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Versions: (draft-melnikov-imap-expunged) 00 01 02 03 04 05 06 RFC 5162

Network Working Group                                        A. Melnikov
Internet-Draft                                                 Isode Ltd
Intended status: Standards Track                             D. Cridland
Expires: December 3, 2006                          Inventure Systems Ltd
                                                               C. Wilson
                                                                   Nokia
                                                               June 2006


          IMAP4 Extensions for Quick Mailbox Resynchronization
              draft-ietf-lemonade-reconnect-client-01.txt

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   This Internet-Draft will expire on December 3, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document defines an IMAP4 extension, which gives an IMAP client
   the ability to quickly resynchronize any previously opened mailbox as
   part of the SELECT command, without the need for server-side state or
   additional client round-trips.




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Changes since draft-ietf-lemonade-reconnect-client-01.txt

   o  If client's UIDVALIDITY doesn't match server's, the server will
      not return any flags anymore.

   o  Clarified that SELECT (QRESYNC) is a CONDSTORE-enabling command.

   o  Other minor editorial changes and fixes.

Changes since draft-ietf-lemonade-reconnect-client-00.txt

   o  Changed server behavior when the specified UIDVALIDITY doesn't
      match the current.  This allows the client to chose how to proceed
      after that.

   o  Other minor editorial changes and fixes.



































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Table of Contents

   1.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction and Overview  . . . . . . . . . . . . . . . . . .  4
   3.  Quick resynchronization extension  . . . . . . . . . . . . . .  5
     3.1.  QRESYNC parameter to SELECT/EXAMINE  . . . . . . . . . . .  5
   4.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   7.  Normative References . . . . . . . . . . . . . . . . . . . . .  8
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  8
   Intellectual Property and Copyright Statements . . . . . . . . . . 10







































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1.  Requirements notation

   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].

   In examples, "C:" and "S:" indicate lines sent by the client and
   server respectively.  If a single "C:" or "S:" label applies to
   multiple lines, then the line breaks between those lines are for
   editorial clarity only and are not part of the actual protocol
   exchange.


2.  Introduction and Overview

   IMAP [CONDSTORE] extension provides a way to quickly resynchronize
   changes to IMAP flags since a known moment.  This can be done using
   FETCH modifier once a mailbox is opened.

   The [EXPUNGED] IMAP extension allows to quickly discover expunged
   messages.

   The IMAP extension described in this document combines functionality
   provided by both [CONDSTORE] and [EXPUNGED] extensions, while
   reducing one more round-trip.

   In particular this extension can be useful for mobile clients that
   can experience frequent disconnects caused by environmental factors
   (battery life, signal strength, etc.).  Such clients would need a way
   to quickly reconnect to the IMAP server, without forcing the user to
   experience long delay and pay big bills for the amount of traffic
   generated by resynchronization.

   By extending the SELECT command to perform the additional
   resynchronization, this also allows clients to reduce concurrent
   connections to the IMAP server held purely for the sake of avoiding
   the resynchronization.

   [[anchor3: Note to RFC editor: This document is compliant with
   "transitional IMAP capabilities" document [TRANS-CAPA].  Please
   change the capability name below to "QRESYNC"]]

   The quick resync IMAP extension is present if an IMAP4 server returns
   "X-DRAFT-W01-QRESYNC" as one of the supported capabilities to the
   CAPABILITY command.  Note, that this extension REQUIREs support for
   the [CONDSTORE] and the [EXPUNGED] IMAP extensions, so they MUST be
   announced in the CAPABILITY response as well.




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3.  Quick resynchronization extension

3.1.  QRESYNC parameter to SELECT/EXAMINE

   The Quick Resynchronization parameter to SELECT/EXAMINE commands has
   three arguments:

   o  the last known UIDVALIDITY,

   o  the last known modification sequence

   o  and the optional list of known UIDs.

   The parameter acts as a CONDSTORE enabling command, as defined in
   [CONDSTORE].  In other words, the use of the QRESYNC parameter
   implies the CONDSTORE parameter.  Also, the QRESYNC parameter implies
   the EXPUNGED parameter, as defined in [EXPUNGED].

   Before opening the specified mailbox the server verifies all
   arguments for syntactic validity.  If any parameter is not
   syntactically valid, the server return the tagged BAD response, and
   the mailbox remains unselected.  Once the check is done the server
   opens the mailbox as if no SELECT/EXAMINE parameters are specified
   (this is subject to processing of other parameters as defined in
   other extensions).  In particular this means that server MUST send
   all untagged responses as specified in Section 6.3.1/6.3.2 of
   [RFC3501].

   After that the server checks the UIDVALIDITY value provided by the
   client.  If the provided UIDVALIDITY doesn't match the UIDVALIDITY
   for the mailbox being opened, then the server MUST ignore the
   remaining parameters and behave as if no dynamic message data
   changed.  The client can discover this situation by comparing the
   UIDVALIDITY value returned by the server.  This behaviour allows the
   client not to synchronize the mailbox or decide on the best
   synchronization strategy.

   Example: Attempting to resynchronize INBOX, but the provided
            UIDVALIDITY parameter doesn't match the current UIDVALIDITY
            value.

            C: A02 SELECT INBOX (QRESYNC (67890007 20050715194045000
            41,43:211,214:541))
            S: * 464 EXISTS
            S: * 3 RECENT
            S: * OK [UIDVALIDITY 3857529045] UIDVALIDITY
            S: * OK [UIDNEXT 550] Predicted next UID
            S: * OK [HIGHESTMODSEQ 20060128194045007]



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            S: * OK [UNSEEN 12] Message 12 is first unseen
            S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen)
            S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft
            \Deleted \Seen \*)] Permanent flags
            S: A02 OK [READ-WRITE] Sorry, UIDVALIDITY mismatch

   Modification Sequence and UID Parameters:

   If the provided UIDVALIDITY matches that of the selected mailbox, the
   server then checks the last known modification sequence.
   The server sends the client any pending flag changes (using FETCH
   responses that MUST contain UIDs) and expunges that have occurred in
   this mailbox since the provided modification sequence.

   If the list of known UIDs was also provided, the server should only
   report flag changes and expunges for the provided messages.  If the
   client doesn't provide the list of UIDs, the server acts as if the
   client has specified "1:*".

   Thus, the client client can process just these pending events and
   need not perform a full resynchronization.  The result of this step
   is semantically equivalent to the client issuing:
   tag1 UID FETCH "known-uids" (FLAGS) (CHANGEDSINCE
   "mod-sequence-value" REPORTEXPUNGES)

   Example:

      C: A02 SELECT INBOX (QRESYNC (67890007
         20060115194045000 41,43:211,214:541))

      S: * 314 EXISTS

      S: 15 RECENT

      S: * OK [UIDVALIDITY 67890007] UIDVALIDITY

      S: * OK [UIDNEXT 567] Predicted next UID

      S: * OK [HIGHESTMODSEQ 20060115205545359]

      S: * OK [UNSEEN 7] There are some unseen messages in the mailbox

      S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen)

      S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft
         \Deleted \Seen \*)] Permanent flags





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      S: * 49 FETCH (UID 117 FLAGS (\Seen \Answered))

      S: * 50 FETCH (UID 119 FLAGS (\Draft $MDNSent))

      S: ...

      S: * 100 FETCH (UID 541 FLAGS (\Seen $Forwarded))

      S: * EXPUNGED 41,43:116,118,120:211,214:540

      S: A02 OK [READ-WRITE] mailbox selected


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
   [RFC3501], [CONDSTORE], [EXPUNGED] or [IMAPABNF].

   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.

   select-param     = "QRESYNC" SP "(" uidvalidity SP
                      mod-sequence-value [SP known-uids] ")"
                      ;; conforms to the generic select-param
                      ;; syntax defined in [IMAPABNF]

   uidvalidity      = nz-number

   known-uids       = sequence-set
                      ;; sequence of UIDs, "*" is not allowed


5.  Security Considerations

   Security considerations relevant to [CONDSTORE] and [EXPUNGED] are
   relevant to this extension.

   This document doesn't raise any new security concerns not already
   raised by [CONDSTORE].







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6.  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 X-DRAFT-W01-QRESYNC [[anchor9: The final
   capability name will be chosen during AUTH48]] IMAP capability.  IANA
   is requested to add this capability to the registry.


7.  Normative References

   [ABNF]     Crocker, D., Ed. and P. Overell, Ed., "Augmented BNF for
              Syntax Specifications: ABNF", RFC 4234, October 2005.

   [CONDSTORE]
              Melnikov, A. and S. Hole, "IMAP Extension for Conditional
              STORE Operation or Quick Flag Changes Resynchronization",
              RFC 4551, June 2006.

   [EXPUNGED]
              Melnikov, A., "IMAP4 extension for reporting expunged
              messages", June 2006.

   [IMAPABNF]
              Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4
              ABNF", RFC 4466, April 2006.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, March 2003.















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Authors' Addresses

   Alexey Melnikov
   Isode Ltd
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   Email: Alexey.Melnikov@isode.com


   Dave Cridland
   Inventure Systems Ltd
   21, Heol Bronwydd
   Caerfyrddin, Cymru  SA31 2AJ
   GB

   Email: dave.cridland@invsys.co.uk


   Corby Wilson
   Nokia
   5 Wayside Rd.
   Burlington, MA  01803
   USA

   Email: corby@computer.org























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Full Copyright Statement

   Copyright (C) The Internet Society (2006).

   This document is subject to the rights, licenses and restrictions
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