RFC 3502 (rfc3502) - Page 2 of 7

Internet Message Access Protocol (IMAP) - MULTIAPPEND Extension

RFC 3502                    IMAP MULTIAPPEND                  March 2003


   an expensive "open/lock + sync/unlock/close" operation as part of
   appending; this can be quite expensive if it must be done on a
   per-message basis.

   If the server supports both LITERAL+ and pipelining but not
   MULTIAPPEND, it may be possible to get some of the performance
   advantages of MULTIAPPEND by doing a pipelined "batch" append.
   However, it will not work as well as MULTIAPPEND for the following
   reasons:

        1) Multiple APPEND commands, even as part of a pipelined batch,
        are non-atomic by definition.  There is no way to revert the
        mailbox to the state before the batch append in the event of an
        error.

        2) It may not be feasible for the server to coalesce pipelined
        APPEND operations so as to avoid the "open/lock +
        sync/unlock/close" overhead described above.  In any case, such
        coalescing would be timing dependent and thus potentially
        unreliable.  In particular, with traditional UNIX mailbox files,
        it is assumed that a lock is held only for a single atomic
        operation, and many applications disregard any lock that is
        older than 5 minutes.

        3) If an error occurs, depending upon the nature of the error,
        it is possible for additional messages to be appended after the
        error.  For example, the user wants to append 5 messages, but a
        disk quota error occurs with the third message because of its
        size.  However, the fourth and fifth messages have already been
        sent in the pipeline, so the mailbox ends up with the first,
        second, fourth, and fifth messages of the batch appended.

6.3.11.  APPEND Command

   Arguments:  mailbox name
               one or more messages to upload, specified as:
                  OPTIONAL flag parenthesized list
                  OPTIONAL date/time string
                  message literal

   Data:       no specific responses for this command

   Result:     OK - append completed
               NO - append error: can't append to that mailbox, error
                    in flags or date/time or message text,
                    append cancelled
               BAD - command unknown or arguments invalid




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