Network Working Group A. Gulbrandsen
Internet-Draft
Intended status: Standards Track N. Freed
Expires: April 23, 2013 Oracle
October 20, 2012
The IMAP Move Extension
draft-ietf-imapmove-command-02
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
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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 UID STORE, UID
COPY and EXPUNGE commands to perform this very common operation.
This has meant needing to cope with partial failures and side effects
that can occur when multiple commands are involved.
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
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.
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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
Each message SHOULD either be moved or unaffected. The server MUST
NOT leave a message in neither mailbox, and SHOULD NOT leave a
message in both mailboxes afterwards, even if the server returns a
tagged NO response. Note that these restrictions only apply to
individual messages and not to the command as a whole, which can fail
partway through.
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 EXPUNGEs for other messages 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
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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) messages 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, however, pipelined MOVE and
UID MOVE commands MUST NOT specify overlapping sets of messages.
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. This may be user-visible, but should
not be MUA-visible.
4.2. RFC 4314, ACL
The ACL rights [RFC4314] required for the 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 for moved
messages. (Sending it 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 usefully.)
4.4. RFC 5162, QRESYNC
The QRESYNC extension [RFC5162] directs the server to send VANISHED
rather than EXPUNGE in response to the UID EXPUNGE command. The same
requirement applies to the UID MOVE command.
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4.5. IMAP Events in Sieve
MOVE applies to IMAP events in Sieve [I-D.ietf-sieve-imap-sieve] 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
folders 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 folders 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 with 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
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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, Adrien W. de Croy, Bron Gondwana, Dan Karp,
Barry Leiba, Alexey Melnikov, 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.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
9.2. Informative References
[I-D.ietf-sieve-imap-sieve]
Leiba, B., "Support for Internet Message Access Protocol
(IMAP) Events in Sieve", draft-ietf-sieve-imap-sieve-09
(work in progress), September 2012.
[RFC2087] Myers, J., "IMAP4 QUOTA extension", RFC 2087,
January 1997.
[RFC5162] Melnikov, A., Cridland, D., and C. Wilson, "IMAP4
Extensions for Quick Mailbox Resynchronization", RFC 5162,
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March 2008.
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.
A.4. Changes since -00
1. Added MSN-based move. The consensus seems mildly in favour. 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.
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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.
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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