Network Working Group Arnt Gulbrandsen
Internet-Draft March 2012
Intended Status: Proposed Standard
The IMAP Move Extension
draft-gulbrandsen-imap-move-01.txt
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Abstract
The MOVE extension provides a new command, UID MOVE, which moves one
or more messages from the selected mailbox to a named mailbox.
1. 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 defined by [RFC5234].
Example lines prefaced by "C:" are sent by the client and ones
prefaced by "S:" by the server.
2. Overview
This document defines an IMAP extension to move messages atomically
from one mailbox to another. This function (very common in MUA UIs)
is not provided by stock IMAP, and clients have to use a combination
of UID STORE, UID COPY and EXPUNGE, and cope with partial failures.
Only UID MOVE is defined, not MOVE. There are three reasons for this.
First, MOVE poses some difficult questions with regard to expunges.
Second, in a survey of user agents that provide move in the user
interface, all were seen to use UID commands anyway. Third, a server
implementer reported that MSN-based move would be more difficult than
UID MOVE.
If MSN-based move is found to be needed (rather than neat), it can be
defined by a future document.
3. UID MOVE
The UID MOVE command takes two arguments: a set of UIDs and a named
mailbox. It moves each message indicated by UID set to the named
mailbox.
The UID MOVE command is the same as a sequence of UID COPY, UID STORE
+FLAGS \DELETED and UID EXPUNGE, with two added requirements:
First, each message SHOULD either be moved or unaffected. The server
SHOULD NOT leave a message in neither or both mailboxes afterwards
(even if the server returns a tagged NO response).
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Second, the messages MUST NOT have the \Deleted flag set in the
target mailbox.
An example:
C: a UID MOVE 42:69 forble
@S: a OK [COPYUID 432432 1202:1229] Done
4. Interaction with other extensions
This section is informational. There are no requirements in this
section; it only points out how other documents interact with this.
The QUOTA extension 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.
Since UID MOVE is defined as equivalent to UID STORE, UID COPY and
UID EXPUNGE, it requires the same ACL rights as the union of those
three commands.
Since UID MOVE is defined by reference to UID COPY, the server may
send COPYUID for UID MOVE, just as for UID COPY.
5. Reasons to avoid this extension
Servers may want to avoid implementing this because atomicity
requires holding one or more locks on several mailboxes at the same
time. Maildir-based servers, in particular, might have problems
locking sufficiently if the source and target mailboxes are on
different file systems.
Clients may want to avoid implementing this if they already have a
complex fallback/restart algorithm, and want to have it used, so that
any problems are easily visible.
Fixme: Either unfuck this entire section or drop it. I would prefer
to drop it.
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6. Formal Syntax
The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in [RFC5234]. [RFC3501] defines the
non-terminals "capability" and "command".
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 =/ "UID MOVE" SP set SP mailbox
7. Security Considerations
This document is believed to add no security problems. It does
however relieve a problem with the base specification, since client
authors have to devise and implement complicated algorithms to handle
partial failures of the STORE/COPY/EXPUNGE trio. Problems with these
algorithms can lead to mail loss.
8. IANA Considerations
The IANA is requested to add MOVE to the list of IMAP extensions,
http://www.iana.org/assignments/imap4-capabilities.
9. Acknowledgements
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, Alexey Melnikov, Bron Gondwana, Adrien W. de
Croy and others provided valuable comments.
10. Normative References
[RFC2119] Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, Harvard University, March
1997.
[RFC3501] Crispin, "Internet Message Access Protocol - Version
4rev1", RFC 3501, University of Washington, June 2003.
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[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 5234, January 2008.
11. Author's Address
Arnt Gulbrandsen
Schweppermannstr. 8
D-81671 Muenchen
Germany
Fax: +49 89 4502 9758
Email: arnt@gulbrandsen.priv.no
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(RFC Editor: Please delete everything after this point)
Open Issues
Only those noted as "fixme" in the text.
Changes since -00
- Fixed two bad nouns. Mailboxes aren't messages.
- Adrien's server can easily do UID MOVE but not so easily MSN-based
moves.
Changes since -01
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