Network Working Group Arnt Gulbrandsen
Request for Comments: DRAFT Oryx Mail Systems GmbH
September 2006
The IMAP ENABLE Extension
draft-gulbrandsen-imap-enable-00.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-
Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire in March, 2007.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
The ENABLE extension allows an IMAP client to enable certain IMAP
extensions explicitly.
1. Conventions Used in This Document
The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD
Gulbrandsen Expires March 2007 [Page 1]
Internet-draft September 2006
NOT", and "MAY" in this document are to be interpreted as described
in "Key words for use in RFCs to Indicate Requirement Levels"
[KEYWORDS]. Formal syntax is defined by [ABNF] as modified by [IMAP]
and [IMAPABNF].
Example lines prefaced by "C:" are sent by the client and ones
prefaced by "S:" by the server. The five characters [...] means that
something has been elided.
2. Overview
[CONDSTORE], [ANNOTATE] and some extensions under consideration at
the moment use various commands to enable server extensions.
CONDSTORE, for example, uses a SELECT or FETCH parameter. However,
SELECT starts a session and FETCH fetches messages. This extension
adds a command, ENABLE, which enables such extensions without
causing any other effect.
An IMAP server which supports ENABLE advertises this by including
the word ENABLE in its capability list.
3. The ENABLE Command
Arguments: capability names
Result: OK: Relevant capabilities enabled
BAD: No arguments, or syntax error in an argument
The ENABLE command takes a list of capability names, and requests
the server to enable the named extensions. Once enabled using
ENABLE, each extension remains active until the IMAP connection is
closed. For each argument, the server does the following:
- If the argument is not an extension known to the server, the
server MUST ignore the argument.
- If the argument is an extension known to the server, and it does
not make sense to enable the extension in this way, the server
MUST ignore the argument. (For example, ENABLE ID does nothing
because [ID] does not need to be enabled in the server prior to
being used.)
- If the argument is an extension is supported by the server and
which needs to be enabled, the server MUST enable the extension
for the duration of the connection. At present this applies only
to CONDSTORE.
Gulbrandsen Expires March 2007 [Page 2]
Internet-draft September 2006
In this example, the client enables CONDSTORE:
C: a ENABLE CONDSTORE
S: a OK Conditional Store enabled
In the next example, the client asks about the server capabilities,
the server tells the client only what's usable prior to login, the
client enables CONDSTORE and X-GOOD-IDEA, then it logs in.
C: a CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=CRAM-MD5 AUTH=DIGEST-MD5 ID
LITERAL+
S: a OK foo
C: b ENABLE CONDSTORE X-GOOD-IDEA
S: b OK foo
C: c LOGIN d e
S: c OK foo C: d CAPABILITY
S: * CAPABILITY IMAP4rev1 ID LITERAL+ CONDSTORE
S: d OK foo
After command b, the client does not know whether CONDSTORE and X-
GOOD-IDEA are enabled. After command d, the client learns that the
server supports CONDSTORE but not X-GOOD-IDEA, so it knows that
CONDSTORE is enabled.
4. Formal Syntax
The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in [ABNF]. [IMAP] defines the non-
terminals "capability" and "command-any".
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 =/ "ENABLE"
command-any =/ "ENABLE" 1*(SP capability)
5. Security considerations
This document does not add any new security considerations to IMAP.
Gulbrandsen Expires March 2007 [Page 3]
Internet-draft September 2006
6. IANA considerations
The IANA is requested to add ENABLE to the list of IMAP extensions.
7. Credits
The idea for this draft came from Randy Gellens. Alexey Melnikov
thought it was a good idea. The author of this document typed it
down and added the open issues section.
8. Normative References
[ABNF] Crocker, Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, Brandenburg
Internetworking, Demon Internet Ltd, October 2005.
[KEYWORDS] Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, Harvard University, March
1997.
[IMAP] Crispin, "Internet Message Access Protocol - Version
4rev1", RFC 3501, University of Washington, June 2003.
[IMAPABNF] Melnikov, Daboo, "Collected Extensions to IMAP4 ABNF",
RFC 4466, Isode Ltd., April 2006.
8. Informative References
[CONDSTORE] Melnikov, Hole, "IMAP Extension for Conditional STORE
Operation or Quick Flag Changes Resynchronization", RFC
4551, Isode Ltd., June 2006.
[ID] Showalter, "IAMP4 ID extension", RFC 2971, Mirapoint
Inc., October 2000.
Gulbrandsen Expires March 2007 [Page 4]
Internet-draft September 2006
10. Author's Address
Arnt Gulbrandsen
Oryx Mail Systems GmbH
Schweppermannstr. 8
D-81671 Muenchen
Germany
Fax: +49 89 4502 9758
Email: arnt@oryx.com
Open Issues
[Note to RFC editor: Please delete before publishing.]
Is a DISABLE command necessary? Is there any benefit to it? Is there
any benefit to not having a DISABLE?
Is there any benefit to restricting the capabilities that can be
specified with ENABLE?
Should ENABLE be a command-nonauth, so clients have to declare their
desires right at the start? That might simplify some server
implementations, particularly proxies. Servers would have to ignore
any capability names they don't know.
At the moment a client can "enable" any capability, even ones not
advertised by the server. This allows a client to enable all it can
support right at the start, even though the server won't advertise
its capabilities until after LOGIN/STARTTLS.
Gulbrandsen Expires March 2007 [Page 5]
Internet-draft September 2006
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed
to pertain to the implementation or use of the technology described
in this document or the extent to which any license under such
rights might or might not be available; nor does it represent that
it has made any independent effort to identify any such rights.
Information on the procedures with respect to rights in RFC
documents can be found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use
of such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository
at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
Full Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Gulbrandsen Expires March 2007 [Page 6]
