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rfc:rfc6851

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.

Gulbrandsen & Freed Standards Track [Page 1] RFC 6851 IMAP - MOVE Extension January 2013

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.

Gulbrandsen & Freed Standards Track [Page 2] RFC 6851 IMAP - MOVE Extension January 2013

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.

Gulbrandsen & Freed Standards Track [Page 3] RFC 6851 IMAP - MOVE Extension January 2013

 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

Gulbrandsen & Freed Standards Track [Page 4] RFC 6851 IMAP - MOVE Extension January 2013

 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

Gulbrandsen & Freed Standards Track [Page 5] RFC 6851 IMAP - MOVE Extension January 2013

 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

Gulbrandsen & Freed Standards Track [Page 6] RFC 6851 IMAP - MOVE Extension January 2013

 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.

Gulbrandsen & Freed Standards Track [Page 7] RFC 6851 IMAP - MOVE Extension January 2013

 [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

Gulbrandsen & Freed Standards Track [Page 8]

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