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+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).
+
+
+
+
+
+
+
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+
+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
+
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+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".
+
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+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
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+Acknowledgement
+
+   Funding for the RFC Editor function is provided by the IETF
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+
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+
+
+
+
+Melnikov & Hole             Standards Track                    [Page 25]
+