Internet Message Access Protocol (IMAP) - MULTIAPPEND Extension
RFC 3502

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Network Working Group                                         M. Crispin
Request for Comments: 3502                      University of Washington
Category: Standards Track                                     March 2003

    Internet Message Access Protocol (IMAP) - MULTIAPPEND Extension

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document describes the multiappending extension to the Internet
   Message Access Protocol (IMAP) (RFC 3501).  This extension provides
   substantial performance improvements for IMAP clients which upload
   multiple messages at a time to a mailbox on the server.

   A server which supports this extension indicates this with a
   capability name of "MULTIAPPEND".

Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "MAY", and "OPTIONAL" in this document are to
   be interpreted as described in [KEYWORDS].

Introduction

   The MULTIAPPEND extension permits uploading of multiple messages with
   a single command.  When used in conjunction with the [LITERAL+]
   extension, the entire upload is accomplished in a single
   command/response round trip.

   A MULTIAPPEND APPEND operation is atomic; either all messages are
   successfully appended, or no messages are appended.

   In the base IMAP specification, each message must be appended in a
   separate command, and there is no mechanism to "unappend" messages if
   an error occurs while appending.  Also, some mail stores may require

Crispin                     Standards Track                     [Page 1]
RFC 3502                    IMAP MULTIAPPEND                  March 2003

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

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

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

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

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

6.3.11.  APPEND Command

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

   Data:       no specific responses for this command

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

Crispin                     Standards Track                     [Page 2]
RFC 3502                    IMAP MULTIAPPEND                  March 2003

      The APPEND command appends the literal arguments as new messages
      to the end of the specified destination mailbox.  This argument
      SHOULD be in the format of an [RFC-2822] message.  8-bit
      characters are permitted in the message.  A server implementation
      that is unable to preserve 8-bit data properly MUST be able to
      reversibly convert 8-bit APPEND data to 7-bit using a [MIME-IMB]
      content transfer encoding.

            Note: There MAY be exceptions, e.g., draft messages, in
            which required [RFC-2822] header lines are omitted in the