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 © 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

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

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.

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/

9. Full Copyright Statement

Copyright © 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.

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Acknowledgement

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