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Versions: (draft-gulbrandsen-imap-move) 00 01 02 03 04 05 RFC 6851

Network Working Group                                     A. Gulbrandsen
Internet-Draft
Intended status: Standards Track                                N. Freed
Expires: June 2, 2013                                             Oracle
                                                       November 29, 2012


        Internet Message Access Protocol (IMAP) - MOVE Extension
                     draft-ietf-imapmove-command-05

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 Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 2, 2013.

Copyright Notice

   Copyright (c) 2012 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
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   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.  And servers with
   certain types of back-end message stores might have efficient ways of
   moving messages, which don't involve actual copying of data.  Such
   efficiencies are often not available to the COPY/STORE/EXPUNGE
   process.

   The MOVE extension is present in any IMAP4 implementation which
   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.


3.  MOVE and UID MOVE









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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.

   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



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   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 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 forble
       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.  The
   UID MOVE command does not have this limitation.

   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 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.



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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, ACL

   The ACL rights [RFC4314] required for 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] MUST send COPYUID in response to
   a UID MOVE command.

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

   When a message is moved to a target mailbox, if the server is capable
   of storing modification sequences for the mailbox, the server MUST



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   generate a new modification sequence that is higher than the highest
   modification sequence of all messages in the mailbox and assign it to
   the moved message.

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 which could
   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.




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   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 is requested to add MOVE to the "IMAP 4 Capabilities"
   registry, http://www.iana.org/assignments/imap4-capabilities.


8.  Acknowledgments

   An extension like this has been proposed many times, by many people.
   This document is based on several of those, 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.

   [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.




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   [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.


Appendix A.  Change History

   RFC Editor: Please delete this section from the final RFC.

A.1.  Changes since -00

   1.  Fixed two bad nouns.  Mailboxes aren't messages.

   2.  Adrien's server can easily do UID MOVE but not so easily MSN-
       based moves.

A.2.  Changes since -01

   1.  Changed to Informative, on Barry's suggestion.  Or did I ask him?
       Whatever.

   2.  Removed the 'reasons to avoid', it was doubleplusungood.

A.3.  Changes since draft-gulbrandsen-imap-move-02

   1.  Various wording changes from Barry's review.

   2.  Open issue: Delete the \deleted rule?

   3.  Back to PS, informative didn't fly in the IESG

   4.  Turned into a WG document in order to get write access to the
       IMAP4 capabilities registry

   5.  Mention VANISHED in 5162

   6.  Added bad boilerplate to please idnits.  This document contains
       no code.






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A.4.  Changes since -00

   1.  Added MSN-based move.  The consensus seems mildly in favor.  I
       think.  We'll see once this is posted.

   2.  Advise sending COPYUID earlier, to help clients.  Requiring out
       of order processing is unnecessarily nasty.

   3.  Note that moving to the source inbox has to work.  I think it
       does have to work, but this is a draft, it says so on every page.

A.5.  Changes since -01

   1.   (Issue tracker #1) Changed command-select ABNF to conform with
        the conventions used in RFC 3501.

   2.   (Issue tracker #2) Banned overlapped pipelined MOVE and UID
        MOVE.

   3.   (Issue tracker #3) Added section about interaction with IMAP
        Sieve.

   4.   (Issue tracker #4) Revised security considerations.

   5.   (Issue tracker #5) Removed text that characterized MOVE as the
        same as COPY/STORE/EXPUNGE.

   6.   (Issue tracker #6) RFC 4314 is now a normative reference.

   7.   (Issue tracker #7) Major rewrite of the command description text
        as a result of AD review.

   8.   (Issue tracker #8) Revised abstract.

   9.   (Issue tracker #9) Added text saying partial failures are
        allowed.

   10.  (Issue tracker #10) Some additional tweaks to the security
        considerations section were made.

   11.  The abstract and introduction were out of whack as a result of
        other changes, so some revisions were made to bring them back
        into sync.








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A.6.  Changes since -02

   1.  Corrected various typos, clarified several paragraphs discussing
       MOVE semantics.

   2.  Added the usual text about the extension only being available
       when it is reported by the CAPABILITIES command.

   3.  Revised the text about QRESYNC to make clear what the
       requirements are.

   4.  Removed a suggestion about MUA/user behavior from the discussion
       of the QUOTA extension.

   5.  Updated the main and running title to conform to other IMAP RFCs.

A.7.  Changes since -03

   1.  Corrected another bad noun.  Responses aren't messages.

   2.  More minor editorial changes.

   3.  The text on command pipelining has been completely rewritten.

   4.  Added text stating that the effects of setting the \Deleted flag
       aren't visible.

A.8.  Changes since -04

   1.  Added some additional requirements text for QRESYNC.

   2.  Took some text from the charter and added it to the introduction
       in order to clarify why this extension is useful.


Authors' Addresses

   Arnt Gulbrandsen
   Schweppermannstr. 8
   D-81671 Muenchen
   Germany

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







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

   Email: ned+ietf@mrochek.com












































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