From 7fe712882b909931088a318c08041b0e7974a000 Mon Sep 17 00:00:00 2001 From: Eduardo Chappa Date: Sat, 2 Nov 2013 02:51:18 -0600 Subject: * 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. --- imap/docs/rfc/rfc5255.txt | 1123 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 1123 insertions(+) create mode 100644 imap/docs/rfc/rfc5255.txt (limited to 'imap/docs/rfc/rfc5255.txt') 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= 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= 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] + -- cgit v1.2.3-54-g00ecf