rfc4551.txt

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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



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      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]



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      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



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   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




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      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)



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      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:





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         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