path: root/doc/rfc/rfc6851.txt

Internet Engineering Task Force (IETF)                    A. Gulbrandsen
Request for Comments: 6851
Category: Standards Track                                  N. Freed, Ed.
ISSN: 2070-1721                                                   Oracle
                                                            January 2013


        Internet Message Access Protocol (IMAP) - MOVE Extension

Abstract

   This document defines an IMAP extension consisting of two new
   commands, MOVE and UID MOVE, that are used to move messages from one
   mailbox to another.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6851.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.








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1.  Introduction

   This document defines an IMAP [RFC3501] extension to facilitate
   moving messages from one mailbox to another.  This is accomplished by
   defining a new MOVE command and extending the UID command to allow
   UID MOVE.

   A move function is not provided in the base IMAP specification, so
   clients have instead had to use a combination of the COPY, STORE, and
   EXPUNGE commands to perform this very common operation.

   Implementors have long pointed out some shortcomings with this
   approach.  Because the moving of a message is not an atomic process,
   interruptions can leave messages in intermediate states.  Because
   multiple clients can be accessing the mailboxes at the same time,
   clients can see messages in intermediate states even without
   interruptions.  If the source mailbox contains other messages that
   are flagged for deletion, the third step can have the side effect of
   expunging more than just the set of moved messages.  Additionally,
   servers with certain types of back-end message stores might have
   efficient ways of moving messages, which don't involve the actual
   copying of data.  Such efficiencies are often not available to the
   COPY/STORE/EXPUNGE process.

   The MOVE extension is present in any IMAP implementation that returns
   "MOVE" as one of the supported capabilities to the CAPABILITY
   command.

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].

   Formal syntax is specified using ABNF [RFC5234].

   Example lines prefaced by "C:" are sent by the client and ones
   prefaced by "S:" by the server.













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3.  MOVE and UID MOVE

3.1.  MOVE Command

   Arguments: sequence set
              mailbox name

   Responses: no specific responses for this command

   Result: OK - move completed

           NO - move error: can't move those messages or to that name

           BAD - command unknown or arguments invalid

3.2.  UID MOVE Command

   This extends the first form of the UID command (see [RFC3501],
   Section 6.4.8) to add the MOVE command defined above as a valid
   argument.

3.3.  Semantics of MOVE and UID MOVE

   The MOVE command takes two arguments: a message set (sequence numbers
   for MOVE, UIDs for UID MOVE) and a named mailbox.  Each message
   included in the set is moved, rather than copied, from the selected
   (source) mailbox to the named (target) mailbox.

   This means that a new message is created in the target mailbox with a
   new UID, the original message is removed from the source mailbox, and
   it appears to the client as a single action.  This has the same
   effect for each message as this sequence:

   1.  [UID] COPY

   2.  [UID] STORE +FLAGS.SILENT \DELETED

   3.  UID EXPUNGE

   Although the effect of the MOVE is the same as the preceding steps,
   the semantics are not identical: The intermediate states produced by
   those steps do not occur, and the response codes are different.  In
   particular, though the COPY and EXPUNGE response codes will be
   returned, response codes for a STORE MUST NOT be generated and the
   \DELETED flag MUST NOT be set for any message.






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   Because a MOVE applies to a set of messages, it might fail partway
   through the set.  Regardless of whether the command is successful in
   moving the entire set, each individual message SHOULD either be moved
   or unaffected.  The server MUST leave each message in a state where
   it is in at least one of the source or target mailboxes (no message
   can be lost or orphaned).  The server SHOULD NOT leave any message in
   both mailboxes (it would be bad for a partial failure to result in a
   bunch of duplicate messages).  This is true even if the server
   returns a tagged NO response to the command.

   Because of the similarity of MOVE to COPY, extensions that affect
   COPY affect MOVE in the same way.  Response codes such as TRYCREATE
   (see [RFC3501], Section 6.4.7), as well as those defined by
   extensions, are sent as appropriate.  See Section 4 for more
   information about how MOVE interacts with other IMAP extensions.

   An example:

       C: a UID MOVE 42:69 foo
       S: * OK [COPYUID 432432 42:69 1202:1229]
       S: * 22 EXPUNGE
       S: (more expunges)
       S: a OK Done

   Note that the server may send unrelated EXPUNGE responses as well, if
   any happen to have been expunged at the same time; this is normal
   IMAP operation.

   Implementers will need to read [RFC4315] to understand what UID
   EXPUNGE does, though full implementation of [RFC4315] is not
   necessary.

   Note that moving a message to the currently selected mailbox (that
   is, where the source and target mailboxes are the same) is allowed
   when copying the message to the currently selected mailbox is
   allowed.

   The server may send EXPUNGE (or VANISHED) responses before the tagged
   response, so the client cannot safely send more commands with message
   sequence number arguments while the server is processing MOVE or UID
   MOVE.

   Both MOVE and UID MOVE can be pipelined with other commands, but care
   has to be taken.  Both commands modify sequence numbers and also
   allow unrelated EXPUNGE responses.  The renumbering of other messages
   in the source mailbox following any EXPUNGE response can be
   surprising and makes it unsafe to pipeline any command that relies on
   message sequence numbers after a MOVE or UID MOVE.  Similarly, MOVE



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   cannot be pipelined with a command that might cause message
   renumbering.  See [RFC3501], Section 5.5, for more information about
   ambiguities as well as handling requirements for both clients and
   servers.

4.  Interaction with Other Extensions

   This section describes how MOVE interacts with some other IMAP
   extensions.

4.1.  RFC 2087, QUOTA

   The QUOTA extension (defined by [RFC2087]) may interact with MOVE on
   some servers, in the sense that a MOVE command may succeed where COPY
   would cause a quota overrun.

4.2.  RFC 4314, Access Control List (ACL)

   The ACL rights [RFC4314] required for MOVE and UID MOVE are the union
   of the ACL rights required for UID STORE, UID COPY, and UID EXPUNGE.

4.3.  RFC 4315, UIDPLUS

   Servers supporting UIDPLUS [RFC4315] SHOULD send COPYUID in response
   to a UID MOVE command.  For additional information see Section 3 of
   [RFC4315].

   Servers implementing UIDPLUS are also advised to send the COPYUID
   response code in an untagged OK before sending EXPUNGE or moved
   responses.  (Sending COPYUID in the tagged OK, as described in the
   UIDPLUS specification, means that clients first receive an EXPUNGE
   for a message and afterwards COPYUID for the same message.  It can be
   unnecessarily difficult to process that sequence usefully.)

4.4.  RFC 5162, QRESYNC

   The QRESYNC extension [RFC5162] states that the server SHOULD send
   VANISHED rather than EXPUNGE in response to the UID EXPUNGE command.
   The same requirement applies to MOVE, and a QRESYNC-enabled client
   needs to handle both VANISHED and EXPUNGE responses to a UID MOVE
   command.

   If the server is capable of storing modification sequences for the
   selected mailbox, it MUST increment the per-mailbox mod-sequence if
   at least one message was permanently moved due to the execution of
   the MOVE/UID MOVE command.  For each permanently removed message, the
   server MUST remember the incremented mod-sequence and corresponding
   UID.  If at least one message was moved, the server MUST send the



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   updated per-mailbox modification sequence using the HIGHESTMODSEQ
   response code (defined in [RFC4551]) in the tagged or untagged OK
   response.

   When one or more messages are moved to a target mailbox, if the
   server is capable of storing modification sequences for the mailbox,
   the server MUST generate and assign new modification sequence numbers
   to the moved messages that are higher than the highest modification
   sequence of the messages originally in the mailbox.

4.5.  IMAP Events in Sieve

   MOVE applies to IMAP events in Sieve [RFC6785] in the same way as
   COPY does.  Therefore, MOVE can cause a Sieve script to be invoked
   with the imap.cause set to "COPY".  Because MOVE does not cause flags
   to be changed, a MOVE command will not result in a script invocation
   with the imap.cause set to "FLAG".

5.  Formal Syntax

   The following syntax specification uses the Augmented Backus-Naur
   Form (ABNF) notation as specified in [RFC5234].  [RFC3501] defines
   the non-terminals "capability", "command-select", "sequence-set", and
   "mailbox".

   Except as noted otherwise, all alphabetic characters are case
   insensitive.  The use of upper or lower case characters to define
   token strings is for editorial clarity only.  Implementations MUST
   accept these strings in a case-insensitive fashion.

   capability     =/ "MOVE"

   command-select =/ move
   move           = "MOVE" SP sequence-set SP mailbox
   uid            = "UID" SP (copy / fetch / search / store / move)

6.  Security Considerations

   MOVE does not introduce any new capabilities to IMAP, and this limits
   the security impact.  However, the transactional semantics of MOVE
   may interact with specific implementations in ways that could have
   unexpected consequences.  For example, moving messages between
   mailboxes under the quota root may require temporary suspension of
   quota checking.

   An additional area of concern is interaction with antispam,
   antivirus, and other security scanning and auditing mechanisms.
   Different mailboxes may have different security policies that could



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   interact with MOVE in complex ways.  Scanning with updated rules may
   also be required when messages are moved even when the underlying
   policy has not changed.

   MOVE does relieve a problem with the base specification, since client
   authors currently have to devise and implement complicated algorithms
   to handle partial failures of the STORE/COPY/EXPUNGE trio.
   Incomplete or improper implementation of these algorithms can lead to
   mail loss.

7.  IANA Considerations

   The IANA has added MOVE to the "IMAP 4 Capabilities" registry,
   <http://www.iana.org/assignments/imap4-capabilities>.

8.  Acknowledgments

   This document is dedicated to the memory of Mark Crispin, the
   inventor of the IMAP protocol, author of the IMAP protocol
   specification [RFC3501], and contributor to many other email
   specifications in the IETF.

   An extension like this has been proposed many times, by many people.
   This document is based on several of those proposals, most recently
   that by Witold Krecicki.  Witold, Benoit Claise, Adrien W. de Croy,
   Stephen Farrell, Bron Gondwana, Dan Karp, Christian Ketterer, Murray
   Kucherawy, Jan Kundrat, Barry Leiba, Alexey Melnikov, Kathleen
   Moriarty, Zoltan Ordogh, Pete Resnick, Timo Sirainen, Michael
   Slusarz, and others provided valuable comments.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, March 2003.

   [RFC4314]  Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
              RFC 4314, December 2005.

   [RFC4315]  Crispin, M., "Internet Message Access Protocol (IMAP) -
              UIDPLUS extension", RFC 4315, December 2005.






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   [RFC4551]  Melnikov, A. and S. Hole, "IMAP Extension for Conditional
              STORE Operation or Quick Flag Changes Resynchronization",
              RFC 4551, June 2006.

   [RFC5162]  Melnikov, A., Cridland, D., and C. Wilson, "IMAP4
              Extensions for Quick Mailbox Resynchronization", RFC 5162,
              March 2008.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

9.2.  Informative References

   [RFC2087]  Myers, J., "IMAP4 QUOTA extension", RFC 2087,
              January 1997.

   [RFC6785]  Leiba, B., "Support for Internet Message Access Protocol
              (IMAP) Events in Sieve", RFC 6785, November 2012.

Authors' Addresses

   Arnt Gulbrandsen
   Schweppermannstr. 8
   D-81671 Muenchen
   Germany

   Fax:   +49 89 4502 9758
   EMail: arnt@gulbrandsen.priv.no


   Ned Freed (editor)
   Oracle
   800 Royal Oaks
   Monrovia, CA  91016-6347
   USA

   EMail: ned+ietf@mrochek.com














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