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Versions: 00 01 02 draft-ietf-lemonade-reconnect-client

Network Working Group                                        A. Melnikov
Internet-Draft                                                 Isode Ltd
Intended status: Standards Track                        October 16, 2006
Expires: April 19, 2007


            IMAP4 extension for reporting expunged messages
                  draft-melnikov-imap-expunged-02.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
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   This Internet-Draft will expire on April 19, 2007.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document defines an IMAP extension, which gives a disconnected
   client ability to quickly learn about expunged messages.  This
   extension also introduces a new response that allows for a more
   compact representation for a list of expunged messages.







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Table of Contents

   1.  Conventions Used in this Document  . . . . . . . . . . . . . .  3
   2.  Introduction and Overview  . . . . . . . . . . . . . . . . . .  3
   3.  IMAP Protocol Changes  . . . . . . . . . . . . . . . . . . . .  4
     3.1.  REPORTEXPUNGES UID FETCH modifier  . . . . . . . . . . . .  4
     3.2.  REPORTEXPUNGES Parameter to SELECT and EXAMINE . . . . . .  5
     3.3.  EXPUNGE Command  . . . . . . . . . . . . . . . . . . . . .  6
     3.4.  CLOSE Command  . . . . . . . . . . . . . . . . . . . . . .  7
     3.5.  UID EXPUNGE Command  . . . . . . . . . . . . . . . . . . .  7
     3.6.  VANISHED Response  . . . . . . . . . . . . . . . . . . . .  9
   4.  Server implementation considerations . . . . . . . . . . . . . 11
     4.1.  Server implementations that don't store extra state  . . . 11
     4.2.  Additional state required on the server  . . . . . . . . . 11
   5.  Updated synchronization sequence . . . . . . . . . . . . . . . 12
   6.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . . 15
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 16
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     10.2. Informative References . . . . . . . . . . . . . . . . . . 17
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 17
   Intellectual Property and Copyright Statements . . . . . . . . . . 18



























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1.  Conventions Used in this Document

   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.

   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].

   Understanding of the IMAP message sequence numbers and UIDs and the
   EXPUNGE response [RFC3501] is essential when reading this document.

   [[anchor2: Editorial comments and questions are marked like this.]]


2.  Introduction and Overview

   The [CONDSTORE] extension gives a disconnected client ability to
   quickly synchronize IMAP flag changes for previously seen messages.
   In order for the client to discover which messages have been
   expunged, the client still has to issue a UID FETCH or a UID SEARCH
   command.  This document defines an extension to [CONDSTORE], that
   allows a reconnecting client to quickly learn about expunged
   messages.  This extension also introduces a new response VANISHED
   that allows for a more compact representation for a list of expunged
   messages.

   The Expunged Messages Notification extension is present in any IMAP4
   implementation which advertises "X-DRAFT-I02-EXPUNGED" [[anchor4:
   Change before publication]] as one of the supported capabilities in
   the CAPABILITY command response.  Any server returning the capability
   MUST also support the The [CONDSTORE] extension.

   This document puts additional requirements on a server implementing
   the [CONDSTORE] extension.  Each mailbox that supports persistent
   storage of mod-sequences, i.e., for which the server has sent a
   HIGHESTMODSEQ untagged OK response code on a successful SELECT/
   EXAMINE, MUST increment the per-mailbox mod-sequence when one or more
   messages are expunged due to EXPUNGE, UID EXPUNGE or CLOSE; the
   server MUST associate the incremented mod-sequence with the UIDs of
   the expunged messages.

   This change doesn't affect a client that only supports the CONDSTORE
   extension, however per-mailbox mod-sequence change due to expunges
   may force the client to send FETCH CHANGEDSINCE that will return no



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   data, thus forcing additional round-trip. [[anchor5: Is this Ok?]]
   [[anchor6: Should we have a separate per mailbox modseq (for expunged
   messages) just to address this issue?]]


3.  IMAP Protocol Changes

3.1.  REPORTEXPUNGES UID FETCH modifier

   [IMAPABNF] has extended the syntax of the FETCH and UID FETCH
   commands to include an optional FETCH modifier.  This document
   defines a new UID FETCH modifier: REPORTEXPUNGES.

   Note, that the REPORTEXPUNGES UID FETCH modifier is NOT allowed with
   a FETCH command.  The server MUST return a tagged BAD response if
   this response is specified as a modifier to the FETCH command.

   The REPORTEXPUNGES UID FETCH modifier MUST only be specified together
   with the CHANGEDSINCE UID FETCH modifier. [[anchor9: alternative:
   allow REPORTEXPUNGES by itself, this will mean report all expunged
   UIDs from the UID set specified in the UID FETCH.]]

   The REPORTEXPUNGES UID FETCH modifier instructs the server to report
   those messages from the UID set parameter that have been expunged and
   whose associated modsequence is larger than the specified
   modsequence.  That is, the client requests to be informed of messages
   from the specified set that were expunged since the specified
   modsequence.  Note that the modsequence associated with these
   messages was incremented when the messages were expunged (as
   described above).  The expunged messages are reported using the
   VANISHED response as described in Section 3.6, which MUST contain the
   TAG correlator.

   The REPORTEXPUNGES UID FETCH modifier also instructs the server to
   replace all further EXPUNGE responses with VANISHED responses.  The
   server MUST do this until the connection is closed.















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   Example 1: Without the REPORTEXPUNGES UID FETCH modifier a CONDSTORE-
   aware client [CONDSTORE] needs to issue separate commands to learn of
   flag changes and expunged messages since the last synchronization:

   C: s100 UID FETCH 300:500 (FLAGS) (CHANGEDSINCE 12345)
   S: * 1 FETCH (UID 404 MODSEQ (65402) FLAGS (\Seen))
   S: * 2 FETCH (UID 406 MODSEQ (75403) FLAGS (\Deleted))
   S: * 4 FETCH (UID 408 MODSEQ (29738) FLAGS ($NoJunk
       $AutoJunk $MDNSent))
   S: s100 OK FETCH completed
   C: s101 UID SEARCH 300:500
   S: * SEARCH 404 406 407 408 410 412
   S: s101 OK search completed

   Where 300 and 500 are the lowest and highest UIDs from client's
   cache.  The second SEARCH response tells the client that the messages
   with UIDs 407, 410 and 412 are still present, but their flags haven't
   changed since the specified modification sequence.

   Using the REPORTEXPUNGES UID FETCH modifier it is sufficient to issue
   only a single command:

   C: s100 UID FETCH 300:500 (FLAGS) (CHANGEDSINCE 12345
       REPORTEXPUNGES)
   S: * 1 FETCH (UID 404 MODSEQ (65402) FLAGS (\Seen))
   S: * 2 FETCH (UID 406 MODSEQ (75403) FLAGS (\Deleted))
   S: * 4 FETCH (UID 408 MODSEQ (29738) FLAGS ($NoJunk
       $AutoJunk $MDNSent))
   S: * VANISHED (TAG "s100") 300:310,405,411
   S: s100 OK FETCH completed

3.2.  REPORTEXPUNGES Parameter to SELECT and EXAMINE

   The X-DRAFT-I02-EXPUNGED extension defines a single optional select
   parameter, "REPORTEXPUNGES", which tells the server that it SHOULD
   start sending VANISHED responses (see Section 3.6) instead of EXPUNGE
   responses.  This change remains in effect until the connection is
   closed.

   [[anchor11: Note that if we want to make the REPORTEXPUNGES parameter
   to SELECT/EXAMINE also behave as if UID FETCH (REPORTEXPUNGES) were
   specified, then we need to add 3 extra arguments to the
   REPORTEXPUNGES parameter (a la QRESYNC): the last known UIDVALIDITY,
   the last known modification sequence and the optional list of known
   UIDs.]]






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3.3.  EXPUNGE Command

   Arguments:  none

   Responses:  untagged responses: EXPUNGE or VANISHED

   Result:   OK - expunge completed
             NO - expunge failure: can't expunge (e.g., permission
      denied)
             BAD - command unknown or arguments invalid

   This section updates the definition of the EXPUNGE command described
   in section 6.4.3 of [RFC3501].

   The EXPUNGE command permanently removes all messages that have the
   \Deleted flag set from the currently selected mailbox.  Before
   returning an OK to the client, those messages that are removed are
   reported using a VANISHED response or EXPUNGE responses.

   If the server is capable of storing modification sequences for the
   selected mailbox, it MUST increment the per-mailbox mod-sequence if
   at least one message was permanently removed due to the execution of
   the EXPUNGE command.  For each permanently removed message the server
   MUST remember the incremented mod-sequence and corresponding UID.  If
   at least one message got expunged, the server MUST send the updated
   per-mailbox modification sequence using the HIGHESTMODSEQ response
   code (defined in [CONDSTORE]) in the tagged OK response.


    Example:    C: A202 EXPUNGE
                S: * 3 EXPUNGE
                S: * 3 EXPUNGE
                S: * 5 EXPUNGE
                S: * 8 EXPUNGE
                S: A202 OK [HIGHESTMODSEQ 20010715194045319] expunged Ok

   Note: In this example, messages 3, 4, 7, and 11 had the \Deleted flag
   set.  See the description of the EXPUNGE response in [RFC3501] for
   further explanation.

   Note that once the VANISHED response is enabled on the connection the
   previous example might look like this:

    Example:    C: B202 EXPUNGE
                S: * VANISHED 405,407,410,425
                S: B202 OK [HIGHESTMODSEQ 20010715194045319] expunged Ok

   Here messages with message numbers 3, 4, 7 and 11 have respective



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   UIDs 405, 407, 410 and 425.

3.4.  CLOSE Command

   Arguments:  none

   Responses:  no specific responses for this command

   Result:   OK - close completed, now in authenticated state
             BAD - command unknown or arguments invalid

   This section updates the definition of the CLOSE command described in
   section 6.4.2 of [RFC3501].

   The CLOSE command permanently removes all messages that have the
   \Deleted flag set from the currently selected mailbox, and returns to
   the authenticated state from the selected state.  No untagged EXPUNGE
   (or VANISHED) responses are sent.

   If the server is capable of storing modification sequences for the
   selected mailbox, it MUST increment the per-mailbox mod-sequence if
   at least one message was permanently removed due to the execution of
   the CLOSE command.  For each permanently removed message the server
   MUST remember the incremented mod-sequence and corresponding UID.  If
   at least one message got expunged, the server MUST send the updated
   per-mailbox modification sequence using the HIGHESTMODSEQ response
   code (defined in [CONDSTORE]) in the tagged OK response.


      Example:    C: A202 CLOSE
                  S: A202 OK [HIGHESTMODSEQ 20010715194045319] done

3.5.  UID EXPUNGE Command

   Arguments:  message set

   Responses:  untagged responses: EXPUNGE or VANISHED

   Result:   OK - expunge completed
             NO - expunge failure: can't expunge (e.g., permission
      denied)
             BAD - command unknown or arguments invalid

   This section updates the definition of the UID EXPUNGE command
   described in section 2.1 of [UIDPLUS].  Servers that implement both
   [UIDPLUS] and X-DRAFT-I02-EXPUNGED extensions must implement UID
   EXPUNGE as described in this section.




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   The UID EXPUNGE command permanently removes from the currently
   selected mailbox all messages that both have the \Deleted flag set
   and have a UID that is included in the specified message set.  If a
   message either does not have the \Deleted flag set or has a UID that
   is not included in the specified message set, it is not affected.

   This command is particularly useful for disconnected mode clients.
   By using UID EXPUNGE instead of EXPUNGE when resynchronizing with the
   server, the client can avoid inadvertently removing any messages that
   have been marked as \Deleted by other clients between the time that
   the client was last connected and the time the client resynchronizes.

   If the server does not support the UIDPLUS capability, the client
   SHOULD fall back to using the STORE command to temporarily remove the
   \Deleted flag from messages it does not want to remove, then issuing
   the EXPUNGE command.  Finally, the client SHOULD use the STORE
   command to restore the \Deleted flag on the messages in which it was
   temporarily removed.

   Alternatively, the client MAY fall back to using just the EXPUNGE
   command, risking the unintended removal of some messages.

   Before returning an OK to the client, those messages that are removed
   are reported using a VANISHED response or EXPUNGE responses.

   If the server is capable of storing modification sequences for the
   selected mailbox, it MUST increment the per-mailbox mod-sequence if
   at least one message was permanently removed due to the execution of
   the UID EXPUNGE command.  For each permanently removed message the
   server MUST remember the incremented mod-sequence and corresponding
   UID.  If at least one message got expunged, the server MUST send the
   updated per-mailbox modification sequence using the HIGHESTMODSEQ
   response code (defined in [CONDSTORE]) in the tagged OK response.


   Example:    C: . UID EXPUNGE 3000:3002
               S: * 3 EXPUNGE
               S: * 3 EXPUNGE
               S: * 3 EXPUNGE
               S: . OK [HIGHESTMODSEQ 20010715194045319] Ok

   Note: In this example, at least messages with message numbers 3, 4,
   and 5 (UIDs 3000 to 3002) had the \Deleted flag set.  See the
   description of the EXPUNGE response in [RFC3501] for further
   explanation.






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3.6.  VANISHED Response

   Contents:  optional correlators

              list of UIDs

   The VANISHED response reports that the specified UIDs have been
   permanently removed from the mailbox.  This response is similar to
   the EXPUNGE response [RFC3501], however it can return information
   about multiple messages and it returns UIDs instead of message
   numbers.  The first benefit saves bandwidth, while the second is more
   convenient for clients which only use UIDs to access the IMAP server.

   The VANISHED response has the same restrictions on when it can be
   sent as does the EXPUNGE response (see below).

   The VANISHED response starts with an optional correlator.  If it is
   present and contains the TAG correlator type, then the response is a
   result of a UID FETCH (REPORTEXPUNGES) command.  Other correlators
   can be added in the future.

   The VANISHED response is sent as a result of a UID FETCH
   (REPORTEXPUNGES) command, if the UID set parameter to the UID FETCH
   (REPORTEXPUNGES) command includes UIDs of messages that are no longer
   in the mailbox.  Such VANISHED response MUST contain the TAG
   correlator.

   Once a client has used "(REPORTEXPUNGES)" with a UID FETCH or SELECT/
   EXAMINE command, the server SHOULD use the VANISHED response instead
   of the EXPUNGE response.  The server SHOULD continue using VANISHED
   in lieu of EXPUNGE for the duration of the connection.  In particular
   this affects the EXPUNGE [RFC3501] and UID EXPUNGE [UIDPLUS]
   commands, as well as messages expunged in other connections.  Such
   VANISHED response MUST NOT contain the TAG correlator.

   A VANISHED response sent because of an EXPUNGE or UID EXPUNGE command
   or because messages were expunged in other connections also
   decrements the number of messages in the mailbox; it is not necessary
   for the server to send an EXISTS and/or RECENT response with the new
   value.  It also decrements message sequence numbers for each
   successive message in the mailbox (see the example at the end of this
   section).  Note that a VANISHED response caused by EXPUNGE/UID
   EXPUNGE/messages expunged in other connections SHOULD only contain
   UIDs for messages expunged since the last VANISHED/EXPUNGE response
   sent for the currently opened mailbox or since the mailbox was
   opened.  That is, servers SHOULD NOT send UIDs for previously
   expunged messages, unless explicitly requested to do so by the UID
   FETCH (REPORTEXPUNGES) command.



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   Note that client implementors must take care to properly decrement
   the number of messages in the mailbox even if a server violates this
   last SHOULD or repeats the same UID multiple times in the returned
   UID set.  In general this means that a client using this extension
   should either avoid using message numbers entirely, or have a
   complete map of UID-to-message mapping for the selected mailbox.

   A VANISHED response MUST NOT be sent when no command is in progress,
   nor while responding to a FETCH, STORE, or SEARCH command.  This rule
   is necessary to prevent a loss of synchronization of message sequence
   numbers between client and server.  A command is not "in progress"
   until the complete command has been received; in particular, a
   command is not "in progress" during the negotiation of command
   continuation.

   Note: UID FETCH, UID STORE, and UID SEARCH are different commands
   from FETCH, STORE, and SEARCH.  A VANISHED response MAY be sent
   during a UID command.  However, the VANISHED response MUST NOT be
   sent during a UID SEARCH command that contains message numbers in the
   search criteria.

   The update from the VANISHED response MUST be recorded by the client.

   Example: Let's assume that there is the following mapping between
   message numbers and UIDs in the currently selected mailbox (here "X"
   marks messages with the \Deleted flag set, and "x" represents UIDs
   which are not relevant for the example):

   Message numbers:   1    2    3    4    5  6   7  8  9 10  11
   UIDs:              x  504  505  507  508  x 510  x  x  x 625
   \Deleted messages:           X    X           X            X

   In the presence of the extension defined in this document:

   C: A202 EXPUNGE
   S: * VANISHED 505,507,510,625
   S: A202 OK EXPUNGE completed














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   Without the X-DRAFT-I02-EXPUNGED [[anchor15: change before
   publication]] extension the same example might look like:

   C: A202 EXPUNGE
   S: * 3 EXPUNGE
   S: * 3 EXPUNGE
   S: * 5 EXPUNGE
   S: * 8 EXPUNGE
   S: A202 OK EXPUNGE completed

   (Continuing previous example) If subsequently messages with UIDs 504
   and 508 got marked as \Deleted:

   C: A210 EXPUNGE
   S: * VANISHED 504,508
   S: A210 OK EXPUNGE completed

   I.e., the last VANISHED response only contains UIDs of messages
   expunged since the previous VANISHED response.


4.  Server implementation considerations

   This section describes a poor implementation and an example of a good
   implementation.

4.1.  Server implementations that don't store extra state

   Strictly speaking, a server implementation that doesn't remember
   modsequences associated with expunged messages can be considered
   compliant with this specification.  Such implementations return all
   expunged messages specified in the UID set of the UID FETCH
   (REPORTEXPUNGES) command every time, without paying attention to the
   specified CHANGEDSINCE modsequence.  Such implementations are
   discouraged, as they can end up returning VANISHED responses bigger
   than the result of a UID SEARCH command for the same UID set.

4.2.  Additional state required on the server

   When compared to the [CONDSTORE] extension, this extension requires
   servers to store additional state associated with expunged messages.
   Note that implementations are not required to store this state in
   persistent storage, however use of persistent storage is advisable.

   One possible way to correctly implement the extension described in
   this document would be to store a queue of <UID set, modsequence>
   pairs. <UID set> can be represented as a sequence of <min UID, max
   UID> pairs.



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   When messages are expunged, one or more entry is added to the queue
   tail.

   When the server receives a request to return expunged messages since
   a given modsequence, it will search the queue from the tail (i.e.
   going from the highest expunged modsequence to the lowest), until it
   sees the first record with a modsequence less than or equal to the
   given modsequence, or it reaches the head of the queue.

   Note that indefinitely storing information about expunged messages
   can cause storage and related problems for an implementation.  In the
   worst case, this could result in almost 64Gb of storage for each IMAP
   mailbox.  For example, consider an implementation that stores <min
   UID, max UID, modsequence> triples for each range of expunged
   messages expunged at once.  Each triple requires 16 octets: 4 octets
   for each of the two UIDs, and 8 octets for the modsequence.  Assume a
   mailbox containing a single message with a UID of 2**32-1 (the
   maximum possible UID value), where messages had previously existed
   with UIDs starting at 1, and have been expunged one at a time.  For
   this mailbox alone, storage is required for the triples <1, 1,
   modseq1>, <2, 2, modseq2>, ..., <2**32-2, 2**32-2, modseq4294967294>.

   Hence, implementations are encouraged to adopt strategies to protect
   against such storage problems, such as limiting the size of the queue
   used to store modsequences for expunged messages and "expiring" older
   records when this limit is reached.  When the selected
   implementation-specific queue limit is reached, the oldest record(s)
   are deleted from the queue (Note that such records are located at the
   queue head).  For all such "expired" records the server needs to
   store a single modsequence, which is the highest modsequence for all
   "expired" expunged messages.

   Also note that if the UIDVALIDITY of the mailbox changes or if the
   mailbox is deleted, then any state associated with expunged messages
   MUST be deleted as well.


5.  Updated synchronization sequence

   This section updates the description of optimized synchronization in
   section 6.1 of the [IMAP-DISC].

   An advanced disconnected mail client should use the X-DRAFT-I02-
   EXPUNGED and [CONDSTORE] extensions when they are supported by the
   server.  The client MUST cache the value from HIGHESTMODSEQ OK
   response code received on mailbox opening and update it whenever the
   server sends MODSEQ FETCH data items.




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   If the client receives a NOMODSEQ OK untagged response instead of
   HIGHESTMODSEQ, it MUST remove the last known HIGHESTMODSEQ value from
   its cache and follow the more general instructions in section 3 of
   the [IMAP-DISC].

   When the client opens the mailbox for synchronization it first
   compares UIDVALIDITY as described in step d)1) in section 3 of the
   [IMAP-DISC].  If the cached UIDVALIDITY value matches the one
   returned by the server, the client MUST compare the cached value of
   HIGHESTMODSEQ with the one returned by the server.  If the cached
   HIGHESTMODSEQ value also matches the one returned by the server, then
   the client SHOULD NOT fetch flags for cached messages, as they
   haven't changed.  If the value returned by the server is higher than
   the cached one, the client MAY use "SEARCH MODSEQ <cached-value>" to
   find all messages with flags changed since the last time the client
   was online and had the mailbox opened.  Alternatively the client MAY
   use "FETCH 1:* (FLAGS) (CHANGEDSINCE <cached-value> REPORTEXPUNGES)".
   The latter operation combines reporting expunged messages, searching
   for changed messages and fetching new information.

   In all cases the client still needs to fetch information about new
   messages (if requested by the user).  If the client has used SEARCH
   MODSEQ, it will also have to discover which messages have been
   expunged.

   Step d) ("Server-to-client synchronization") in section 4 of the
   [IMAP-DISC] in the presence of the X-DRAFT-I02-EXPUNGED & CONDSTORE
   extensions is amended as follows:

   d) "Server-to-client synchronization" -- for each mailbox that
   requires synchronization, do the following:

   1a)         Check the mailbox UIDVALIDITY (see section 4.1 of the
               [IMAP-DISC] for more details) with SELECT/EXAMINE/STATUS.
               If the UIDVALIDITY value returned by the server differs,
               the client MUST



               *           empty the local cache of that mailbox;

               *           "forget" the cached HIGHESTMODSEQ value for
                           the mailbox;

               *           remove any pending "actions" which refer to
                           UIDs in that mailbox.  Note, this doesn't
                           affect actions performed on client generated
                           fake UIDs (see section 5 of the [IMAP-DISC]);



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               *           skip steps 1b and 2-II;

   1b)         Check the mailbox HIGHESTMODSEQ.  If the cached value is
               the same as the one returned by the server, skip fetching
               message flags on step 2-II, i.e., the client only has to
               find out which messages got expunged.

   2)          Fetch the current "descriptors";

   I)          Discover new messages.

   II)         Discover changes to old messages and expunged messages
               using "UID FETCH 1:<lastseenuid> (FLAGS) (CHANGEDSINCE
               <cached-value> REPORTEXPUNGES)".

               (Note, if <lastseenuid> is replaced with "*", this
               command will return flags for new messages as well)

   3)          Fetch the bodies of any "interesting" messages that the
               client doesn't already have.

   Example:    The UIDVALIDITY value is the same, but the HIGHESTMODSEQ
               value has changed on the server while the client was
               offline:




    C: A142 SELECT INBOX
    S: * 172 EXISTS
    S: * 1 RECENT
    S: * OK [UNSEEN 12] Message 12 is first unseen
    S: * OK [UIDVALIDITY 3857529045] UIDs valid
    S: * OK [UIDNEXT 201] Predicted next UID
    S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
    S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
    S: * OK [HIGHESTMODSEQ 20010715194045007]
    S: A142 OK [READ-WRITE] SELECT completed













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               after that:

    C: A143 UID FETCH 1:20 (FLAGS)
        (CHANGEDSINCE 20010715194032001 REPORTEXPUNGES)
    S: * 2 FETCH (UID 6 MODSEQ (20010715205008000)
        FLAGS (\Deleted))
    S: * 5 FETCH (UID 9 MODSEQ (20010715195517000)
        FLAGS ($NoJunk $AutoJunk $MDNSent))
       ...
    S: * VANISHED 1:5,7:8,10:15
    S: A143 OK FETCH completed


6.  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], 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.

   capability         =/ "X-DRAFT-I02-EXPUNGED"
                         ;; [[Note to RFC Editor: fix before
                         ;; publication]]

   message-data       =/ expunged-resp

   expunged-resp      =  "VANISHED" [expunge-correlator] SP known-uids

   expunge-correlator =  SP "(" single-exp-correlator *(SP single-exp-
                         correlator) ")"
                         ;; Unless explicitly specified otherwise, ;;
                         all correlator types must be specified ;; only
                         once.

   single-exp-correlator =  "TAG" SP tag-string ;; Correlator type
                         followed by parameters

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






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   rexpunges-fetch-mod = "REPORTEXPUNGES"
                         ;; REPORTEXPUNGES FETCH modifier conforms
                         ;; to the fetch-modifier syntax
                         ;; defined in [IMAPABNF].  It is only
                         ;; allowed in the UID FETCH command.

   select-param =/       expunged-param
                         ;; conforms to the generic "select-param"
                         ;; non-terminal syntax defined in [IMAPABNF].

   expunged-param =      "REPORTEXPUNGES"


7.  Security Considerations

   It is believed that this extension doesn't raise any additional
   security concerns not already discussed in [RFC3501].

   As always, it is important to thoroughly test clients and servers
   implementing this extension, as it changes how the server reports
   expunged messages to the client.


8.  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-I02-EXPUNGED [[anchor23: Note to
   RFC Editor: change before publication]] IMAP capability.  IANA is
   requested to add it to the registry.


9.  Acknowledgments

   Thanks to Steve Hole, Cyrus Daboo, David Cridland and Michael Wener
   for encouraging me to write this document.

   Valuable comments, both in agreement and in dissent, were received
   from David Cridland, Timo Sirainen, Michael Wener, Randall Gellens,
   Arnt Gulbrandsen, Peter Coates, Mark Crispin and Elwyn Davies.

   This document takes substantial text from [RFC3501] by Mark Crispin.





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10.  References

10.1.  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.

   [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.

   [UIDPLUS]  Crispin, M., "Internet Message Access Protocol (IMAP) -
              UIDPLUS extension", RFC 4315, December 2005.

10.2.  Informative References

   [IMAP-DISC]
              Melnikov, A., "Synchronization Operations For Disconnected
              Imap4 Clients", RFC 4549, June 2006.


Author's Address

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

   Email: Alexey.Melnikov@isode.com









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Full Copyright Statement

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Acknowledgment

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   Administrative Support Activity (IASA).





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