server should fail the SEARCH command if its SEARCH + criterion references a filter containing "OR SMALLER" search + criterion, because this value is lacking one parameter and thus is + not a fully specified search criterion. + + Note that a named filter itself can reference another filter using + the FILTER search-key. Implementations MUST be able to perform at + least 3 substitution passes on the SEARCH command criterion. If an + implementation allows for more passes, it MUST implement some kind of + loop detection. If an implementation detects a loop or still sees a + FILTER search-key after performing at least 3 substitutions, it MUST + behave as if the specified filter doesn't exist (as described above). + + + + + +Melnikov & King Standards Track [Page 3] + +RFC 5466 IMAP Filters February 2009 + + + Note that use of the FILTER search key implies the CHARSET "UTF-8" + parameter to the SEARCH/UID SEARCH command. If the SEARCH/UID SEARCH + command includes the explicit CHARSET parameter with the value other + than "UTF-8" or "US-ASCII", then such command MUST result in the + tagged BAD response from the server. Such tagged response MUST + contain the BADCHARSET response code (see [RFC3501]). + +3.2. Managing Filters Using SETMETADATA/GETMETADATA Commands + + Any server compliant with this document MUST either implement the + METADATA-SERVER (or METADATA) [METADATA] extension, or implement + SETMETADATA/GETMETADATA commands described in [METADATA] so that they + work for the case of empty mailbox name (i.e., for managing server + annotations) and for the entries specified in this section. + + This document reserves two hierarchies of per-server entries under + the "/private/filters/values" and "/shared/filters/values" roots (see + [METADATA]) for storing filter values. The value of a "/private/ + filters/values/<filter_name>" or a "/shared/filters/values/ + <filter_name>" server annotation is an IMAP SEARCH criteria, + conforming to ABNF for the "search-criteria" non-terminal. A name of + a filter is governed by the ABNF for the "filter-name" non-terminal. + + Note that values of all search keys stored in these entries MUST be + encoded in UTF-8. + + A new filter named "<filter_name>" can be created (or an existing + filter can be modified) by storing a non-NIL value in the "/private/ + filters/values/<filter_name>" server entry (or in the "/shared/ + filters/values/<filter_name>") using the SETMETADATA [METADATA] + command. The server SHOULD verify that each search criterion stored + in such a server entry is a full and correct search criterion. + + A filter can be deleted by storing the NIL value in both the + "/private/filters/values/<filter_name>" and the "/shared/filters/ + values/<filter_name>" entries. + + A filter can be renamed by first creating a filter with the new name + (that has the same value as the old one) and then deleting the filter + with the old one. + + If both "/private/filters/values/<filter_name>" and "/shared/filters/ + values/<filter_name>" server annotations exist, then the value of the + "/private/filters/values/<filter_name>" is used when evaluating the + corresponding FILTER SEARCH key (see Section 3.1). Otherwise the + non-NIL (existent) value is used. + + + + + +Melnikov & King Standards Track [Page 4] + +RFC 5466 IMAP Filters February 2009 + + + If the server is unable to create a new typed filter because the + maximum number of allowed filters has already been reached, the + server MUST return a tagged NO response with a "[METADATA TOOMANY]" + response code, as defined in [METADATA]. + + C: a007 SETMETADATA "" ("/private/filters/values/on-the-road" + "OR SMALLER 5000 FROM \"boss@example.com\"") + S: a007 OK SETMETADATA complete + + Client implementation note: As multiple clients might read and write + filter values, it is possible that one client will use a SEARCH key + that might not be recognized by another client that tries to present + a user interface for editing a filter value. In order to help other + clients to (partially) parse filter values for editing purposes, a + client storing a filter value SHOULD use () around any SEARCH key not + defined in [RFC3501]. For example, if there is an IMAP extension + that defines a new x-dsfa SEARCH key that takes 2 parameters, then + the following SEARCH criterion 'from "@example.com>" x-dsfa from 5' + should be stored as 'from "@example.com>" (x-dsfa from 5)'. + + Note that filter names are restricted to a subset of US-ASCII, as + described in Section 4. So they might not always be meaningful to + users and thus not necessarily suitable for display purposes. In + order to help with storing human-readable descriptions of filters, + this document also reserves two hierarchies of server entries under + the "/private/filters/descriptions" and "/shared/filters/ + descriptions" roots. The value of a "/private/filters/descriptions/ + <filter_name>" or a "/shared/filters/descriptions/<filter_name>" + server annotation is a human-readable description for the + <filter_name> filter, encoded in UTF-8 [UTF-8]. If the "/private/ + filters/descriptions/<filter_name>" server annotation exists, its + value is used by the client as the filter description. Otherwise, + the value of the "/shared/filters/descriptions/<filter_name>" server + annotation is used as the filter description. In the absence of both + the "/private/filters/descriptions/<filter_name>" and the "/shared/ + filters/descriptions/<filter_name>" entries, the client MAY display + the name of the filter as its description. + + The description string SHOULD be annotated with one or more language + tags [RFC4646] as specified in Chapter 16.9 of [Unicode]. In the + absence of any language tag, the "i-default" [RFC2277] language + SHOULD be assumed. Description in multiple languages MAY be present + in a single description string. This is done by concatenating + descriptions in multiple languages into a single string, each + description prefixed with its language tag, for example + "<ru><...description in Russian...><fr-ca><...description in + French...>". Note that here <ru> is a language tag consisting of 3 + Unicode characters: <U+E0001>, <U+E0072>, <U+E0075>; and <fr-ca> is a + + + +Melnikov & King Standards Track [Page 5] + +RFC 5466 IMAP Filters February 2009 + + + language tag consisting of 6 Unicode characters: <U+E0001>, + <U+E0066>, <U+E0072>, <U+E002D>, <U+E0063>, <U+E0061>. + +4. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [ABNF]. + + Non-terminals referenced but not defined below are as defined by + [RFC3501] or [IMAPABNF]. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper or lower case characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + capability =/ "FILTERS" + + search-criteria = search-key *(SP search-key) + + search-key =/ "FILTER" SP filter-name + ;; New SEARCH criterion for referencing filters + + filter-name = 1*<any ATOM-CHAR except "/"> + ;; Note that filter-name disallows UTF-8 or + ;; the following characters: "(", ")", "{", + ;; " ", "%", "*", "]". See definition of + ;; ATOM-CHAR [RFC3501]. + + resp-text-code =/ "UNDEFINED-FILTER" SP filter-name + +5. Security Considerations + + General issues relevant to [RFC3501] (in particular to the SEARCH + command) and METADATA-SERVER extension [METADATA] are also relevant + to this document. + + Note that excessive use of filters can potentially simplify denial- + of-service attacks, especially if combined with poor implementations + and lack of loop detection (i.e., detection of filters referencing + each other to create a loop). Servers that allow for anonymous + access SHOULD NOT allow anonymous users to create/edit/delete + filters. + + Also note that stored filters can potentially disclose personal + information about users. When confidentiality of such information is + important, clients MUST use TLS and/or SASL security layer (or + similar) as recommended in [RFC3501]. Also, clients should use + + + +Melnikov & King Standards Track [Page 6] + +RFC 5466 IMAP Filters February 2009 + + + private filters instead of public, unless they desire to share such + information with other users. + + As always, it is important to thoroughly test clients and servers + when implementing this extension. + +6. IANA Considerations + + IMAP4 capabilities are registered by publishing a Standards Track or + IESG-approved Experimental RFC. The IMAP4 capabilities registry is + available from http://www.iana.org. + + This document defines the FILTERS IMAP capability. IANA has added it + to the registry. + + IANA has added the following 4 entries to the [METADATA] registry: + + To: iana@iana.org + Subject: IMAP METADATA Entry Registration + Type: Server + Name: /private/filters/values/<filter_name> + Description: Contains an IMAP SEARCH criteria. Defined in RFC 5466. + Content-type: text/plain; charset=utf-8 + Contact person: Alexey Melnikov + Email: alexey.melnikov@isode.com + + To: iana@iana.org + Subject: IMAP METADATA Entry Registration + Type: Server + Name: /shared/filters/values/<filter_name> + Description: Contains an IMAP SEARCH criterion. Defined in RFC + 5466. + Content-type: text/plain; charset=utf-8 + Contact person: Alexey Melnikov + Email: alexey.melnikov@isode.com + + To: iana@iana.org + Subject: IMAP METADATA Entry Registration + Type: Server + Name: /private/filters/descriptions/<filter_name> + Description: Contains a user-specific human-readable description of + a named SEARCH criterion stored in the /private/filters/values/ + <filter_name> or /shared/filters/values/<filter_name> annotation. + The value is in UTF-8. Defined in RFC 5466. + Content-type: text/plain; charset=utf-8 + Contact person: Alexey Melnikov + Email: alexey.melnikov@isode.com + + + + +Melnikov & King Standards Track [Page 7] + +RFC 5466 IMAP Filters February 2009 + + + To: iana@iana.org + Subject: IMAP METADATA Entry Registration + Type: Server + Name: /shared/filters/descriptions/<filter_name> + Description: Contains a global (shared among all users) human- + readable description of a named SEARCH criterion stored in the + /private/filters/values/<filter_name> or /shared/filters/values/ + <filter_name> annotation. The value is in UTF-8. Defined in RFC + 5466. + Content-type: text/plain; charset=utf-8 + Contact person: Alexey Melnikov + Email: alexey.melnikov@isode.com + +7. Acknowledgments + + Thanks to David Cridland, Arnt Gulbrandsen, Chris Newman, and Timo + Sirainen for comments and suggestions on this document. Special + thank you to Brian E. Carpenter for the GenArt review. + +8. Normative References + + [ABNF] Crocker, D., Ed. and P. Overell, Ed., "Augmented BNF for + Syntax Specifications: ABNF", STD 68, RFC 5234, + January 2008. + + [IMAPABNF] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4 + ABNF", RFC 4466, April 2006. + + [METADATA] Daboo, C., "The IMAP METADATA Extension", RFC 5464, + February 2009. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and + Languages", BCP 18, RFC 2277, January 1998. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [RFC4646] Phillips, A. and M. Davis, "Tags for Identifying + Languages", BCP 47, RFC 4646, September 2006. + + [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO + 10646", STD 63, RFC 3629, November 2003. + + [Unicode] "The Unicode Standard 5.0", Unicode 5.0, 2007, + <http://www.unicode.org/versions/Unicode5.0.0/>. + + + +Melnikov & King Standards Track [Page 8] + +RFC 5466 IMAP Filters February 2009 + + +Authors' Addresses + + Alexey Melnikov + Isode Ltd + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: Alexey.Melnikov@isode.com + + + Curtis King + Isode Ltd + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: Curtis.King@isode.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov & King Standards Track [Page 9] + diff --git a/imap/docs/rfc/rfc5524.txt b/imap/docs/rfc/rfc5524.txt new file mode 100644 index 00000000..3808d1ff --- /dev/null +++ b/imap/docs/rfc/rfc5524.txt @@ -0,0 +1,507 @@ + + + + + + +Network Working Group D. Cridland +Request for Comments: 5524 Isode Limited +Category: Standards Track May 2009 + + + Extended URLFETCH for Binary and Converted Parts + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (c) 2009 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents in effect on the date of + publication of this document (http://trustee.ietf.org/license-info). + Please review these documents carefully, as they describe your rights + and restrictions with respect to this document. + +Abstract + + The URLFETCH command defined as part of URLAUTH provides a mechanism + for third parties to gain access to data held within messages in a + user's private store; however, this data is sent verbatim, which is + not suitable for a number of applications. This memo specifies a + method for obtaining data in forms suitable for non-mail + applications. + + + + + + + + + + + + + + + + + +Cridland Standards Track [Page 1] + +RFC 5524 URLFETCH Binary May 2009 + + +Table of Contents + + 1. Introduction ....................................................2 + 2. Conventions Used in This Document ...............................2 + 3. Extended URLFETCH ...............................................2 + 3.1. Command Parameters .........................................3 + 3.2. Response Metadata ..........................................3 + 4. Example Exchanges ...............................................4 + 5. Formal Syntax ...................................................6 + 6. IANA Considerations .............................................7 + 7. Security Considerations .........................................7 + 8. Acknowledgements ................................................7 + 9. References ......................................................8 + 9.1. Normative References .......................................8 + 9.2. Informative References .....................................8 + +1. Introduction + + Although [URLAUTH] provides a URLFETCH command that can be used to + dereference a URL and return the body-part data, it does so by + returning the encoded form, without sufficient metadata to decode. + This is suitable for use in mail applications such as [BURL], where + the encoded form is suitable, but not where access to the actual + content is required, such as in [STREAMING]. + + This memo specifies a mechanism that returns additional metadata + about the part, such as its [MEDIATYPE] type, as well as removes any + content transfer encoding that was used on the body part. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [KEYWORDS]. + + Protocol examples are line-wrapped for clarity. Protocol strings are + prefixed with C: and S: for client and server respectively, and + elided data is represented by [...]. Implementors should note these + notations are for editorial clarity only. + +3. Extended URLFETCH + + This extension is available in any IMAP server implementation that + includes URLAUTH=BINARY within its capability string. + + Such servers accept additional, per-URL parameters to the URLFETCH + command and will provide, upon request, specific data for each URL + dereferenced. + + + +Cridland Standards Track [Page 2] + +RFC 5524 URLFETCH Binary May 2009 + + +3.1. Command Parameters + + The URLFETCH command is extended by the provision of optional + parameters. The extended URLFETCH command is distinct by enclosing + each URL and associated parameters in a parenthesized list. Cases + where there is an absence of any parameters or where the URL is sent + unenclosed cause the command to behave precisely as specified in + [URLAUTH]. + + Similarly, if the URL is invalid, the command will behave precisely + as specified in [URLAUTH] and return a simple NIL. + + Available parameters are: + + BODYPARTSTRUCTURE + Provide a BODYPARTSTRUCTURE. + + BODYPARTSTRUCTURE is defined in [CONVERT] and provides metadata + useful for processing applications, such as the type of data. + + BINARY + Provide the data without any Content-Transfer-Encoding. + + In particular, this means that the data MAY contain NUL octets and + not be formed from textual lines. Data containing NUL octets MUST + be transferred using the literal8 syntax defined in [BINARY]. + + BODY + Provide the data as-is. + + This will provide the same data as the unextended [URLAUTH] as a + metadata item. + + Metadata items MUST NOT appear more than once per URL requested, and + clients MUST NOT request both BINARY and BODY. + +3.2. Response Metadata + + In order to carry any requested metadata and provide additional + information to the consumer, the URLFETCH response is similarly + extended. + + Following the URL itself, servers will include a series of + parenthesized metadata elements. Defined metadata elements are as + follows: + + + + + + +Cridland Standards Track [Page 3] + +RFC 5524 URLFETCH Binary May 2009 + + + BODYPARTSTRUCTURE + The BODYPARTSTRUCTURE provides information about the data + contained in the response, as it has been returned. It will + reflect any conversions or decoding that have taken place. In + particular, this will show an identity encoding if BINARY is also + requested. + + BINARY + The BINARY item provides the content, without any content transfer + encoding applied. If this is not possible (for example, the + content transfer encoding is unknown to the server), then this MAY + contain NIL. Servers MUST understand all identity content + transfer encodings defined in [MIME], as well as the + transformation encodings "Base64" [BASE64] and "Quoted-Printable" + [MIME]. + + BODY + The BODY item provides the content as found in the message, with + any content transfer encoding still applied. Requesting only the + BODY will provide equivalent functionality to the unextended + [URLAUTH], however, using the extended syntax described herein. + + Note that unlike [CONVERT], BODYPARTSTRUCTURE is not appended with + the part specifier, as this is implicit in the URL. + +4. Example Exchanges + + A client requests the data with no content transfer encoding. + + C: A001 URLFETCH ("imap://joe@example.com/INBOX/;uid=20/; + section=1.2;urlauth=anonymous:internal: + 91354a473744909de610943775f92038" BINARY) + S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; + section=1.2;urlauth=anonymous:internal: + 91354a473744909de610943775f92038" (BINARY {28} + S: Si vis pacem, para bellum. + S: + S: ) + S: A001 OK URLFETCH completed + + Note that the data here does not contain a NUL octet; therefore, a + literal -- not literal8 -- syntax has been used. + + A client again requests data with no content transfer encoding, but + this time requests the body structure. + + + + + + +Cridland Standards Track [Page 4] + +RFC 5524 URLFETCH Binary May 2009 + + + C: A001 URLFETCH ("imap://joe@example.com/INBOX/;uid=20/; + section=1.3;urlauth=anonymous:internal: + ae354a473744909de610943775f92038" BINARY BODYPARTSTRUCTURE) + S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; + section=1.3;urlauth=anonymous:internal: + ae354a473744909de610943775f92038" (BODYPARTSTRUCTURE + ("IMAGE" "PNG" () NIL NIL "BINARY" 123)) (BINARY ~{123} + S: [123 octets of data, some of which is NUL]) + S: A001 OK URLFETCH completed + + A client requests only the body structure. + + C: A001 URLFETCH ("imap://joe@example.com/INBOX/;uid=20/; + section=1.3;urlauth=anonymous:internal: + ae354a473744909de610943775f92038" BODYPARTSTRUCTURE) + S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; + section=1.3;urlauth=anonymous:internal: + ae354a473744909de610943775f92038" (BODYPARTSTRUCTURE + ("IMAGE" "PNG" () NIL NIL "BASE64" 164)) + S: A001 OK URLFETCH completed + + A client requests the body structure and the original content. + + C: A001 URLFETCH ("imap://joe@example.com/INBOX/;uid=20/; + section=1.3;urlauth=anonymous:internal: + ae354a473744909de610943775f92038" BODYPARTSTRUCTURE BODY) + S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; + section=1.3;urlauth=anonymous:internal: + ae354a473744909de610943775f92038" (BODYPARTSTRUCTURE + ("IMAGE" "PNG" () NIL NIL "BASE64" 164)) (BODY {164} + S: [164 octets of base64 encoded data]) + S: A001 OK URLFETCH completed + + Some parts cannot be decoded, so the server will provide the + BODYPARTSTRUCTURE of the part as is and provide NIL for the binary + content: + + C: A001 URLFETCH ("imap://joe@example.com/INBOX/;uid=20/; + section=1.4;urlauth=anonymous:internal: + 87ecbd02095b815e699503fc20d869c8" BODYPARTSTRUCTURE BINARY) + S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; + section=1.4;urlauth=anonymous:internal: + 87ecbd02095b815e699503fc20d869c8" (BODYPARTSTRUCTURE + ("IMAGE" "PNG" () NIL NIL "X-BLURDYBLOOP" 123)) + (BINARY NIL) + S: A001 OK URLFETCH completed + + + + + +Cridland Standards Track [Page 5] + +RFC 5524 URLFETCH Binary May 2009 + + + If a part simply doesn't exist, however, or the URI is invalid for + some other reason, then NIL is returned instead of metadata: + + C: A001 URLFETCH ("imap://joe@example.com/INBOX/;uid=20/; + section=200;urlauth=anonymous:internal: + 88066d37e2e5410e1a6486350a8836ee" BODYPARTSTRUCTURE BODY) + S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; + section=200;urlauth=anonymous:internal: + 88066d37e2e5410e1a6486350a8836ee" NIL + S: A001 OK URLFETCH completed + +5. Formal Syntax + + This formal syntax uses ABNF as specified in [ABNF], and includes + productions defined in [URLAUTH], [BINARY], and [IMAP]. + + capability =/ "URLAUTH=BINARY" + + ; Command parameters; see Section 3.1 + + urlfetch = "URLFETCH" 1*(SP url-fetch-arg) + + url-fetch-arg = url-fetch-simple / url-fetch-ext + + url-fetch-simple = url-full + ; Unextended URLFETCH. + + url-fetch-ext = "(" url-full *(SP url-fetch-param) ")" + ; If no url-fetch-param present, as unextended. + + url-fetch-param = "BODY" / "BINARY" / "BODYPARTSTRUCTURE" / atom + + ; Response; see Section 3.2 + + urlfetch-data = "*" SP "URLFETCH" + 1*(SP (urldata-simple / urldata-ext / + urldata-error)) + + urldata-error = SP url-full SP nil + + urldata-simple = SP url-full SP nstring + ; If client issues url-fetch-simple, server MUST respond with + ; urldata-simple. + + urldata-ext = SP url-full url-metadata + + url-metadata = 1*(SP "(" url-metadata-el ")") + + + + +Cridland Standards Track [Page 6] + +RFC 5524 URLFETCH Binary May 2009 + + + url-metadata-el = url-meta-bodystruct / url-meta-body / + url-meta-binary + + url-meta-bodystruct = "BODYPARTSTRUCTURE" SP body + + url-meta-binary = "BINARY" SP ( nstring / literal8 ) + ; If content contains a NUL octet, literal8 MUST be used. + ; Otherwise, content SHOULD use nstring. + ; On decoding error, NIL should be used. + + url-meta-body = "BODY" SP nstring + +6. IANA Considerations + + IMAP4 capabilities are registered by publishing a Standards Track or + IESG-approved Experimental RFC. + + This document defines the URLFETCH=BINARY IMAP capability. IANA has + added it to the registry accordingly. + +7. Security Considerations + + Implementors are directed to the security considerations within + [IMAP], [URLAUTH], and [BINARY]. + + The ability of the holder of a URL to be able to fetch metadata about + the content pointed to by the URL as well as the content itself + allows a potential attacker to discover more about the content than + was previously possible, including its original filename and user- + supplied description. + + The additional value of this information to an attacker is marginal, + and applies only to those URLs for which the attacker does not have + direct access, such as those produced by [URLAUTH]. Implementors are + therefore directed to the security considerations present in + [URLAUTH]. + +8. Acknowledgements + + Comments were received on this idea and/or document from Neil Cook, + Philip Guenther, Alexey Melnikov, Ken Murchison, and others. Whether + in agreement or dissent, the comments have refined and otherwise + influenced this document. + + + + + + + + +Cridland Standards Track [Page 7] + +RFC 5524 URLFETCH Binary May 2009 + + +9. References + +9.1. Normative References + + [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", STD 68, RFC 5234, January 2008. + + [BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data + Encodings", RFC 4648, October 2006. + + [BINARY] Nerenberg, L., "IMAP4 Binary Content Extension", + RFC 3516, April 2003. + + [CONVERT] Melnikov, A. and P. Coates, "Internet Message Access + Protocol - CONVERT Extension", RFC 5259, July 2008. + + [IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail + Extensions (MIME) Part One: Format of Internet Message + Bodies", RFC 2045, November 1996. + + [URLAUTH] Crispin, M., "Internet Message Access Protocol (IMAP) - + URLAUTH Extension", RFC 4467, May 2006. + +9.2. Informative References + + [BURL] Newman, C., "Message Submission BURL Extension", + RFC 4468, May 2006. + + [MEDIATYPE] Freed, N. and N. Borenstein, "Multipurpose Internet Mail + Extensions (MIME) Part Two: Media Types", RFC 2046, + November 1996. + + [STREAMING] Cook, N., "Streaming Internet Messaging Attachments", + Work in Progress, March 2009. + + + + + + + + + + + +Cridland Standards Track [Page 8] + +RFC 5524 URLFETCH Binary May 2009 + + +Author's Address + + Dave Cridland + Isode Limited + 5 Castle Business Village + 36, Station Road + Hampton, Middlesex TW12 2BX + GB + + EMail: dave.cridland@isode.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Cridland Standards Track [Page 9] + diff --git a/imap/docs/rfc/rfc5530.txt b/imap/docs/rfc/rfc5530.txt new file mode 100644 index 00000000..946fbb5f --- /dev/null +++ b/imap/docs/rfc/rfc5530.txt @@ -0,0 +1,507 @@ + + + + + + +Network Working Group A. Gulbrandsen +Request for Comments: 5530 Oryx Mail Systems GmbH +Category: Standards Track May 2009 + + + IMAP Response Codes + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (c) 2009 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents in effect on the date of + publication of this document (http://trustee.ietf.org/license-info). + Please review these documents carefully, as they describe your rights + and restrictions with respect to this document. + +Abstract + + IMAP responses consist of a response type (OK, NO, BAD), an optional + machine-readable response code, and a human-readable text. + + This document collects and documents a variety of machine-readable + response codes, for better interoperation and error reporting. + + + + + + + + + + + + + + + + + + +Gulbrandsen Standards Track [Page 1] + +RFC 5530 IMAP Response Codes May 2009 + + +1. Introduction + + Section 7.1 of [RFC3501] defines a number of response codes that can + help tell an IMAP client why a command failed. However, experience + has shown that more codes are useful. For example, it is useful for + a client to know that an authentication attempt failed because of a + server problem as opposed to a password problem. + + Currently, many IMAP servers use English-language, human-readable + text to describe these errors, and a few IMAP clients attempt to + translate this text into the user's language. + + This document names a variety of errors as response codes. It is + based on errors that have been checked and reported on in some IMAP + server implementations, and on the needs of some IMAP clients. + + This document doesn't require any servers to test for these errors or + any clients to test for these names. It only names errors for better + reporting and handling. + +2. Conventions Used in This Document + + Formal syntax is defined by [RFC5234] as modified by [RFC3501]. + + Example lines prefaced by "C:" are sent by the client and ones + prefaced by "S:" by the server. "[...]" means elision. + +3. Response Codes + + This section defines all the new response codes. Each definition is + followed by one or more examples. + + UNAVAILABLE + Temporary failure because a subsystem is down. For example, an + IMAP server that uses a Lightweight Directory Access Protocol + (LDAP) or Radius server for authentication might use this + response code when the LDAP/Radius server is down. + + C: a LOGIN "fred" "foo" + S: a NO [UNAVAILABLE] User's backend down for maintenance + + AUTHENTICATIONFAILED + Authentication failed for some reason on which the server is + unwilling to elaborate. Typically, this includes "unknown + user" and "bad password". + + + + + + +Gulbrandsen Standards Track [Page 2] + +RFC 5530 IMAP Response Codes May 2009 + + + This is the same as not sending any response code, except that + when a client sees AUTHENTICATIONFAILED, it knows that the + problem wasn't, e.g., UNAVAILABLE, so there's no point in + trying the same login/password again later. + + C: b LOGIN "fred" "foo" + S: b NO [AUTHENTICATIONFAILED] Authentication failed + + AUTHORIZATIONFAILED + Authentication succeeded in using the authentication identity, + but the server cannot or will not allow the authentication + identity to act as the requested authorization identity. This + is only applicable when the authentication and authorization + identities are different. + + C: c1 AUTHENTICATE PLAIN + [...] + S: c1 NO [AUTHORIZATIONFAILED] No such authorization-ID + + C: c2 AUTHENTICATE PLAIN + [...] + S: c2 NO [AUTHORIZATIONFAILED] Authenticator is not an admin + + + EXPIRED + Either authentication succeeded or the server no longer had the + necessary data; either way, access is no longer permitted using + that passphrase. The client or user should get a new + passphrase. + + C: d login "fred" "foo" + S: d NO [EXPIRED] That password isn't valid any more + + PRIVACYREQUIRED + The operation is not permitted due to a lack of privacy. If + Transport Layer Security (TLS) is not in use, the client could + try STARTTLS (see Section 6.2.1 of [RFC3501]) and then repeat + the operation. + + C: d login "fred" "foo" + S: d NO [PRIVACYREQUIRED] Connection offers no privacy + + C: d select inbox + S: d NO [PRIVACYREQUIRED] Connection offers no privacy + + + + + + + +Gulbrandsen Standards Track [Page 3] + +RFC 5530 IMAP Response Codes May 2009 + + + CONTACTADMIN + The user should contact the system administrator or support + desk. + + C: e login "fred" "foo" + S: e OK [CONTACTADMIN] + + NOPERM + The access control system (e.g., Access Control List (ACL), see + [RFC4314]) does not permit this user to carry out an operation, + such as selecting or creating a mailbox. + + C: f select "/archive/projects/experiment-iv" + S: f NO [NOPERM] Access denied + + INUSE + An operation has not been carried out because it involves + sawing off a branch someone else is sitting on. Someone else + may be holding an exclusive lock needed for this operation, or + the operation may involve deleting a resource someone else is + using, typically a mailbox. + + The operation may succeed if the client tries again later. + + C: g delete "/archive/projects/experiment-iv" + S: g NO [INUSE] Mailbox in use + + EXPUNGEISSUED + Someone else has issued an EXPUNGE for the same mailbox. The + client may want to issue NOOP soon. [RFC2180] discusses this + subject in depth. + + C: h search from fred@example.com + S: * SEARCH 1 2 3 5 8 13 21 42 + S: h OK [EXPUNGEISSUED] Search completed + + CORRUPTION + The server discovered that some relevant data (e.g., the + mailbox) are corrupt. This response code does not include any + information about what's corrupt, but the server can write that + to its logfiles. + + C: i select "/archive/projects/experiment-iv" + S: i NO [CORRUPTION] Cannot open mailbox + + + + + + + +Gulbrandsen Standards Track [Page 4] + +RFC 5530 IMAP Response Codes May 2009 + + + SERVERBUG + The server encountered a bug in itself or violated one of its + own invariants. + + C: j select "/archive/projects/experiment-iv" + S: j NO [SERVERBUG] This should not happen + + CLIENTBUG + The server has detected a client bug. This can accompany all + of OK, NO, and BAD, depending on what the client bug is. + + C: k1 select "/archive/projects/experiment-iv" + [...] + S: k1 OK [READ-ONLY] Done + C: k2 status "/archive/projects/experiment-iv" (messages) + [...] + S: k2 OK [CLIENTBUG] Done + + CANNOT + The operation violates some invariant of the server and can + never succeed. + + C: l create "///////" + S: l NO [CANNOT] Adjacent slashes are not supported + + LIMIT + The operation ran up against an implementation limit of some + kind, such as the number of flags on a single message or the + number of flags used in a mailbox. + + C: m STORE 42 FLAGS f1 f2 f3 f4 f5 ... f250 + S: m NO [LIMIT] At most 32 flags in one mailbox supported + + OVERQUOTA + The user would be over quota after the operation. (The user + may or may not be over quota already.) + + Note that if the server sends OVERQUOTA but doesn't support the + IMAP QUOTA extension defined by [RFC2087], then there is a + quota, but the client cannot find out what the quota is. + + C: n1 uid copy 1:* oldmail + S: n1 NO [OVERQUOTA] Sorry + + C: n2 uid copy 1:* oldmail + S: n2 OK [OVERQUOTA] You are now over your soft quota + + + + + +Gulbrandsen Standards Track [Page 5] + +RFC 5530 IMAP Response Codes May 2009 + + + ALREADYEXISTS + The operation attempts to create something that already exists, + such as when the CREATE or RENAME directories attempt to create + a mailbox and there is already one of that name. + + C: o RENAME this that + S: o NO [ALREADYEXISTS] Mailbox "that" already exists + + NONEXISTENT + The operation attempts to delete something that does not exist. + Similar to ALREADYEXISTS. + + C: p RENAME this that + S: p NO [NONEXISTENT] No such mailbox + +4. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [RFC5234]. [RFC3501] defines + the non-terminal "resp-text-code". + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper or lowercase characters to define + token strings is for editorial clarity only. + + resp-text-code =/ "UNAVAILABLE" / "AUTHENTICATIONFAILED" / + "AUTHORIZATIONFAILED" / "EXPIRED" / + "PRIVACYREQUIRED" / "CONTACTADMIN" / "NOPERM" / + "INUSE" / "EXPUNGEISSUED" / "CORRUPTION" / + "SERVERBUG" / "CLIENTBUG" / "CANNOT" / + "LIMIT" / "OVERQUOTA" / "ALREADYEXISTS" / + "NONEXISTENT" + +5. Security Considerations + + Revealing information about a passphrase to unauthenticated IMAP + clients causes bad karma. + + Response codes are easier to parse than human-readable text. This + can amplify the consequences of an information leak. For example, + selecting a mailbox can fail because the mailbox doesn't exist, + because the user doesn't have the "l" right (right to know the + mailbox exists) or "r" right (right to read the mailbox). If the + server sent different responses in the first two cases in the past, + only malevolent clients would discover it. With response codes it's + possible, perhaps probable, that benevolent clients will forward the + + + + + +Gulbrandsen Standards Track [Page 6] + +RFC 5530 IMAP Response Codes May 2009 + + + leaked information to the user. Server authors are encouraged to be + particularly careful with the NOPERM and authentication-related + responses. + +6. IANA Considerations + + The IANA has created the IMAP Response Codes registry. The registry + has been populated with the following codes: + + NEWNAME RFC 2060 (obsolete) + REFERRAL RFC 2221 + ALERT RFC 3501 + BADCHARSET RFC 3501 + PARSE RFC 3501 + PERMANENTFLAGS RFC 3501 + READ-ONLY RFC 3501 + READ-WRITE RFC 3501 + TRYCREATE RFC 3501 + UIDNEXT RFC 3501 + UIDVALIDITY RFC 3501 + UNSEEN RFC 3501 + UNKNOWN-CTE RFC 3516 + UIDNOTSTICKY RFC 4315 + APPENDUID RFC 4315 + COPYUID RFC 4315 + URLMECH RFC 4467 + TOOBIG RFC 4469 + BADURL RFC 4469 + HIGHESTMODSEQ RFC 4551 + NOMODSEQ RFC 4551 + MODIFIED RFC 4551 + COMPRESSIONACTIVE RFC 4978 + CLOSED RFC 5162 + NOTSAVED RFC 5182 + BADCOMPARATOR RFC 5255 + ANNOTATE RFC 5257 + ANNOTATIONS RFC 5257 + TEMPFAIL RFC 5259 + MAXCONVERTMESSAGES RFC 5259 + MAXCONVERTPARTS RFC 5259 + NOUPDATE RFC 5267 + METADATA RFC 5464 + NOTIFICATIONOVERFLOW RFC 5465 + BADEVENT RFC 5465 + UNDEFINED-FILTER RFC 5466 + UNAVAILABLE RFC 5530 + AUTHENTICATIONFAILED RFC 5530 + AUTHORIZATIONFAILED RFC 5530 + + + +Gulbrandsen Standards Track [Page 7] + +RFC 5530 IMAP Response Codes May 2009 + + + EXPIRED RFC 5530 + PRIVACYREQUIRED RFC 5530 + CONTACTADMIN RFC 5530 + NOPERM RFC 5530 + INUSE RFC 5530 + EXPUNGEISSUED RFC 5530 + CORRUPTION RFC 5530 + SERVERBUG RFC 5530 + CLIENTBUG RFC 5530 + CANNOT RFC 5530 + LIMIT RFC 5530 + OVERQUOTA RFC 5530 + ALREADYEXISTS RFC 5530 + NONEXISTENT RFC 5530 + + The new registry can be extended by sending a registration request to + IANA. IANA will forward this request to a Designated Expert, + appointed by the responsible IESG Area Director, CCing it to the IMAP + Extensions mailing list at <ietf-imapext@imc.org> (or a successor + designated by the Area Director). After either allowing 30 days for + community input on the IMAP Extensions mailing list or a successful + IETF Last Call, the expert will determine the appropriateness of the + registration request and either approve or disapprove the request by + sending a notice of the decision to the requestor, CCing the IMAP + Extensions mailing list and IANA. A denial notice must be justified + by an explanation, and, in cases where it is possible, concrete + suggestions on how the request can be modified so as to become + acceptable should be provided. + + For each response code, the registry contains a list of relevant RFCs + that describe (or extend) the response code and an optional response + code status description, such as "obsolete" or "reserved to prevent + collision with deployed software". (Note that in the latter case, + the RFC number can be missing.) Presence of the response code status + description means that the corresponding response code is NOT + RECOMMENDED for widespread use. + + The intention is that any future allocation will be accompanied by a + published RFC (including direct submissions to the RFC Editor). But + in order to allow for the allocation of values prior to the RFC being + approved for publication, the Designated Expert can approve + allocations once it seems clear that an RFC will be published, for + example, before requesting IETF LC for the document. + + The Designated Expert can also approve registrations for response + codes used in deployed software when no RFC exists. Such + registrations must be marked as "reserved to prevent collision with + deployed software". + + + +Gulbrandsen Standards Track [Page 8] + +RFC 5530 IMAP Response Codes May 2009 + + + Response code registrations may not be deleted; response codes that + are no longer believed appropriate for use (for example, if there is + a problem with the syntax of said response code or if the + specification describing it was moved to Historic) should be marked + "obsolete" in the registry, clearly marking the lists published by + IANA. + +7. Acknowledgements + + Peter Coates, Mark Crispin, Philip Guenther, Alexey Melnikov, Ken + Murchison, Chris Newman, Timo Sirainen, Philip Van Hoof, Dale + Wiggins, and Sarah Wilkin helped with this document. + +8. References + +8.1. Normative References + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", STD 68, RFC 5234, January + 2008. + +9. Informative References + + [RFC2087] Myers, J., "IMAP4 QUOTA extension", RFC 2087, January + 1997. + + [RFC2180] Gahrns, M., "IMAP4 Multi-Accessed Mailbox Practice", RFC + 2180, July 1997. + + [RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL) Extension", + RFC 4314, December 2005. + +Author's Address + + Arnt Gulbrandsen + Oryx Mail Systems GmbH + Schweppermannstr. 8 + D-81671 Muenchen + Germany + + Fax: +49 89 4502 9758 + EMail: arnt@oryx.com + + + + + + +Gulbrandsen Standards Track [Page 9] + diff --git a/imap/docs/rfc/rfc5593.txt b/imap/docs/rfc/rfc5593.txt new file mode 100644 index 00000000..20158d4e --- /dev/null +++ b/imap/docs/rfc/rfc5593.txt @@ -0,0 +1,563 @@ + + + + + + +Network Working Group N. Cook +Request for Comments: 5593 Cloudmark +Updates: 5092 June 2009 +Category: Standards Track + + + Internet Message Access Protocol (IMAP) - + URL Access Identifier Extension + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (c) 2009 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents in effect on the date of + publication of this document (http://trustee.ietf.org/license-info). + Please review these documents carefully, as they describe your rights + and restrictions with respect to this document. + +Abstract + + The existing IMAP URL specification (RFC 5092) lists several <access> + identifiers and <access> identifier prefixes that can be used to + restrict access to URLAUTH-generated URLs. However, these + identifiers do not provide facilities for new services such as + streaming. This document proposes a set of new <access> identifiers + as well as an IANA mechanism to register new <access> identifiers for + future applications. + + This document updates RFC 5092. + + + + + + + + + + + + +Cook Standards Track [Page 1] + +RFC 5593 IMAP URL Access Identifier June 2009 + + +Table of Contents + + 1. Introduction ....................................................2 + 2. Conventions Used in This Document ...............................2 + 3. Additional Authorized Access Identifiers ........................3 + 3.1. Existing Access Identifiers ................................3 + 3.2. Requirement for Additional Access Identifiers ..............3 + 3.3. Additional Access Identifier Specification .................4 + 3.4. Defining an Access Identifier for Streaming ................5 + 4. Formal Syntax ...................................................5 + 5. Acknowledgements ................................................6 + 6. IANA Considerations .............................................6 + 6.1. Access Identifier Registration Template ....................7 + 6.2. Stream Application Registration ............................7 + 6.3. Submit Application Registration ............................8 + 6.4. User Application Registration ..............................8 + 6.5. Authuser Application Registration ..........................9 + 6.6. Anonymous Application Registration .........................9 + 7. Security Considerations .........................................9 + 8. References .....................................................10 + 8.1. Normative References ......................................10 + 8.2. Informative References ....................................10 + +1. Introduction + + The IMAP URL specification [RFC5092] provides a way to carry + authorization information in IMAP URLs. Several authorization + <access> identifiers are specified in the document that allow + URLAUTH-authorized URLs to be used only by anonymous users, + authenticated users, or message submission entities. However, there + is no mechanism defined to create new <access> identifiers, and + overloading the existing mechanisms has security as well as + administrative implications. + + This document describes a new <access> identifier, "stream", to be + used by message streaming entities (as described in [STREAMING]), and + defines an IANA registration template, which can be used to register + new <access> identifiers for future applications. IANA definitions + for the existing access identifiers and prefixes from RFC 5092 are + also defined in this document -- this document updates RFC 5092 and + should be taken as the master in the event of any differences or + discrepancies. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [RFC2119]. + + + +Cook Standards Track [Page 2] + +RFC 5593 IMAP URL Access Identifier June 2009 + + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. If a single "C:" or "S:" label applies to + multiple lines, then some of the line breaks between those lines are + for editorial clarity only and may not be part of the actual protocol + exchange. + +3. Additional Authorized Access Identifiers + +3.1. Existing Access Identifiers + + The IMAP URL specification [RFC5092] specifies the following + authorized <access> identifiers: + + o "authuser" - Indicates that use of this URL is limited to + authenticated IMAP sessions that are logged in as any non- + anonymous user. + + o "anonymous" - Indicates that use of this URL is not restricted by + session authorization identity. + + Additionally, the following <access> identifier prefixes are defined + in [RFC5092]: + + o "submit+" - Followed by a userid, indicates that only a userid + authorized as a message submission entity on behalf of the + specified userid is permitted to use this URL. + + o "user+" - Followed by a userid, indicates that use of this URL is + limited to IMAP sessions that are logged in as the specified + userid. + +3.2. Requirement for Additional Access Identifiers + + The existing <access> identifiers are suitable for user-based + authorization, but only the "submit+" <access> identifier prefix is + suitable for entities acting on behalf of a user. Generic support + for external entities acting on behalf of users is required for new + services such as streaming [STREAMING]. + + The "submit+" <access> identifier prefix is not suitable for use as a + general mechanism to grant access to entities acting on behalf of + users, for reasons that include: + + o Security - The IMAP server maintains a list of submission server + entities that are entitled to retrieve IMAP URLs specifying the + "submit+" <access> identifier prefix. If this list is extended to + include the set of all external entities that could act on behalf + of users, then the attack surface would be increased. + + + +Cook Standards Track [Page 3] + +RFC 5593 IMAP URL Access Identifier June 2009 + + + o Administration - When URLAUTH-style IMAP URLs are presented to an + IMAP server by entities acting on behalf of users, the server + administrator has no way of determining the intended use of that + URL from the server logs. + + o Resourcing - Without a mechanism to distinguish between the + application for which an IMAP URL is to be used, the IMAP server + has no way to prioritize resources for particular applications. + For example, the server could prioritize "submit+" URL fetch + requests over other access identifiers. + +3.3. Additional Access Identifier Specification + + The previous section establishes that additional access identifiers + are required to support applications, such as streaming [STREAMING], + that require entities to retrieve URLAUTH URLs on behalf of users. + This section describes the scope and meaning of any additional + <access> identifiers that are created. + + Additional <access> identifiers MUST take one of two forms (Section 4 + gives the formal ABNF syntax): + + o <access> identifier - The name of the application, e.g., + "exampleapp". + + o <access> identifier prefix - The name of the application, e.g., + "exampleapp3", followed by a "+" and then a userid. For example, + consider "exampleapp3+testuser". + + Note that an <access> identifier name can also be registered as an + <access> identifier prefix. However, this would require 2 separate + IANA registrations. + + In both cases, the semantics are the same as those for "submit+", + i.e., the <access> identifier or <access> identifier prefix (which + MUST be followed by a userid) indicates that only a userid authorized + as an application entity for the specified application is permitted + to use this URL. In the case of <access> identifier prefixes, the + IMAP server SHALL NOT validate the specified userid but MUST validate + that the IMAP session has an authorization identity that is + authorized as an application entity for the specified application. + + + + + + + + + + +Cook Standards Track [Page 4] + +RFC 5593 IMAP URL Access Identifier June 2009 + + + The application entity itself MAY choose to perform validation on any + specified userid before attempting to retrieve the URL. + + The authorization granted by any <access> identifiers used as + described above is self-describing, and so requires that the IMAP + server provide an extensible mechanism for associating userids with + new applications. For example, imagine a new application, "foo", is + created that requires application entities to retrieve URLs on behalf + of users. In this case, the IMAP server would need to provide a way + to register the new application "foo" and to associate the set of + userids to be used by those entities with the application "foo". Any + attempt to retrieve URLs containing the <access> identifier "foo" + would be checked for authorization against the list of userids + associated with the application "foo". + + Section 6 provides the template required to register new <access> + identifiers or prefixes with IANA. + +3.4. Defining an Access Identifier for Streaming + + One application that makes use of URLAUTH-authorized URLs is that of + streaming multimedia files that are received as internet-messaging + attachments. This application is described in [STREAMING]. + + See Section 6.2 for the IANA registration template for the "stream" + <access> identifier. + +4. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [RFC5234]. + + Except as noted otherwise, all alphabetic characters are case- + insensitive. The use of upper- or lower-case characters to define + token strings is for editorial clarity only. Implementations MUST + accept these strings in a case-insensitive fashion. + + The ABNF specified below updates the formal syntax of <access> + identifiers as defined in IMAP URL [RFC5092]. + + Copyright (c) 2009 IETF Trust and the persons identified as + authors of the code. All rights reserved. + + Redistribution and use in source and binary forms, with or without + modification, are permitted provided that the following conditions + are met: + + + + + +Cook Standards Track [Page 5] + +RFC 5593 IMAP URL Access Identifier June 2009 + + + - Redistributions of source code must retain the above copyright + notice, this list of conditions and the following disclaimer. + + - Redistributions in binary form must reproduce the above copyright + notice, this list of conditions and the following disclaimer in + the documentation and/or other materials provided with the + distribution. + + - Neither the name of Internet Society, IETF or IETF Trust, nor the + names of specific contributors, may be used to endorse or promote + products derived from this software without specific prior + written permission. + + THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR + A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT + OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT + LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, + DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY + THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT + (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE + OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + + application = 1*(ALPHA/DIGIT) + + access =/ application / (application "+" enc-user) + +5. Acknowledgements + + This document was inspired by discussions in the Lemonade Working + Group. + +6. IANA Considerations + + IANA created a new registry for IMAP URLAUTH access identifiers and + prefixes. + + Access identifiers and prefixes MUST be registered using the "IETF + Review" policy [RFC5226]. This section gives the IANA registration + entries for the existing access identifiers and prefixes from RFC + 5092 as well as the entry for the "stream" application. + + + + + + + + + +Cook Standards Track [Page 6] + +RFC 5593 IMAP URL Access Identifier June 2009 + + +6.1. Access Identifier Registration Template + + To: iana@iana.org + Subject: IMAP URL Access Identifier Registration + + Type: [Either "<access> identifier" or + "<access> identifier prefix"] + + Application: [Name of the application, e.g., "stream"] + + Description: [A description of the application and its use + of IMAP URLs] + + RFC Number: [Number of the RFC in which the application is + defined] + + Contact: [Email and/or physical address to contact for + additional information] + +6.2. Stream Application Registration + + To: iana@iana.org + Subject: IMAP URL Access Identifier Registration + + Type: <access> identifier + + Application: stream + + Description: Used by SIP Media Servers to retrieve + attachments for streaming to email + clients + + RFC Number: RFC 5593 + + Contact: Neil Cook <neil.cook@noware.co.uk> + + + + + + + + + + + + + + + + +Cook Standards Track [Page 7] + +RFC 5593 IMAP URL Access Identifier June 2009 + + +6.3. Submit Application Registration + + To: iana@iana.org + Subject: IMAP URL Access Identifier Registration + + Type: <access> identifier prefix + + Application: submit + + Description: Used by message submission entities to + retrieve attachments to be included in + submitted messages + + RFC Number: RFC 5593 and RFC 5092 + + Contact: Lemonade WG <lemonade@ietf.org> + +6.4. User Application Registration + + To: iana@iana.org + Subject: IMAP URL Access Identifier Registration + + Type: <access> identifier prefix + + Application: user + + Description: Used to restrict access to IMAP sessions + that are logged in as the specified userid + + RFC Number: RFC 5593 and RFC 5092 + + Contact: Lemonade WG <lemonade@ietf.org> + + + + + + + + + + + + + + + + + + + +Cook Standards Track [Page 8] + +RFC 5593 IMAP URL Access Identifier June 2009 + + +6.5. Authuser Application Registration + + To: iana@iana.org + Subject: IMAP URL Access Identifier Registration + + Type: <access> identifier + + Application: authuser + + Description: Used to restrict access to IMAP sessions + that are logged in as any non-anonymous + user of that IMAP server + + RFC Number: RFC 5593 and RFC 5092 + + Contact: Lemonade WG <lemonade@ietf.org> + +6.6. Anonymous Application Registration + + To: iana@iana.org + Subject: IMAP URL Access Identifier Registration + + Type: <access> identifier + + Application: anonymous + + Description: Indicates that use of this URL is + not restricted by session authorization + identity + + RFC Number: RFC 5593 and RFC 5092 + + Contact: Lemonade WG <lemonade@ietf.org> + +7. Security Considerations + + The extension to <access> identifiers specified in this document + provides a mechanism for extending the semantics of the "submit+" + <access> prefix to arbitrary applications. The use of such + additional <access> identifiers and prefixes is primarily for + security purposes, i.e., to prevent the overloading of "submit+" as a + generic mechanism to allow entities to retrieve IMAP URLs on behalf + of userids. Other than this, the security implications are identical + to those discussed in Section 10.1 of IMAPURL [RFC5092]. + + + + + + + +Cook Standards Track [Page 9] + +RFC 5593 IMAP URL Access Identifier June 2009 + + +8. References + +8.1. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC5092] Melnikov, A., Ed., and C. Newman, "IMAP URL Scheme", RFC + 5092, November 2007. + + [RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", STD 68, RFC 5234, January + 2008. + +8.2. Informative References + + [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an + IANA Considerations Section in RFCs", BCP 26, RFC 5226, + May 2008. + + [STREAMING] Cook, N., "Streaming Internet Messaging Attachments", + Work in Progress, May 2009. + +Author's Address + + Neil L Cook + Cloudmark + + EMail: neil.cook@noware.co.uk + + + + + + + + + + + + + + + + + + + + + + +Cook Standards Track [Page 10] + diff --git a/imap/docs/rfc/rfc5738.txt b/imap/docs/rfc/rfc5738.txt new file mode 100644 index 00000000..2b5daaa2 --- /dev/null +++ b/imap/docs/rfc/rfc5738.txt @@ -0,0 +1,843 @@ + + + + + + +Network Working Group P. Resnick +Request for Comments: 5738 Qualcomm Incorporated +Updates: 3501 C. Newman +Category: Experimental Sun Microsystems + March 2010 + + + IMAP Support for UTF-8 + +Abstract + + This specification extends the Internet Message Access Protocol + version 4rev1 (IMAP4rev1) to support UTF-8 encoded international + characters in user names, mail addresses, and message headers. + +Status of This Memo + + This document is not an Internet Standards Track specification; it is + published for examination, experimental implementation, and + evaluation. + + This document defines an Experimental Protocol for the Internet + community. This document is a product of the Internet Engineering + Task Force (IETF). It represents the consensus of the IETF + community. It has received public review and has been approved for + publication by the Internet Engineering Steering Group (IESG). Not + all documents approved by the IESG are a candidate for any level of + Internet Standard; see Section 2 of RFC 5741. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + http://www.rfc-editor.org/info/rfc5738. + +Copyright Notice + + Copyright (c) 2010 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents + (http://trustee.ietf.org/license-info) in effect on the date of + publication of this document. Please review these documents + carefully, as they describe your rights and restrictions with respect + to this document. Code Components extracted from this document must + include Simplified BSD License text as described in Section 4.e of + the Trust Legal Provisions and are provided without warranty as + described in the Simplified BSD License. + + + + +Resnick & Newman Experimental [Page 1] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + + This document may contain material from IETF Documents or IETF + Contributions published or made publicly available before November + 10, 2008. The person(s) controlling the copyright in some of this + material may not have granted the IETF Trust the right to allow + modifications of such material outside the IETF Standards Process. + Without obtaining an adequate license from the person(s) controlling + the copyright in such materials, this document may not be modified + outside the IETF Standards Process, and derivative works of it may + not be created outside the IETF Standards Process, except to format + it for publication as an RFC or to translate it into languages other + than English. + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 + 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 + 3. UTF8=ACCEPT IMAP Capability . . . . . . . . . . . . . . . . . 3 + 3.1. IMAP UTF-8 Quoted Strings . . . . . . . . . . . . . . . . 3 + 3.2. UTF8 Parameter to SELECT and EXAMINE . . . . . . . . . . . 5 + 3.3. UTF-8 LIST and LSUB Responses . . . . . . . . . . . . . . 5 + 3.4. UTF-8 Interaction with IMAP4 LIST Command Extensions . . . 6 + 3.4.1. UTF8 and UTF8ONLY LIST Selection Options . . . . . . . 6 + 3.4.2. UTF8 LIST Return Option . . . . . . . . . . . . . . . 6 + 4. UTF8=APPEND Capability . . . . . . . . . . . . . . . . . . . . 7 + 5. UTF8=USER Capability . . . . . . . . . . . . . . . . . . . . . 7 + 6. UTF8=ALL Capability . . . . . . . . . . . . . . . . . . . . . 7 + 7. UTF8=ONLY Capability . . . . . . . . . . . . . . . . . . . . . 8 + 8. Up-Conversion Server Requirements . . . . . . . . . . . . . . 8 + 9. Issues with UTF-8 Header Mailstore . . . . . . . . . . . . . . 9 + 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 + 11. Security Considerations . . . . . . . . . . . . . . . . . . . 11 + 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 + 12.1. Normative References . . . . . . . . . . . . . . . . . . . 11 + 12.2. Informative References . . . . . . . . . . . . . . . . . . 13 + Appendix A. Design Rationale . . . . . . . . . . . . . . . . . . 14 + Appendix B. Examples Demonstrating Relationships between + UTF8= Capabilities . . . . . . . . . . . . . . . . . 15 + Appendix C. Acknowledgments . . . . . . . . . . . . . . . . . . . 15 + + + + + + + + + + + + + +Resnick & Newman Experimental [Page 2] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + +1. Introduction + + This specification extends IMAP4rev1 [RFC3501] to permit UTF-8 + [RFC3629] in headers as described in "Internationalized Email + Headers" [RFC5335]. It also adds a mechanism to support mailbox + names, login names, and passwords using the UTF-8 charset. This + specification creates five new IMAP capabilities to allow servers to + advertise these new extensions, along with two new IMAP LIST + selection options and a new IMAP LIST return option. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" + in this document are to be interpreted as defined in "Key words for + use in RFCs to Indicate Requirement Levels" [RFC2119]. + + The formal syntax uses the Augmented Backus-Naur Form (ABNF) + [RFC5234] notation including the core rules defined in Appendix B of + [RFC5234]. In addition, rules from IMAP4rev1 [RFC3501], UTF-8 + [RFC3629], "Collected Extensions to IMAP4 ABNF" [RFC4466], and IMAP4 + LIST Command Extensions [RFC5258] are also referenced. + + In examples, "C:" and "S:" indicate lines sent by the client and + server, respectively. If a single "C:" or "S:" label applies to + multiple lines, then the line breaks between those lines are for + editorial clarity only and are not part of the actual protocol + exchange. + +3. UTF8=ACCEPT IMAP Capability + + The "UTF8=ACCEPT" capability indicates that the server supports UTF-8 + quoted strings, the "UTF8" parameter to SELECT and EXAMINE, and UTF-8 + responses from the LIST and LSUB commands. + + A client MUST use the "ENABLE UTF8=ACCEPT" command (defined in + [RFC5161]) to indicate to the server that the client accepts UTF-8 + quoted-strings. The "ENABLE UTF8=ACCEPT" command MUST only be used + in the authenticated state. (Note that the "UTF8=ONLY" capability + described in Section 7 and the "UTF8=ALL" capability described in + Section 6 imply the "UTF8=ACCEPT" capability. See additional + information in these sections.) + +3.1. IMAP UTF-8 Quoted Strings + + The IMAP4rev1 [RFC3501] base specification forbids the use of 8-bit + characters in atoms or quoted strings. Thus, a UTF-8 string can only + be sent as a literal. This can be inconvenient from a coding + standpoint, and unless the server offers IMAP4 non-synchronizing + + + +Resnick & Newman Experimental [Page 3] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + + literals [RFC2088], this requires an extra round trip for each UTF-8 + string sent by the client. When the IMAP server advertises the + "UTF8=ACCEPT" capability, it informs the client that it supports + native UTF-8 quoted-strings with the following syntax: + + string =/ utf8-quoted + + utf8-quoted = "*" DQUOTE *UQUOTED-CHAR DQUOTE + + UQUOTED-CHAR = QUOTED-CHAR / UTF8-2 / UTF8-3 / UTF8-4 + ; UTF8-2, UTF8-3, and UTF8-4 are as defined in RFC 3629 + + When this quoting mechanism is used by the client (specifically an + octet sequence beginning with *" and ending with "), then the server + MUST reject octet sequences with the high bit set that fail to comply + with the formal syntax in [RFC3629] with a BAD response. + + The IMAP server MUST NOT send utf8-quoted syntax to the client unless + the client has indicated support for that syntax by using the "ENABLE + UTF8=ACCEPT" command. + + If the server advertises the "UTF8=ACCEPT" capability, the client MAY + use utf8-quoted syntax with any IMAP argument that permits a string + (including astring and nstring). However, if characters outside the + US-ASCII repertoire are used in an inappropriate place, the results + would be the same as if other syntactically valid but semantically + invalid characters were used. For example, if the client includes + UTF-8 characters in the user or password arguments (and the server + has not advertised "UTF8=USER"), the LOGIN command will fail as it + would with any other invalid user name or password. Specific cases + where UTF-8 characters are permitted or not permitted are described + in the following paragraphs. + + All IMAP servers that advertise the "UTF8=ACCEPT" capability SHOULD + accept UTF-8 in mailbox names, and those that also support the + "Mailbox International Naming Convention" described in RFC 3501, + Section 5.1.3 MUST accept utf8-quoted mailbox names and convert them + to the appropriate internal format. Mailbox names MUST comply with + the Net-Unicode Definition (Section 2 of [RFC5198]) with the specific + exception that they MUST NOT contain control characters (0000-001F, + 0080-009F), delete (007F), line separator (2028), or paragraph + separator (2029). + + An IMAP client MUST NOT issue a SEARCH command that uses a mixture of + utf8-quoted syntax and a SEARCH CHARSET other than UTF-8. If an IMAP + server receives such a SEARCH command, it SHOULD reject the command + with a BAD response (due to the conflicting charset labels). + + + + +Resnick & Newman Experimental [Page 4] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + +3.2. UTF8 Parameter to SELECT and EXAMINE + + The "UTF8=ACCEPT" capability also indicates that the server supports + the "UTF8" parameter to SELECT and EXAMINE. When a mailbox is + selected with the "UTF8" parameter, it alters the behavior of all + IMAP commands related to message sizes, message headers, and MIME + body headers so they refer to the message with UTF-8 headers. If the + mailstore is not UTF-8 header native and the SELECT or EXAMINE + command with UTF-8 header modifier succeeds, then the server MUST + return results as if the mailstore were UTF-8 header native with + upconversion requirements as described in Section 8. The server MAY + reject the SELECT or EXAMINE command with the [NOT-UTF-8] response + code, unless the "UTF8=ALL" or "UTF8=ONLY" capability is advertised. + + Servers MAY include mailboxes that can only be selected or examined + if the "UTF8" parameter is provided. However, such mailboxes MUST + NOT be included in the output of an unextended LIST, LSUB, or + equivalent command. If a client attempts to SELECT or EXAMINE such + mailboxes without the "UTF8" parameter, the server MUST reject the + command with a [UTF-8-ONLY] response code. As a result, such + mailboxes will not be accessible by IMAP clients written prior to + this specification and are discouraged unless the server advertises + "UTF8=ONLY" or the server implements IMAP4 LIST Command Extensions + [RFC5258]. + + utf8-select-param = "UTF8" + ;; Conforms to <select-param> from RFC 4466 + + C: a SELECT newmailbox (UTF8) + S: ... + S: a OK SELECT completed + C: b FETCH 1 (SIZE ENVELOPE BODY) + S: ... < UTF-8 header native results > + S: b OK FETCH completed + + C: c EXAMINE legacymailbox (UTF8) + S: c NO [NOT-UTF-8] Mailbox does not support UTF-8 access + + C: d SELECT funky-new-mailbox + S: d NO [UTF-8-ONLY] Mailbox requires UTF-8 client + +3.3. UTF-8 LIST and LSUB Responses + + After an IMAP client successfully issues an "ENABLE UTF8=ACCEPT" + command, the server MUST NOT return in LIST results any mailbox names + to the client following the IMAP4 Mailbox International Naming + Convention. Instead, the server MUST return any mailbox names with + characters outside the US-ASCII repertoire using utf8-quoted syntax. + + + +Resnick & Newman Experimental [Page 5] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + + (The IMAP4 Mailbox International Naming Convention has proved + problematic in the past, so the desire is to make this syntax + obsolete as quickly as possible.) + +3.4. UTF-8 Interaction with IMAP4 LIST Command Extensions + + When an IMAP server advertises both the "UTF8=ACCEPT" capability and + the "LIST-EXTENDED" [RFC5258] capability, the server MUST support the + LIST extensions described in this section. + +3.4.1. UTF8 and UTF8ONLY LIST Selection Options + + The "UTF8" LIST selection option tells the server to include + mailboxes that only support UTF-8 headers in the output of the list + command. The "UTF8ONLY" LIST selection option tells the server to + include all mailboxes that support UTF-8 headers and to exclude + mailboxes that don't support UTF-8 headers. Note that "UTF8ONLY" + implies "UTF8", so it is not necessary for the client to request + both. Use of either selection option will also result in UTF-8 + mailbox names in the result as described in Section 3.3 and implies + the "UTF8" List return option described in Section 3.4.2. + +3.4.2. UTF8 LIST Return Option + + If the client supplies the "UTF8" LIST return option, then the server + MUST include either the "\NoUTF8" or the "\UTF8Only" mailbox + attribute as appropriate. The "\NoUTF8" mailbox attribute indicates + that an attempt to SELECT or EXAMINE that mailbox with the "UTF8" + parameter will fail with a [NOT-UTF-8] response code. The + "\UTF8Only" mailbox attribute indicates that an attempt to SELECT or + EXAMINE that mailbox without the "UTF8" parameter will fail with a + [UTF-8-ONLY] response code. Note that computing this information may + be expensive on some server implementations, so this return option + should not be used unless necessary. + + The ABNF [RFC5234] for these LIST extensions follows: + + list-select-independent-opt =/ "UTF8" + + list-select-base-opt =/ "UTF8ONLY" + + mbx-list-oflag =/ "\NoUTF8" / "\UTF8Only" + + return-option =/ "UTF8" + + resp-text-code =/ "NOT-UTF-8" / "UTF-8-ONLY" + + + + + +Resnick & Newman Experimental [Page 6] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + +4. UTF8=APPEND Capability + + If the "UTF8=APPEND" capability is advertised, then the server + accepts UTF-8 headers in the APPEND command message argument. A + client that sends a message with UTF-8 headers to the server MUST + send them using the "UTF8" APPEND data extension. If the server also + advertises the CATENATE capability (as specified in [RFC4469]), the + client can use the same data extension to include such a message in a + CATENATE message part. The ABNF for the APPEND data extension and + CATENATE extension follows: + + utf8-literal = "UTF8" SP "(" literal8 ")" + + append-data =/ utf8-literal + + cat-part =/ utf8-literal + + A server that advertises "UTF8=APPEND" has to comply with the + requirements of the IMAP base specification and [RFC5322] for message + fetching. Mechanisms for 7-bit downgrading to help comply with the + standards are discussed in Downgrading mechanism for + Internationalized eMail Address (IMA) [RFC5504]. + + IMAP servers that do not advertise the "UTF8=APPEND" or "UTF8=ONLY" + capability SHOULD reject an APPEND command that includes any 8-bit in + the message headers with a "NO" response. + + Note that the "UTF8=ONLY" capability described in Section 7 implies + the "UTF8=APPEND" capability. See additional information in that + section. + +5. UTF8=USER Capability + + If the "UTF8=USER" capability is advertised, that indicates the + server accepts UTF-8 user names and passwords and applies SASLprep + [RFC4013] to both arguments of the LOGIN command. The server MUST + reject UTF-8 that fails to comply with the formal syntax in RFC 3629 + [RFC3629] or if it encounters Unicode characters listed in Section + 2.3 of SASLprep RFC 4013 [RFC4013]. + +6. UTF8=ALL Capability + + The "UTF8=ALL" capability indicates all server mailboxes support + UTF-8 headers. Specifically, SELECT and EXAMINE with the "UTF8" + parameter will never fail with a [NOT-UTF-8] response code. + + + + + + +Resnick & Newman Experimental [Page 7] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + + Note that the "UTF8=ONLY" capability described in Section 7 implies + the "UTF8=ALL" capability. See additional information in that + section. + + Note that the "UTF8=ALL" capability implies the "UTF8=ACCEPT" + capability. + +7. UTF8=ONLY Capability + + The "UTF8=ONLY" capability permits an IMAP server to advertise that + it does not support the international mailbox name convention + (modified UTF-7), and does not permit selection or examination of any + mailbox unless the "UTF8" parameter is provided. As this is an + incompatible change to IMAP, a clear warning is necessary. IMAP + clients that find implementation of the "UTF8=ONLY" capability + problematic are encouraged to at least detect the "UTF8=ONLY" + capability and provide an informative error message to the end-user. + + When an IMAP mailbox internally uses UTF-8 header native storage, the + down-conversion step is necessary to permit selection or examination + of the mailbox in a backwards compatible fashion will become more + difficult to support. Although it is hoped that deployed IMAP + servers will not advertise "UTF8=ONLY" for some years, this + capability is intended to minimize the disruption when legacy support + finally goes away. + + The "UTF8=ONLY" capability implies the "UTF8=ACCEPT" capability, the + "UTF8=ALL" capability, and the "UTF8=APPEND" capability. A server + that advertises "UTF8=ONLY" need not advertise the three implicit + capabilities. + +8. Up-Conversion Server Requirements + + When an IMAP4 server uses a traditional mailbox format that includes + 7-bit headers and it chooses to permit access to that mailbox with + the "UTF8" parameter, it MUST support minimal up-conversion as + described in this section. + + The server MUST support up-conversion of the following address + header-fields in the message header: From, Sender, To, CC, Bcc, + Resent-From, Resent-Sender, Resent-To, Resent-CC, Resent-Bcc, and + Reply-To. This up-conversion MUST include address local-parts in + fields downgraded according to [RFC5504], address domains encoded + according to Internationalizing Domain Names in Applications (IDNA) + [RFC3490], and MIME header encoding [RFC2047] of display-names and + any [RFC5322] comments. + + + + + +Resnick & Newman Experimental [Page 8] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + + The following charsets MUST be supported for up-conversion of MIME + header encoding [RFC2047]: UTF-8, US-ASCII, ISO-8859-1, ISO-8859-2, + ISO-8859-3, ISO-8859-4, ISO-8859-5, ISO-8859-6, ISO-8859-7, + ISO-8859-8, ISO-8859-9, ISO-8859-10, ISO-8859-14, and ISO-8859-15. + If the server supports other charsets in IMAP SEARCH or IMAP CONVERT + [RFC5259], it SHOULD also support those charsets in this conversion. + + Up-conversion of MIME header encoding of the following headers MUST + also be implemented: Subject, Date ([RFC5322] comments only), + Comments, Keywords, and Content-Description. + + Server implementations also SHOULD up-convert all MIME body headers + [RFC2045], SHOULD up-convert or remove the deprecated (and misused) + "name" parameter [RFC1341] on Content-Type, and MUST up-convert the + Content-Disposition [RFC2183] "filename" parameter, except when any + of these are contained within a multipart/signed MIME body part (see + below). These parameters can be encoded using the standard MIME + parameter encoding [RFC2231] mechanism, or via non-standard use of + MIME header encoding [RFC2047] in quoted strings. + + The IMAP server MUST NOT perform up-conversion of headers and content + of multipart/signed, as well as Original-Recipient and Return-Path. + +9. Issues with UTF-8 Header Mailstore + + When an IMAP server uses a mailbox format that supports UTF-8 headers + and it permits selection or examination of that mailbox without the + "UTF8" parameter, it is the responsibility of the server to comply + with the IMAP4rev1 base specification [RFC3501] and [RFC5322] with + respect to all header information transmitted over the wire. + Mechanisms for 7-bit downgrading to help comply with the standards + are discussed in "Downgrading Mechanism for Email Address + Internationalization" [RFC5504]. + + An IMAP server with a mailbox that supports UTF-8 headers MUST comply + with the protocol requirements implicit from Section 8. However, the + code necessary for such compliance need not be part of the IMAP + server itself in this case. For example, the minimal required up- + conversion could be performed when a message is inserted into the + IMAP-accessible mailbox. + +10. IANA Considerations + + This adds five new capabilities ("UTF8=ACCEPT", "UTF8=USER", + "UTF8=APPEND", "UTF8=ALL", and "UTF8=ONLY") to the IMAP4rev1 + Capabilities registry [RFC3501]. + + + + + +Resnick & Newman Experimental [Page 9] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + + This adds two new IMAP4 list selection options and one new IMAP4 list + return option. + + 1. LIST-EXTENDED option name: UTF8 + + LIST-EXTENDED option type: SELECTION + + Implied return options(s): UTF8 + + LIST-EXTENDED option description: Causes the LIST response to + include mailboxes that mandate the UTF8 SELECT/EXAMINE parameter. + + Published specification: RFC 5738, Section 3.4.1 + + Security considerations: RFC 5738, Section 11 + + Intended usage: COMMON + + Person and email address to contact for further information: see + the Authors' Addresses at the end of this specification + + Owner/Change controller: iesg@ietf.org + + 2. LIST-EXTENDED option name: UTF8ONLY + + LIST-EXTENDED option type: SELECTION + + Implied return options(s): UTF8 + + LIST-EXTENDED option description: Causes the LIST response to + include mailboxes that mandate the UTF8 SELECT/EXAMINE parameter + and exclude mailboxes that do not support the UTF8 SELECT/EXAMINE + parameter. + + Published specification: RFC 5738, Section 3.4.1 + + Security considerations: RFC 5738, Section 11 + + Intended usage: COMMON + + Person and email address to contact for further information: see + the Authors' Addresses at the end of this specification + + Owner/Change controller: iesg@ietf.org + + + + + + + +Resnick & Newman Experimental [Page 10] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + + 3. LIST-EXTENDED option name: UTF8 + + LIST-EXTENDED option type: RETURN + + Implied return options(s): none + + LIST-EXTENDED option description: Causes the LIST response to + include \NoUTF8 and \UTF8Only mailbox attributes. + + Published specification: RFC 5738, Section 3.4.1 + + Security considerations: RFC 5738, Section 11 + + Intended usage: COMMON + + Person and email address to contact for further information: see + the Authors' Addresses at the end of this specification + + Owner/Change controller: iesg@ietf.org + +11. Security Considerations + + The security considerations of UTF-8 [RFC3629] and SASLprep [RFC4013] + apply to this specification, particularly with respect to use of + UTF-8 in user names and passwords. Otherwise, this is not believed + to alter the security considerations of IMAP4rev1. + +12. References + +12.1. Normative References + + [RFC1341] Borenstein, N. and N. Freed, "MIME (Multipurpose Internet + Mail Extensions): Mechanisms for Specifying and Describing + the Format of Internet Message Bodies", RFC 1341, + June 1992. + + [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail + Extensions (MIME) Part One: Format of Internet Message + Bodies", RFC 2045, November 1996. + + [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) + Part Three: Message Header Extensions for Non-ASCII Text", + RFC 2047, November 1996. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + + + + +Resnick & Newman Experimental [Page 11] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + + [RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating + Presentation Information in Internet Messages: The + Content-Disposition Header Field", RFC 2183, August 1997. + + [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded + Word Extensions: + Character Sets, Languages, and Continuations", RFC 2231, + November 1997. + + [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, + "Internationalizing Domain Names in Applications (IDNA)", + RFC 3490, March 2003. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO + 10646", STD 63, RFC 3629, November 2003. + + [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names + and Passwords", RFC 4013, February 2005. + + [RFC4466] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4 + ABNF", RFC 4466, April 2006. + + [RFC4469] Resnick, P., "Internet Message Access Protocol (IMAP) + CATENATE Extension", RFC 4469, April 2006. + + [RFC5161] Gulbrandsen, A. and A. Melnikov, "The IMAP ENABLE + Extension", RFC 5161, March 2008. + + [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network + Interchange", RFC 5198, March 2008. + + [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", STD 68, RFC 5234, January 2008. + + [RFC5258] Leiba, B. and A. Melnikov, "Internet Message Access + Protocol version 4 - LIST Command Extensions", RFC 5258, + June 2008. + + [RFC5259] Melnikov, A. and P. Coates, "Internet Message Access + Protocol - CONVERT Extension", RFC 5259, July 2008. + + [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, + October 2008. + + + + + +Resnick & Newman Experimental [Page 12] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + + [RFC5335] Abel, Y., "Internationalized Email Headers", RFC 5335, + September 2008. + + [RFC5504] Fujiwara, K. and Y. Yoneya, "Downgrading Mechanism for + Email Address Internationalization", RFC 5504, March 2009. + +12.2. Informative References + + [RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet Mail + Extensions (MIME) Part Five: Conformance Criteria and + Examples", RFC 2049, November 1996. + + [RFC2088] Myers, J., "IMAP4 non-synchronizing literals", RFC 2088, + January 1997. + + [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and + Languages", BCP 18, RFC 2277, January 1998. + + [RFC5721] Gellens, R. and C. Newman, "POP3 Support for UTF-8", + RFC 5721, February 2010. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Resnick & Newman Experimental [Page 13] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + +Appendix A. Design Rationale + + This non-normative section discusses the reasons behind some of the + design choices in the above specification. + + The basic approach of advertising the ability to access a mailbox in + UTF-8 mode is intended to permit graceful upgrade, including servers + that support multiple mailbox formats. In particular, it would be + undesirable to force conversion of an entire server mailstore to + UTF-8 headers, so being able to phase-in support for new mailboxes + and gradually migrate old mailboxes is permitted by this design. + + "UTF8=USER" is optional because many identity systems are US-ASCII + only, so it's helpful to inform the client up front that UTF-8 won't + work. + + "UTF8=APPEND" is optional because it effectively requires IMAP server + support for down-conversion, which is a much more complex operation + than up-conversion. + + The "UTF8=ONLY" mechanism simplifies diagnosis of interoperability + problems when legacy support goes away. In the situation where + backwards compatibility is broken anyway, just-send-UTF-8 IMAP has + the advantage that it might work with some legacy clients. However, + the difficulty of diagnosing interoperability problems caused by a + just-send-UTF-8 IMAP mechanism is the reason the "UTF8=ONLY" + capability mechanism was chosen. + + The up-conversion requirements are designed to balance the desire to + deprecate and eventually eliminate complicated encodings (like MIME + header encodings) without creating a significant deployment burden + for servers. As IMAP4 servers already require a MIME parser, this + includes additional server up-conversion requirements not present in + POP3 Support for UTF-8 [RFC5721]. + + The set of mandatory charsets comes from two sources: MIME + requirements [RFC2049] and IETF Policy on Character Sets [RFC2277]. + Including a requirement to up-convert widely deployed encoded + ideographic charsets to UTF-8 would be reasonable for most scenarios, + but may require unacceptable table sizes for some embedded devices. + The open-ended recommendation to support widely deployed charsets + avoids the political ramifications of attempting to list such + charsets. The authors believe market forces, existing open-source + software, and public conversion tables are sufficient to deploy the + appropriate charsets. + + + + + + +Resnick & Newman Experimental [Page 14] + +RFC 5738 IMAP Support for UTF-8 March 2010 + + +Appendix B. Examples Demonstrating Relationships between UTF8= + Capabilities + + + UTF8=ACCEPT UTF8=USER UTF8=APPEND + UTF8=ACCEPT UTF8=ALL + UTF8=ALL ; Note, same as above + UTF8=ACCEPT UTF8=USER UTF8=APPEND UTF8=ALL UTF8=ONLY + UTF8=USER UTF8=ONLY ; Note, same as above + +Appendix C. Acknowledgments + + The authors wish to thank the participants of the EAI working group + for their contributions to this document with particular thanks to + Harald Alvestrand, David Black, Randall Gellens, Arnt Gulbrandsen, + Kari Hurtta, John Klensin, Xiaodong Lee, Charles Lindsey, Alexey + Melnikov, Subramanian Moonesamy, Shawn Steele, Daniel Taharlev, and + Joseph Yee for their specific contributions to the discussion. + +Authors' Addresses + + Pete Resnick + Qualcomm Incorporated + 5775 Morehouse Drive + San Diego, CA 92121-1714 + US + + Phone: +1 858 651 4478 + EMail: presnick@qualcomm.com + URI: http://www.qualcomm.com/~presnick/ + + Chris Newman + Sun Microsystems + 800 Royal Oaks + Monrovia, CA 91016 + US + + EMail: chris.newman@sun.com + + + + + + + + + + + + + +Resnick & Newman Experimental [Page 15] + diff --git a/imap/docs/rfc/rfc5788.txt b/imap/docs/rfc/rfc5788.txt new file mode 100644 index 00000000..fe0de709 --- /dev/null +++ b/imap/docs/rfc/rfc5788.txt @@ -0,0 +1,619 @@ + + + + + + +Internet Engineering Task Force (IETF) A. Melnikov +Request for Comments: 5788 D. Cridland +Category: Standards Track Isode Limited +ISSN: 2070-1721 March 2010 + + + IMAP4 Keyword Registry + +Abstract + + The aim of this document is to establish a new IANA registry for IMAP + keywords and to define a procedure for keyword registration, in order + to improve interoperability between different IMAP clients. + +Status of This Memo + + This is an Internet Standards Track document. + + This document is a product of the Internet Engineering Task Force + (IETF). It represents the consensus of the IETF community. It has + received public review and has been approved for publication by the + Internet Engineering Steering Group (IESG). Further information on + Internet Standards is available in Section 2 of RFC 5741. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + http://www.rfc-editor.org/info/rfc5788. + +Copyright Notice + + Copyright (c) 2010 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents + (http://trustee.ietf.org/license-info) in effect on the date of + publication of this document. Please review these documents + carefully, as they describe your rights and restrictions with respect + to this document. Code Components extracted from this document must + include Simplified BSD License text as described in Section 4.e of + the Trust Legal Provisions and are provided without warranty as + described in the Simplified BSD License. + + + + + + + + + +Melnikov & Cridland Standards Track [Page 1] + +RFC 5788 IMAP4 Keyword Registry March 2010 + + +Table of Contents + + 1. Introduction ....................................................2 + 2. Conventions Used in This Document ...............................2 + 3. IANA Considerations .............................................3 + 3.1. Review Guidelines for the Designated Expert Reviewer .......4 + 3.2. Comments on IMAP Keywords' Registrations ...................5 + 3.3. Change Control .............................................5 + 3.4. Initial Registrations ......................................6 + 3.4.1. $MDNSent IMAP Keyword Registration ..................6 + 3.4.2. $Forwarded IMAP Keyword Registration ................7 + 3.4.3. $SubmitPending IMAP Keyword Registration ............8 + 3.4.4. $Submitted IMAP Keyword Registration ................9 + 4. Security Considerations ........................................10 + 5. Acknowledgements ...............................................10 + 6. References .....................................................10 + 6.1. Normative References ......................................10 + 6.2. Informative References ....................................11 + +1. Introduction + + IMAP keywords [RFC3501] are boolean named flags that can be used by + clients to annotate messages in an IMAP mailbox. Although IMAP + keywords are an optional feature of IMAP, the majority of IMAP + servers can store arbitrary keywords. Many mainstream IMAP clients + use a limited set of specific keywords, and some can manage (create, + edit, display) arbitrary IMAP keywords. + + Over the years, some IMAP keywords have become de-facto standards, + with some specific semantics associated with them. In some cases, + different client implementors decided to define and use keywords with + different names, but the same semantics. Some server implementors + decided to map such keywords automatically in order to improve cross- + client interoperability. + + In other cases, the same keywords have been used with different + semantics, thus causing interoperability problems. + + This document attempts to prevent further incompatible uses of IMAP + keywords by establishing an "IMAP Keywords" registry and allocating a + special prefix for standardized keywords. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [Kwds]. + + + + +Melnikov & Cridland Standards Track [Page 2] + +RFC 5788 IMAP4 Keyword Registry March 2010 + + +3. IANA Considerations + + IANA has established a new registry for IMAP keywords. + + Registration of an IMAP keyword is requested by filling in the + following template and following the instructions on the IANA pages + for the registry to submit it to IANA: + + Subject: Registration of IMAP keyword X + + IMAP keyword name: + + Purpose (description): + + Private or Shared on a server: (One of PRIVATE, SHARED, or BOTH. + PRIVATE means that each different + user has a distinct copy of the + keyword. SHARED means that all + different users see the same value of + the keyword. BOTH means that an IMAP + server can have the keyword as either + private or shared.) + + Is it an advisory keyword or may it cause an automatic action: + + When/by whom the keyword is set/cleared: + + Related keywords: (for example, "mutually exclusive with keywords Y + and Z") + + Related IMAP capabilities: + + Security considerations: + + Published specification (recommended): + + Person & email address to contact for further information: + + Intended usage: (One of COMMON, LIMITED USE, or DEPRECATED (i.e., + not recommended for use)) + + Owner/Change controller: (MUST be "IESG" for any "common use" + keyword registration specified in an IETF + Review document. See definition of "common + use" below in this section. When the + Owner/Change controller is not a + Standardization Organization, the + registration request MUST make it clear if + + + +Melnikov & Cridland Standards Track [Page 3] + +RFC 5788 IMAP4 Keyword Registry March 2010 + + + the registration is controlled by a + company, or the individual performing the + registration.) + + Note: (Any other information that the author deems interesting + may be added here, for example, if the keyword(s) is + supported by existing clients.) + + Registration of an IMAP keyword requires Expert Review [RFC5226]. + Registration of any IMAP keyword is initiated by posting a + registration request to the Message Organization WG mailing list + <morg@ietf.org> (or its replacement as chosen by the responsible + Application Area Director) and CCing IANA (<iana@iana.org>). After + allowing for at least two weeks for community input on the designated + mailing list, the expert will determine the appropriateness of the + registration request and either approve or disapprove the request + with notice to the requestor, the mailing list, and IANA. Any + refusal must come with a clear explanation. + + The IESG appoints one or more Expert Reviewers for the IMAP keyword + registry established by this document. + + The Expert Reviewer should strive for timely reviews. The Expert + Reviewer should take no longer than six weeks to make and announce + the decision, or notify the mailing list that more time is required. + + Decisions (or lack of) made by an Expert Reviewer can be first + appealed to Application Area Directors and, if the appellant is not + satisfied with the response, to the full IESG. + + There are two types of IMAP keywords in the "IMAP Keywords" registry: + intended for "common use" and vendor-/organization-specific use (also + known as "limited use"). An IMAP keyword is said to be for "common + use" if it is reasonably expected to be implemented in at least two + independent client implementations. The two types of IMAP keywords + have different levels of requirements for registration (see below). + +3.1. Review Guidelines for the Designated Expert Reviewer + + Expert Reviewers should focus on the following requirements. + + Registration of a vendor-/organization-specific ("limited use") IMAP + keyword is easier. The Expert Reviewer only needs to check that the + requested name doesn't conflict with an already registered name, and + that the name is not too generic, misleading, etc. The Expert + Reviewer MAY request the IMAP keyword name change before approving + + + + + +Melnikov & Cridland Standards Track [Page 4] + +RFC 5788 IMAP4 Keyword Registry March 2010 + + + the registration. The Expert Reviewer SHOULD refuse a registration + if there is an already registered IMAP keyword that serves the same + purpose, but has a different name. + + When registering an IMAP keyword for "common use", the Expert + Reviewer performs the checks described for vendor-/ + organization-specific IMAP keywords, plus additional checks as + detailed below. + + Keywords intended for "common use" SHOULD start with the "$" prefix. + (Note that this is a SHOULD because some of the commonly used IMAP + keywords in widespread use don't follow this convention.) + + IMAP keywords intended for "common use" SHOULD be standardized in + IETF Review [RFC5226] documents. (Note that IETF Review documents + still require Expert Review.) + + Values in the "IMAP Keywords" IANA registry intended for "common use" + must be clearly documented and likely to ensure interoperability. + They must be useful, not harmful to the Internet. In cases when an + IMAP keyword being registered is already deployed, Expert Reviewers + should favor registering it over requiring perfect documentation + and/or requesting a change to the name of the IMAP keyword. + + The Expert Reviewer MAY automatically "upgrade" registration requests + for a "limited use" IMAP keyword to "common use" level. The Expert + Reviewer MAY also request that a registration targeted for "common + use" be registered as "limited use" instead. + +3.2. Comments on IMAP Keywords' Registrations + + Comments on registered IMAP keywords should be sent to both the + "owner" of the mechanism and to the mailing list designated to IMAP + keyword review (see Section 3). This improves the chances of getting + a timely response. + + Submitters of comments may, after a reasonable attempt to contact the + owner and after soliciting comments on the IMAP mailing list, request + the designated Expert Reviewer to attach their comment to the IMAP + keyword registration itself. The procedure is similar to requesting + an Expert Review for the affected keyword. + +3.3. Change Control + + Once an IMAP keyword registration has been published by IANA, the + owner may request a change to its definition. The change request + (including a change to the "intended usage" field) follows the same + procedure as the initial registration request, with the exception of + + + +Melnikov & Cridland Standards Track [Page 5] + +RFC 5788 IMAP4 Keyword Registry March 2010 + + + changes to the "Person & email address to contact for further + information" and "Owner/Change controller" fields. The latter can be + changed by the owner by informing IANA; this can be done without + discussion or review. + + The IESG may reassign responsibility for an IMAP keyword. The most + common case of this will be to enable clarifications to be made to + keywords where the owner of the registration has died, moved out of + contact, or is otherwise unable to make changes that are important to + the community. + + IMAP keyword registrations MUST NOT be deleted; keywords that are no + longer believed appropriate for use can be declared DEPRECATED by a + change to their "intended usage" field. + + The IESG is considered the owner of all "common use" IMAP keywords + that are published in an IETF Review document. + +3.4. Initial Registrations + + IANA has registered the IMAP keywords specified in following + subsections in the registry established by this document. + +3.4.1. $MDNSent IMAP Keyword Registration + + Subject: Registration of IMAP keyword $MDNSent + + + IMAP keyword name: $MDNSent + + Purpose (description): Specifies that a Message Disposition + Notification (MDN) must not be sent for any + message annotated with the $MDNSent IMAP + keyword. + + Private or Shared on a server: SHARED + + Is it an advisory keyword or may it cause an automatic action: + This keyword can cause automatic action by + the client. See [RFC3503] for more details. + + When/by whom the keyword is set/cleared: + This keyword is set by an IMAP client when it + decides to act on an MDN request, or when + uploading a sent or draft message. It can + also be set by a delivery agent. Once set, + the flag SHOULD NOT be cleared. + + + + +Melnikov & Cridland Standards Track [Page 6] + +RFC 5788 IMAP4 Keyword Registry March 2010 + + + Related keywords: None + + Related IMAP capabilities: None + + Security considerations: See Section 6 of [RFC3503] + + Published specification (recommended): [RFC3503] + + Person & email address to contact for further information: + Alexey Melnikov <alexey.melnikov@isode.com> + + Intended usage: COMMON + + Owner/Change controller: IESG + + Note: + +3.4.2. $Forwarded IMAP Keyword Registration + + Subject: Registration of the IMAP keyword $Forwarded + + IMAP keyword name: $Forwarded + + Purpose (description): $Forwarded is used by several IMAP clients to + specify that the message was resent to + another email address, embedded within or + attached to a new message. This keyword is + set by the mail client when it successfully + forwards the message to another email + address. Typical usage of this keyword is to + show a different (or additional) icon for a + message that has been forwarded. + + Private or Shared on a server: BOTH + + Is it an advisory keyword or may it cause an automatic action: + advisory + + When/by whom the keyword is set/cleared: + This keyword can be set by either a delivery + agent or a mail client. Once set, the flag + SHOULD NOT be cleared. Notes: There is no + way to tell if a message with $Forwarded + keyword set was forwarded more than once. + + Related keywords: None + + Related IMAP capabilities: None + + + +Melnikov & Cridland Standards Track [Page 7] + +RFC 5788 IMAP4 Keyword Registry March 2010 + + + Security considerations: A server implementing this keyword as a + shared keyword may disclose that a + confidential message was forwarded. + + Published specification (recommended): [RFC5550] + + Person & email address to contact for further information: + Alexey Melnikov <alexey.melnikov@isode.com> + + Intended usage: COMMON + + Owner/Change controller: IESG + + Note: + +3.4.3. $SubmitPending IMAP Keyword Registration + + Subject: Registration of IMAP keyword $SubmitPending + + IMAP keyword name: $SubmitPending + + Purpose (description): The $SubmitPending IMAP keyword designates + the message as awaiting to be submitted. + This keyword allows storing messages waiting + to be submitted in the same mailbox where + messages that were already submitted and/or + are being edited are stored. + + A message that has both $Submitted and + $SubmitPending IMAP keywords set is a message + being actively submitted. + + Private or Shared on a server: SHARED + + Is it an advisory keyword or may it cause an automatic action: + This keyword can cause automatic action by + the client. See Section 5.10 of [RFC5550] + for more details. + + When/by whom the keyword is set/cleared: + This keyword is set by a mail client when it + decides that the message needs to be sent + out. + + Related keywords: $Submitted + + Related IMAP capabilities: None + + + + +Melnikov & Cridland Standards Track [Page 8] + +RFC 5788 IMAP4 Keyword Registry March 2010 + + + Security considerations: A server implementing this keyword as a + shared keyword may disclose that a + confidential message is scheduled to be + sent out or is being actively sent out. + + Published specification (recommended): [RFC5550] + + Person & email address to contact for further information: + Alexey Melnikov <alexey.melnikov@isode.com> + + Intended usage: COMMON + + Owner/Change controller: IESG + + Note: + +3.4.4. $Submitted IMAP Keyword Registration + + Subject: Registration of IMAP keyword $Submitted + + IMAP keyword name: $Submitted + + Purpose (description): The $Submitted IMAP keyword designates the + message as being sent out. + + A message that has both $Submitted and + $SubmitPending IMAP keywords set is a message + being actively submitted. + + Private or Shared on a server: SHARED + + Is it an advisory keyword or may it cause an automatic action: + This keyword can cause automatic action by + the client. See Section 5.10 of [RFC5550] + for more details. + + When/by whom the keyword is set/cleared: + This keyword is set by a mail client when it + decides to start sending it. + + Related keywords: $SubmitPending + + Related IMAP capabilities: None + + Security considerations: A server implementing this keyword as a + shared keyword may disclose that a + confidential message was sent or is being + actively sent out. + + + +Melnikov & Cridland Standards Track [Page 9] + +RFC 5788 IMAP4 Keyword Registry March 2010 + + + Published specification (recommended): [RFC5550] + + Person & email address to contact for further information: + Alexey Melnikov <alexey.melnikov@isode.com> + + Intended usage: COMMON + + Owner/Change controller: IESG + + Note: + +4. Security Considerations + + IMAP keywords are one of the base IMAP features [RFC3501]. This + document doesn't change their behavior, so it does not add new + security issues. + + A particular IMAP keyword might have specific security + considerations, which are documented in the IMAP keyword + registration template standardized by this document. + +5. Acknowledgements + + The creation of this document was prompted by one of many discussions + on the IMAP mailing list. + + John Neystadt co-authored the first version of this document. + + Special thanks to Chris Newman, David Harris, Lyndon Nerenberg, Mark + Crispin, Samuel Weiler, Alfred Hoenes, Lars Eggert, and Cullen + Jennings for reviewing different versions of this document. However, + all errors or omissions must be attributed to the authors of this + document. + + The authors would also like to thank the developers of Mozilla mail + clients for providing food for thought. + +6. References + +6.1. Normative References + + [Kwds] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + + + + +Melnikov & Cridland Standards Track [Page 10] + +RFC 5788 IMAP4 Keyword Registry March 2010 + + + [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an + IANA Considerations Section in RFCs", BCP 26, RFC 5226, + May 2008. + +6.2. Informative References + + [RFC3503] Melnikov, A., "Message Disposition Notification (MDN) + profile for Internet Message Access Protocol (IMAP)", + RFC 3503, March 2003. + + [RFC5550] Cridland, D., Melnikov, A., and S. Maes, "The Internet + Email to Support Diverse Service Environments (Lemonade) + Profile", RFC 5550, August 2009. + +Authors' Addresses + + Alexey Melnikov + Isode Limited + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: Alexey.Melnikov@isode.com + URI: http://www.melnikov.ca/ + + + Dave Cridland + Isode Limited + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: dave.cridland@isode.com + + + + + + + + + + + + + + + + +Melnikov & Cridland Standards Track [Page 11] + diff --git a/imap/docs/rfc/rfc5819.txt b/imap/docs/rfc/rfc5819.txt new file mode 100644 index 00000000..e45b8558 --- /dev/null +++ b/imap/docs/rfc/rfc5819.txt @@ -0,0 +1,339 @@ + + + + + + +Internet Engineering Task Force (IETF) A. Melnikov +Request for Comments: 5819 Isode Limited +Category: Standards Track T. Sirainen +ISSN: 2070-1721 Unaffiliated + March 2010 + + + IMAP4 Extension for Returning STATUS Information in Extended LIST + +Abstract + + Many IMAP clients display information about total number of + messages / total number of unseen messages in IMAP mailboxes. In + order to do that, they are forced to issue a LIST or LSUB command and + to list all available mailboxes, followed by a STATUS command for + each mailbox found. This document provides an extension to LIST + command that allows the client to request STATUS information for + mailboxes together with other information typically returned by the + LIST command. + +Status of This Memo + + This is an Internet Standards Track document. + + This document is a product of the Internet Engineering Task Force + (IETF). It represents the consensus of the IETF community. It has + received public review and has been approved for publication by the + Internet Engineering Steering Group (IESG). Further information on + Internet Standards is available in Section 2 of RFC 5741. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + http://www.rfc-editor.org/info/rfc5819. + +Copyright Notice + + Copyright (c) 2010 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents + (http://trustee.ietf.org/license-info) in effect on the date of + publication of this document. Please review these documents + carefully, as they describe your rights and restrictions with respect + to this document. Code Components extracted from this document must + include Simplified BSD License text as described in Section 4.e of + the Trust Legal Provisions and are provided without warranty as + described in the Simplified BSD License. + + + +Melnikov & Sirainen Standards Track [Page 1] + +RFC 5819 TITLE* March 2010 + + +Table of Contents + + 1. Introduction ....................................................2 + 1.1. Conventions Used in This Document ..........................2 + 2. STATUS Return Option to LIST Command ............................2 + 3. Examples ........................................................3 + 4. Formal Syntax ...................................................4 + 5. Security Considerations .........................................4 + 6. IANA Considerations .............................................4 + 7. Acknowledgements ................................................5 + 8. Normative References ............................................5 + +1. Introduction + + Many IMAP clients display information about the total number of + messages / total number of unseen messages in IMAP mailboxes. In + order to do that, they are forced to issue a LIST or LSUB command and + to list all available mailboxes, followed by a STATUS command for + each mailbox found. This document provides an extension to LIST + command that allows the client to request STATUS information for + mailboxes together with other information typically returned by the + LIST command. + +1.1. Conventions Used in This Document + + In examples, "C:" indicates lines sent by a client that is connected + to a server. "S:" indicates lines sent by the server to the client. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [Kwds]. + +2. STATUS Return Option to LIST Command + + [RFC3501] explicitly disallows mailbox patterns in the STATUS + command. The main reason was to discourage frequent use of the + STATUS command by clients, as it might be quite expensive for an IMAP + server to perform. However, this prohibition had resulted in an + opposite effect: a new generation of IMAP clients appeared, that + issues a STATUS command for each mailbox returned by the LIST + command. This behavior is suboptimal to say at least. It wastes + extra bandwidth and, in the case of a client that doesn't support + IMAP pipelining, also degrades performance by using too many round + trips. This document tries to remedy the situation by specifying a + single command that can be used by the client to request all the + necessary information. In order to achieve this goal, this document + is extending the LIST command with a new return option, STATUS. This + option takes STATUS data items as parameters. For each selectable + + + +Melnikov & Sirainen Standards Track [Page 2] + +RFC 5819 TITLE* March 2010 + + + mailbox matching the list pattern and selection options, the server + MUST return an untagged LIST response followed by an untagged STATUS + response containing the information requested in the STATUS return + option. + + If an attempted STATUS for a listed mailbox fails because the mailbox + can't be selected (e.g., if the "l" ACL right [ACL] is granted to the + mailbox and the "r" right is not granted, or due to a race condition + between LIST and STATUS changing the mailbox to \NoSelect), the + STATUS response MUST NOT be returned and the LIST response MUST + include the \NoSelect attribute. This means the server may have to + buffer the LIST reply until it has successfully looked up the + necessary STATUS information. + + If the server runs into unexpected problems while trying to look up + the STATUS information, it MAY drop the corresponding STATUS reply. + In such a situation, the LIST command would still return a tagged OK + reply. + +3. Examples + + C: A01 LIST "" % RETURN (STATUS (MESSAGES UNSEEN)) + S: * LIST () "." "INBOX" + S: * STATUS "INBOX" (MESSAGES 17 UNSEEN 16) + S: * LIST () "." "foo" + S: * STATUS "foo" (MESSAGES 30 UNSEEN 29) + S: * LIST (\NoSelect) "." "bar" + S: A01 OK List completed. + + The "bar" mailbox isn't selectable, so it has no STATUS reply. + + C: A02 LIST (SUBSCRIBED RECURSIVEMATCH)"" % RETURN (STATUS + (MESSAGES)) + S: * LIST (\Subscribed) "." "INBOX" + S: * STATUS "INBOX" (MESSAGES 17) + S: * LIST () "." "foo" (CHILDINFO ("SUBSCRIBED")) + S: A02 OK List completed. + + The LIST reply for "foo" is returned because it has matching + children, but no STATUS reply is returned because "foo" itself + doesn't match the selection criteria. + + + + + + + + + + +Melnikov & Sirainen Standards Track [Page 3] + +RFC 5819 TITLE* March 2010 + + +4. Formal Syntax + + The following syntax specification uses the augmented Backus-Naur + Form (BNF) as described in [ABNF]. Terms not defined here are taken + from [RFC3501] and [LISTEXT]. + + return-option =/ status-option + + status-option = "STATUS" SP "(" status-att *(SP status-att) ")" + ;; This ABNF production complies with + ;; <option-extension> syntax. + +5. Security Considerations + + This extension makes it a bit easier for clients to overload the + server by requesting STATUS information for a large number of + mailboxes. However, as already noted in the introduction, existing + clients already try to do that by generating a large number of STATUS + commands for each mailbox in which they are interested. While + performing STATUS information retrieval for big lists of mailboxes, a + server implementation needs to make sure that it can still serve + other IMAP connections and yield execution to other connections, when + necessary. + +6. IANA Considerations + + IMAP4 capabilities are registered by publishing a Standards Track or + IESG-approved Experimental RFC. The "IMAP 4 Capabilities" registry + is available from the IANA webiste: + + http://www.iana.org + + This document defines the LIST-STATUS IMAP capability. IANA has + added it to the registry. + + IANA has also added the following new LIST-EXTENDED option to the + IANA registry established by [LISTEXT]: + + To: iana@iana.org + Subject: Registration of LIST-EXTENDED option STATUS + + LIST-EXTENDED option name: STATUS + + LIST-EXTENDED option type: RETURN + + LIST-EXTENDED option description: Causes the LIST command to return + STATUS responses in addition to LIST responses. + + + + +Melnikov & Sirainen Standards Track [Page 4] + +RFC 5819 TITLE* March 2010 + + + Published specification: RFC 5819 + + Security considerations: RFC 5819 + + Intended usage: COMMON + + Person and email address to contact for further information: + Alexey Melnikov <Alexey.Melnikov@isode.com> + + Owner/Change controller: iesg@ietf.org + +7. Acknowledgements + + Thanks to Philip Van Hoof who pointed out that STATUS and LIST + commands should be combined in order to optimize traffic and number + of round trips. + +8. Normative References + + [ABNF] Crocker, D., Ed., and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", STD 68, RFC 5234, January + 2008. + + [ACL] Melnikov, A., "IMAP4 Access Control List (ACL) Extension", + RFC 4314, December 2005. + + [Kwds] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [LISTEXT] Leiba, B. and A. Melnikov, "Internet Message Access + Protocol version 4 - LIST Command Extensions", RFC 5258, + June 2008. + + [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION + 4rev1", RFC 3501, March 2003. + + + + + + + + + + + + + + + + +Melnikov & Sirainen Standards Track [Page 5] + +RFC 5819 TITLE* March 2010 + + +Authors' Addresses + + Alexey Melnikov + Isode Limited + 5 Castle Business Village + 36 Station Road + Hampton, Middlesex TW12 2BX + UK + + EMail: Alexey.Melnikov@isode.com + URI: http://www.melnikov.ca/ + + + Timo Sirainen + + EMail: tss@iki.fi + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Melnikov & Sirainen Standards Track [Page 6] + |