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

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 (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
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   IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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