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PROPOSED STANDARD
Network Working Group                                        A. Melnikov
Request for Comments: 3691                                    Isode Ltd.
Category: Standards Track                                  February 2004
Internet Message Access Protocol (IMAP) UNSELECT command

Status of this Memo

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

This document defines an UNSELECT command that can be used to close the current mailbox in an Internet Message Access Protocol - version 4 (IMAP4) session without expunging it. Certain types of IMAP clients need to release resources associated with the selected mailbox without selecting a different mailbox. While IMAP4 provides this functionality (via a SELECT command with a nonexistent mailbox name or reselecting the same mailbox with EXAMINE command), a more clean solution is desirable.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. UNSELECT command . . . . . . . . . . . . . . . . . . . . . . . 2
3. Security Considerations. . . . . . . . . . . . . . . . . . . . 3
4. Formal Syntax. . . . . . . . . . . . . . . . . . . . . . . . . 3
5. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 3
6. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 3
7. Normative References . . . . . . . . . . . . . . . . . . . . . 4
8. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 4
9. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 5
Melnikov                    Standards Track                     [Page 1]

RFC 3691                 IMAP UNSELECT command             February 2004
1.  Introduction
Certain types of IMAP clients need to release resources associated with the selected mailbox without selecting a different mailbox. While [IMAP4] provides this functionality (via a SELECT command with a nonexistent mailbox name or reselecting the same mailbox with EXAMINE command), a more clean solution is desirable.

[IMAP4] defines the CLOSE command that closes the selected mailbox as well as permanently removes all messages with the \Deleted flag set.

However [IMAP4] lacks a command that simply closes the mailbox without expunging it. This document defines the UNSELECT command for this purpose.

A server which supports this extension indicates this with a capability name of "UNSELECT".

"C:" and "S:" in examples show lines sent by the client and server respectively.

The keywords "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in this document when typed in uppercase are to be interpreted as defined in "Key words for use in RFCs to Indicate Requirement Levels" [KEYWORDS].
2.  UNSELECT Command
Arguments: none

Responses: no specific responses for this command

Result: OK - unselect completed, now in authenticated state
BAD - no mailbox selected, or argument supplied but
none permitted

The UNSELECT command frees server's resources associated with the selected mailbox and returns the server to the authenticated state. This command performs the same actions as CLOSE, except that no messages are permanently removed from the currently selected mailbox.

Example: C: A341 UNSELECT
S: A341 OK Unselect completed
Melnikov                    Standards Track                     [Page 2]

RFC 3691                 IMAP UNSELECT command             February 2004
3.  Security Considerations
It is believed that this extension doesn't raise any additional security concerns not already discussed in [IMAP4].
4.  Formal Syntax
The following syntax specification uses the Augmented Backus-Naur Form (ABNF) notation as specified in [ABNF]. Non-terminals referenced but not defined below are as defined by [IMAP4].

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.

command-select /= "UNSELECT"
5.  IANA Considerations
IMAP4 capabilities are registered by publishing a standards track or IESG approved experimental RFC. The registry is currently located at:

http://www.iana.org/assignments/imap4-capabilities

This document defines the UNSELECT IMAP capabilities. IANA has added this capability to the registry.
6.  Acknowledgments
UNSELECT command was originally implemented by Tim Showalter in Cyrus IMAP server.

Also, the author of the document would like to thank Vladimir Butenko and Mark Crispin for reminding that UNSELECT has to be documented. Also thanks to Simon Josefsson for pointing out that there are multiple ways to implement UNSELECT.
Melnikov                    Standards Track                     [Page 3]

RFC 3691                 IMAP UNSELECT command             February 2004
7.  Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[IMAP4] Crispin, M., "Internet Message Access Protocol - Version
4rev1", RFC 3501, March 2003.

[ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
8.  Author's Address
Alexey Melnikov Isode Limited 5 Castle Business Village Hampton, Middlesex TW12 2BX

EMail: Alexey.Melnikov@isode.com URI: http://www.melnikov.ca/
Melnikov                    Standards Track                     [Page 4]

RFC 3691                 IMAP UNSELECT command             February 2004
9.  Full Copyright Statement
Copyright (C) The Internet Society (2004). 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.

Intellectual Property

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.

Acknowledgement

Funding for the RFC Editor function is currently provided by the Internet Society.









Melnikov Standards Track [Page 5]

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