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Internet Engineering Task Force (IETF)                    A. GulbrandsenRequest for Comments: 6851Category: Standards Track                                  N. Freed, Ed.ISSN: 2070-1721                                                   Oracle                                                            January 2013Internet Message Access Protocol (IMAP) - MOVE ExtensionAbstract   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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://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 toBCP 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 20131.  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 20133.  MOVE and UID MOVE3.1.  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 invalid3.2.  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.  SeeSection 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, MOVEGulbrandsen & 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 seeSection 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 theGulbrandsen & 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 couldGulbrandsen & 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.  References9.1.  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.comGulbrandsen & Freed          Standards Track                    [Page 8]