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Versions: 00                                                            
IMAP Extensions Working Group                                 C. Daboo
Internet Draft: IMAP VIEW Extension                       M. Pustilnik
                                                            M. Crispin
Document: draft-ietf-imapext-view-00.txt                     July 2000

                          IMAP VIEW Extension

Status of this Memo

    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of RFC2026.  Internet-Drafts are
    working documents of the Internet Engineering Task Force (IETF), its
    areas, and its working groups.  Note that other groups may also
    distribute working documents as Internet-Drafts.

    Internet-Drafts are draft documents valid for a maximum of six
    months and may be updated, replaced, or obsoleted by other documents
    at any time.  It is inappropriate to use Internet-Drafts as
    reference material or to cite them other than as "work in progress."

    The list of current Internet-Drafts can be accessed at
    http://www.ietf.org/ietf/1id-abstracts.txt.  The list of Internet-
    Draft Shadow Directories can be accessed at
    http://www.ietf.org/shadow.html.


Copyright Notice

    Copyright (C) The Internet Society (2000). All Rights Reserved.




























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                           Table of Contents
     1  Abstract  . . . . . . . . . . . . . . . . . . . . . . . . . .  2
     2  Conventions Used in This Document  . . . . . . . . . . . . .   2
     3  Introduction and Overview . . . . . . . . . . . . . . . . . .  3
     4  Commands . . . . . . . . . . . . . . . . . . . . . . . . . .   4
       4.1  VIEW Command  . . . . . . . . . . . . . . . . . . . . . .  5
         4.1.1  VIEW SET . . . . . . . . . . . . . . . . . . . . . .   5
         4.1.2  VIEW <sub-command>  . . . . . . . . . . . . . . . . .  6
       4.2  Modified SELECT and EXAMINE commands . . . . . . . . . .   8
     5  Responses . . . . . . . . . . . . . . . . . . . . . . . . . .  8
       5.1  Response Conditions  . . . . . . . . . . . . . . . . . .   8
       5.2  Server Modes  . . . . . . . . . . . . . . . . . . . . . .  9
       5.3  New Message Arrival Processing . . . . . . . . . . . . .   9
       5.4  Examples of use of the \View Flag . . . . . . . . . . . . 10
         5.4.1  Dynamic  . . . . . . . . . . . . . . . . . . . . . .  10
         5.4.2  Semi-dynamic  . . . . . . . . . . . . . . . . . . . . 11
         5.4.3  Static . . . . . . . . . . . . . . . . . . . . . . .  11
       5.5  VIEW Untagged Response  . . . . . . . . . . . . . . . . . 12
         5.5.1  New message arrival  . . . . . . . . . . . . . . . .  12
         5.5.2  Messages moving in the view . . . . . . . . . . . . . 13
         5.5.3  VIEW SEARCH Response . . . . . . . . . . . . . . . .  14
       5.6  EXISTS Untagged Response  . . . . . . . . . . . . . . . . 15
       5.7  EXPUNGE Untagged Response  . . . . . . . . . . . . . . .  15
     6  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 16
     7  Security Considerations  . . . . . . . . . . . . . . . . . .  17
     8  References  . . . . . . . . . . . . . . . . . . . . . . . . . 17
     9  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .  18
    10  Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . 18

1 Abstract

    The VIEW extension to the Internet Message Access Protocol [IMAP4]
    permits a subset of messages in the mailbox to be processed
    separately from the entire set of messages in the mailbox.  This
    allows a client to restrict its view to only the messages appearing
    in this set.  The subset of messages also need not be returned in
    order of their sequence numbers, allowing clients to access messages
    in a particular sort order.

    The subsetting and sorting of messages is handled by existing
    [IMAP4] commands that return a set of messages as their result.
    This extension takes the set returned from such a command and
    applies the VIEW methodology to it.


2 Conventions Used in This Document

    The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD
    NOT", and "MAY" in this document are to be interpreted as described
    in "Key words for use in RFCs to Indicate Requirement Levels"
    [KEYWORDS].



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    Formal syntax is defined using ABNF [ABNF].

    In examples, "C:" and "S:" indicate lines sent by the client and
    server respectively.


3 Introduction and Overview

    The VIEW extension is present in any IMAP4 implementation which
    returns "VIEW" as one of the supported capabilities in the
    CAPABILITY command.

    The VIEW extension specifies one new command and introduces one new
    untagged response, modifies two existing [IMAP4] commands and two
    existing [IMAP4] untagged responses, as well as putting requirements
    on standard IMAP4 protocol responses when the command is in effect.
    It also introduces a new message flag.

    Each of the features in VIEW are optimizations; clients can provide
    the same functionality, albeit more slowly, by using existing
    commands.

    The design goal of the VIEW extension is to allow clients to
    reference messages only by their "view position numbers" as opposed
    to sequence numbers or UIDs, if so desired, and thus remove the need
    for the client to maintain its own mapping between sequence number,
    UID and view position.

    This extension makes the following changes to the IMAP4 protocol:

    (a) Adds a new VIEW command which takes one of two forms:

        (i) The first form, VIEW SET, takes an optional sub-command and
        is used to initiate or cancel the view mechanism on the server.

        (ii) In the second form, the VIEW command is used with a FETCH,
        COPY, STORE or SEARCH command, and instructs the server to
        interpret the sequence numbers provided by the client in the
        command as VIEW positions (as described below), or to return
        results using view positions rather than sequence numbers.  The
        VIEW COPY command also requires that messages be copied in view
        order into the destination mailbox.

    (b) Allows the arguments of the VIEW SET command to appear as
        arguments of the SELECT or EXAMINE commands [IMAP4] to allow
        selecting a mailbox and setting a view in a single round-trip.

    When the VIEW SET command is used by the client, the following
    changes also take place:

    (c) New FETCH message data response item:



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        VIEW
            Indicates the position of messages in the view, which may be
            different from message sequence number.

    (d) New untagged response:

        VIEW
            Indicates new message arrival, a change in position of a
            message within the current view or a message moving in or
            out of the current view.  The sequence number, UID and new
            view position number of the message are supplied, and
            optionally the old position when the message is not new.
            Can also be used to return SEARCH results using view
            position numbers rather than sequence numbers or UIDs.

    (e) Changes to untagged responses and response codes:

        EXISTS
            The standard EXISTS response is enhanced to include
            information about the total number of messages in the
            current view.

        EXPUNGE
            The standard EXPUNGE response is enhanced to include
            information about message UID and view position.

    (f) New message flag:

       \View
            The \View message flag is used to help clients create views
            that contain specific messages that it wants.  This allows
            clients to implement a 'static' or 'semi-dynamic' view (as
            described in the Section 5.2).  The \View flag is only
            present when a VIEW is in effect.  This flag is a 'session'
            flag.  Its state must be maintained by the server separately
            for each connection.

    (g) New search criteria:

       VIEW UNVIEW
            The VIEW search criterion matches any message that has the
            \View flag set.  The UNVIEW search criterion matches any
            message that does not have the \View flag set.  These search
            criteria are only present when a VIEW is in effect.


    The rest of this document describes these changes more rigorously.
    The document will use the IMAP4 SEARCH command as an example of a
    sub-command to VIEW SET.  However, other commands can be used with
    VIEW SET as well.




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4 Commands

4.1 VIEW Command

    The VIEW command takes one of two forms.

4.1.1 VIEW SET

    Arguments: OPTIONAL sub-command and associated arguments:
               this draft currently only allows the SEARCH command
               as the sub-command, however, anticipated SORT [SORT]
               and THREAD [THREAD] commands are expected to be
               added to this.

    Responses: REQUIRED untagged responses: modified EXISTS if
                                            sub-command present

    Result:    OK - view completed, now in view state
               NO - view failure
               BAD - command unknown or arguments invalid

    The VIEW SET command is only available when the server is in
    'selected state' [IMAP4].  Thus a successful SELECT or EXAMINE
    command MUST have been issued before VIEW SET can be used.  If a
    client attempts to use VIEW SET while the server is not in 'selected
    state', then the server MUST respond with a BAD response.  Note that
    a view can also be initiated by a SELECT or EXAMINE command, as
    described in Section 4.2.

    When the VIEW SET command is in effect (either by an explicit VIEW
    SET command or by a modified SELECT or EXAMINE command), it results
    in the following changes to the IMAP4 protocol:

    (a) The server creates a 'view' that is a subset of messages in the
        mailbox that match the results of the sub-command.  The position
        of a message in the view, its view position number, is then
        given by the VIEW fetch item response.  Messages outside of the
        view have a view position of 0 (zero).

    (b) The server MUST set the \View message flag on all messages
        appearing in the view and remove the \View message flag from all
        messages that are outside the view.  Note that the server MUST
        NOT send unsolicited FETCH responses to indicate the change in
        \View flag state of any messages.

    (c) The VIEW command can be used by the client to request
        information about messages in the current view set, without
        requiring the client to determine the view positions of every
        message in the mailbox (see Section 4.1.2).

    (d) The server MUST return a VIEW fetch item in every FETCH
        response, including unsolicited FETCH responses.  This ensures


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        the client does not need to maintain its own mapping from
        sequence numbers to view positions.

    (e) A new VIEW untagged response MUST be sent by the server when
        changes are made to the view by the arrival of new messages, the
        removal of messages, and the change in status of messages.  The
        rules governing when these responses are issued are described in
        more detail in Section 5.1.

    (f) The server MUST modify the EXISTS untagged response (see Section
        5.6) to include additional information to indicate the current
        number of messages in the view set.

    (g) The server MUST modify the EXPUNGE untagged response (see
        Section 5.7) to include additional information to indicate the
        expunged message's UID and view position number.

    (h) The VIEW SET command with no sub-command can be used to turn off
        the view facility and return the server to standard IMAP4
        behaviour.  The server MUST NOT send unsolicited FETCH responses
        to indicate removal of the \View flag for messages previously in
        the VIEW.  Once the view has been turned off, the \View flag is
        not available.

    (i) A VIEW SET command with a sub-command (see Section 4.1.2) can be
        used while another VIEW SET is in effect.  This results in the
        view being 'reset' to use the new VIEW SET parameters.  The
        server MUST set the \View message flag on all messages appearing
        in the new view and remove the \View message flag from all
        messages that are outside the new view.  Note that the server
        MUST NOT send unsolicited FETCH responses to indicate the change
        in \View flag state of any messages.

    (j) Any SELECT, EXAMINE or CLOSE command issued while a VIEW SET is
        in effect has the behaviour of canceling the current view and
        returns the server to standard [IMAP4] behaviour, unless the
        SELECT or EXAMINE commands include new VIEW SET arguments as
        described in Section 4.2.  The server MUST NOT send unsolicited
        FETCH responses to indicate any change of the \View flag.  If
        the view has been turned off, the \View flag is not available.

    Examples:
        C: A999 VIEW SET SEARCH FROM "Smith"
        S: * 23 EXISTS 5
        S: A999 OK VIEW SET completed


4.1.2 VIEW <sub-command>

    Arguments:  command name
                command arguments



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    Responses:  untagged responses: FETCH, VIEW SEARCH

    Result:     OK - VIEW command completed
                NO - VIEW command error
                BAD - command unknown or arguments invalid

    This version of the VIEW command is only available when the VIEW SET
    command is in effect.  Clients MUST NOT issue this version of the
    VIEW command when a VIEW SET is not in effect, and servers MUST
    respond with a tagged BAD response if it receives a VIEW command of
    this type when VIEW SET is not in effect.  This version of the VIEW
    command has two forms.

    In the first form, it takes as its arguments a COPY, FETCH, or STORE
    command [IMAP4] with arguments appropriate for the associated
    command.  However, the numbers in the message set argument are view
    position numbers instead of message sequence numbers.

    When the VIEW COPY form is used, the server MUST copy messages into
    the destination mailbox in the order they appear in the current
    view.  This may be different from the ordering of the view position
    numbers provided as the argument to the VIEW COPY command.

    In the second form, the VIEW command takes a SEARCH command with
    SEARCH command arguments [IMAP4].  The interpretation of the
    arguments is the same as with SEARCH [IMAP4]; however, the numbers
    returned in a VIEW SEARCH response (see Section 5.5.3) for a VIEW
    SEARCH command are view position numbers instead of message sequence
    numbers.  In addition, the search is carried out only on those
    messages in the current view set, so a view position of 0 (zero)
    MUST NOT be returned in the search results.

    Example:
        C: A999 VIEW SEARCH UNSEEN
        S: * VIEW SEARCH 1 2 4 6
        S: A999 OK VIEW SEARCH completed

    When a FETCH response [IMAP4] is returned by the server when the
    VIEW SET command is in effect, the number after the "*" in an
    untagged FETCH response is always a message sequence number, not a
    view position number, even for a response to any of the above VIEW
    commands.  However, server implementations MUST implicitly include
    the VIEW fetch item as part of any FETCH response caused by a VIEW
    command, regardless of whether a VIEW was specified as a message
    data item to any FETCH, as described in Section 4.1.1 (c).

    Example:
        C: A999 VIEW FETCH 1:3 FLAGS
        S: * 23 FETCH (FLAGS (\Seen) VIEW 2)
        S: * 24 FETCH (FLAGS (\Seen) VIEW 3)
        S: * 25 FETCH (FLAGS (\Seen) VIEW 1)
        S: A999 OK VIEW FETCH completed


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4.2 Modified SELECT and EXAMINE commands

    This extension modifies the syntax of the existing IMAP4 SELECT and
    EXAMINE commands as follows.

    Arguments:  mailbox name
                OPTIONAL view set arguments

    Response:   same as [IMAP4] except for modified EXISTS

    Result:     same as [IMAP4]

    The IMAP4 SELECT and EXAMINE commands are modified to include
    optional VIEW SET command arguments after the mailbox name.  This
    allows a client to select a mailbox and set a view in a single
    command.  The syntax for the optional arguments are the same as for
    the VIEW SET command arguments, and the behaviour following such a
    command is as described in Section 4.1.1.

    When the optional VIEW SET command arguments are present, the EXISTS
    response that is normally sent by the server as part of the SELECT
    or EXAMINE command response is modified to include the current
    number of messages in the view, as described in Section 4.1.1 (f).

    Examples:
        C: A142 SELECT INBOX SEARCH FROM "Smith"
        S: * 172 EXISTS 5
        S: * 1 RECENT
        S: * OK [UNSEEN 12] Message 12 is first unseen
        S: * OK [UIDVALIDITY 3857529045] UIDs valid
        S: * OK [UIDNEXT 4392] Predicted next UID
        S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
        S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
        S: A142 OK [READ-WRITE] SELECT with VIEW SET completed


5 Responses

5.1 Response Conditions

    There are a number of conditions that can give rise to changes in
    the state of a mailbox when a VIEW SET command is in effect:

    (a) New messages arriving in the mailbox that also match the current
        view criteria

    (b) New messages arriving in the mailbox that do not match the
        current view criteria

    (c) Messages removed from the mailbox (via EXPUNGE) that also match
        the current view criteria



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    (d) Messages removed from the mailbox (via EXPUNGE) that do not
        match the current view criteria

    (e) Messages that do not match the current view criteria, but whose
        state changes (e.g. a change in the message FLAGS) such that
        they now match the current view criteria

    (f) Messages that match the current view criteria, but whose state
        changes (e.g. a change in the message FLAGS) such that they no
        longer match the current view criteria

    (g) Messages that match the current view criteria, but whose state
        changes (e.g. a change in the message FLAGS) resulting in a
        change to their view position, whilst still matching the current
        view criteria

    When VIEW SET is in effect, a server MUST always send untagged
    responses for all the above response conditions to satisfy the
    dynamic view mode behaviour described next.

5.2 Server Modes

    There are three different modes that a view could operate in:
    dynamic, semi-dynamic or static.  Depending on the mode, the server
    response conditions described above, may or may not be sent, as
    determined by the following table:

    +--------------------+-------------+--------------+-------------+
    | Response condition |   Dynamic   | Semi-dynamic |   Static    |
    +====================|==========================================+
    |     (a) (b)        |     Yes     |     Yes      |     No      |
    +--------------------|-------------+--------------+-------------+
    |     (c) (d)        |     Yes     |     Yes      |     Yes     |
    +--------------------|-------------+--------------+-------------+
    |   (e) (f) (g)      |     Yes     |     No       |     No      |
    +--------------------+-------------+--------------+-------------+

    Clients may want to operate in any of these modes, whereas for
    simplicity, servers should only have to operate in one mode.
    Therefore there needs to be a way to 'simulate' client modes given a
    single server mode.

    This specification adopts the dynamic mode of operation for the
    server.  Thus the server sends view update responses for all the
    response conditions listed in Section 5.1.  To simulate semi-dynamic
    and static modes, a new message flag \View is introduced that allows
    messages to be marked as belonging to the current view.  This flag
    is automatically set by the server when a message is added to the
    view, but only the client can remove it.  Examples of the use of
    this flag in simulating different view modes are given Section
    5.4.



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5.3 New Message Arrival Processing

    A special case exists for processing of new messages arriving in a
    mailbox.  To determine whether new messages match the current view
    criteria the server must follow these rules:

    i) If the view criteria does not include any criterion for the \View
        flag, then the new message is considered to be in the view if it
        matches the view criteria.  If a new message is added to the
        view, the server MUST set the \View flag for that message, but
        MUST NOT send an unsolicited FETCH response to indicate the
        change in \View flag state.

    ii) If the view criteria contains any criterion for the \View flag,
        the following procedure must be followed: the server should test
        the message against the view criteria for the two cases where
        the \View flag is set and not set.  Based on the results of
        these tests, the message may be added to the view with the \View
        flag either set or not set:

    +--------------+--------------+----------------------------+
    | Test without | Test with    |           Result           |
    | \View        | \View        |----------------------------|
    |              |              | Add to VIEW  | \View flag  |
    +==========================================================+
    |              |              |              |             |
    |    false     |    false     |     No       |   Not set   |
    |              |              |              |             |
    +--------------+--------------+--------------+-------------+
    |              |              |              |             |
    |    false     |    true      |     Yes      |   Set       |
    |              |              |              |             |
    +--------------+--------------+--------------+-------------+
    |              |              |              |             |
    |    true      |    false     |     Yes      |   Not set   |
    |              |              |              |             |
    +--------------+--------------+--------------+-------------+
    |              |              |              |             |
    |    true      |    true      |     Yes      |   Set       |
    |              |              |              |             |
    +--------------+--------------+--------------+-------------+

5.4 Examples of use of the \View Flag

5.4.1 Dynamic

    A typical scenario is that the user wants to display only 'new'
    messages in a particular mailbox and read those messages.  A VIEW
    command to trigger this behaviour would be:

        C: A001 VIEW SET SEARCH UNSEEN



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    This generates a dynamic view that shows only unseen messages.  As
    soon as a message has the \Seen flag set, it drops out of the view.
    New messages arriving in the mailbox without the \Seen flag set are
    automatically added to the view.

    Another example is a view that 'hides' deleted messages
    automatically.  The VIEW command to trigger this would be:

        C: A001 VIEW SET SEARCH UNDELETED

    This generates a dynamic view containing only undeleted messages.
    As soon as a message in the view is deleted, it drops out of the
    view.

5.4.2 Semi-dynamic

    In the first dynamic example above, as soon as the user reads a
    message, it would drop out of the view as its \Seen flag would
    likely be set.  This can lead to undesired view updating in the
    client as the message the user is working with suddenly 'disappears'
    from their view.  A better solution is to use a semi-dynamic mode
    whereby the view shows initially unseen messages, but those messages
    remain in the view once they are marked as seen.  New messages
    arriving in the mailbox without the \Seen flag set, will be
    automatically added to the view.  The VIEW command to trigger this
    behaviour would be:

        C: A001 VIEW SET SEARCH OR UNSEEN VIEW

    By adding the VIEW search criteria, any messages initially appearing
    in the view will remain in the view because they have their \View
    flag set automatically.  Following the rules described in Section
    5.3, new messages arriving in the mailbox without the \Seen flag set
    would automatically be added to the view by the server, which would
    also set the \View flag on those messages.

    A client can 'refresh' the semi-dynamic view to remove messages that
    don't match the search criteria, other than having their \View flag
    set, by re-issuing the original view command.

    Clients may want to combine dynamic and semi-dynamic behaviours.
    For example, a semi-dynamic 'unseen messages only' view with a
    dynamic 'hide deleted messages' view.  This could be accomplished
    with the following VIEW command:

        C: A001 VIEW SET SEARCH (OR UNSEEN VIEW) UNDELETED

5.4.3 Static

    Clients can create static view using:

        C: A001 VIEW SET SEARCH VIEW


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    This creates a view that initially has no contents.  Clients can
    then manage the contents of the view by setting or removing the
    \View flag for messages in the mailbox.  Setting the \View flag will
    add a message to the view, removing the \View flag will remove a
    message from the view.  New messages are not automatically added to
    the view, but messages expunged from the mailbox will be removed
    from the view if they have their \View flag set.


5.5 VIEW Untagged Response

    The VIEW untagged response is used to inform the client of changes
    to the current view.  This includes new messages appearing in the
    view, messages being removed from the view, and messages changing
    position inside the view.

5.5.1 New message arrival

        <seq> VIEW <uid> <newpos>

        indicates that a new message has arrived with the given sequence
        number, UID and view position number

    When using the VIEW SET command, the VIEW untagged response augments
    the EXISTS untagged response as a means of new mail notification.
    Specifically it is used to tell the client where new messages appear
    in the current view.  The server MUST send an untagged VIEW response
    for every new message that arrives in the mailbox, after the
    corresponding untagged EXISTS response is sent to indicate this,
    when the VIEW SET command is in effect.

    When the VIEW SET command is in effect, and the view position number
    of a new message is non-zero (i.e. the new message appears in the
    current view), the untagged VIEW response causes the view position
    numbers of all subsequent messages in the mailbox's current view to
    be incremented.  This corresponds to response condition (a)
    described in Section 5.1.

    Example:

        C: NOOP
        S: * 173 EXISTS 24
        S: * 1 RECENT
        S: * 173 VIEW 5274234 14
        S: NOOP complete

        indicates that a new message with sequence number 173 and UID
        5274234 has been inserted into the view with view position
        number 14.  Any message that used to have a view position number
        14 is now at position 15, etc.




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    If a new message arrives outside the current view (i.e. not matching
    the specified search criteria), the view position number of the new
    message is given as 0.  This corresponds to response condition (b)
    described in Section 5.1.

    Example:

        C: NOOP
        S: * 174 EXISTS 24
        S: * 2 RECENT
        S: * 174 VIEW 5274235 0
        S: NOOP complete

        indicates that a message has arrived with sequence number 174
        and UID 5274235, however, the VIEW SET command in effect
        prevents it from being in the current view.


5.5.2 Messages moving in the view

        <seq> VIEW <uid> <new> <old>

        indicates that a message with the given sequence number and UID
        has changed its position within the view

    Some sub-commands of the VIEW SET command may change the sort order
    of messages in the view.  In such a case, changes to message flags
    or keywords can cause the position of messages in sorted order to
    change.  Also, when search criteria are specified, changes to
    message flags or keywords can cause messages to move into or outside
    of the view.  The server MUST communicate these changes to the
    client by sending it the VIEW untagged response

    When VIEW SET search criteria are in effect, changes made to a
    message can cause it to drop out of view or, on the contrary, become
    visible.  When a message drops out of view, the new view position
    number is sent as 0.  Similarly, when a message appears in view, for
    example, as a result of another agent changing the message
    attributes, the old view position number is sent as 0.

    When the old view position number in the VIEW untagged response is
    0, the effect of VIEW is a message inserted into the view at the
    position given by <new>.  The view position numbers of all
    subsequent messages in the current view are implicitly incremented.
    This corresponds to response condition (e) described in Section
    5.1.

    When the new view position number in the VIEW untagged response is
    0, the effect of VIEW is a message removed from the view at the
    position given by <old>.  The view position numbers of all
    subsequent messages in the current view are implicitly decremented.
    This corresponds to response condition (f) described in Section


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    5.1.

    When both the <old> and <new> view positions are non-zero, then the
    view positions of messages between the <old> and <new> positions
    need to be implicitly decremented or incremented depending on
    whether the <old> view position is less than or greater than the
    <new> view position, respectively.  This corresponds to response
    condition (g) described in Section 5.1.

    It is meaningless to have a VIEW untagged response where both <old>
    and <new> view position numbers are 0; the server MUST NOT generate
    VIEW responses of this form.

    VIEW untagged responses indicating messages moving in the view MUST
    NOT be sent as the result of messages being expunged (which is
    handled by the modified untagged EXPUNGE response), or when no
    command is in progress, or while responding to a FETCH, SEARCH or
    STORE command.  These rules are necessary to prevent loss of
    synchronization of message sequence numbers between client and
    server.

    Examples:

        S: * 172 VIEW 5274234 2 14

        indicates that the view position of the message with sequence
        number 172 and UID equal to 5274234 has changed from 14 to 2.
        The view position numbers of the messages in the range 2:13 are
        incremented.

        S: * 172 VIEW 5274234 0 14

        indicates that the message with view position number 14 has
        dropped out of view.  The view position numbers of subsequent
        messages are decremented.  The message continues to exist,
        however, it is outside of the current view and is therefore no
        longer accessible to the session via the VIEW command.

        S: * 173 VIEW 5274234 2 0

        indicates that the message with UID 5274234 has appeared in the
        current view and has been assigned view position number 2.  The
        view position numbers of subsequent messages are incremented.


5.5.3 VIEW SEARCH Response

        VIEW SEARCH <zero or more view position numbers>

    The VIEW SEARCH response occurs as a result of a VIEW SEARCH
    command.  The view position number(s) refer to those messages that
    match the search criteria.  Each number is delimited by a space.


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    Example:  S: * VIEW SEARCH 2 3 6


5.6 EXISTS Untagged Response

        <# in mailbox> EXISTS <# in view>

        indicates the total number of messages in the mailbox and in the
        current view

    The modified EXISTS untagged response MUST only be used when the
    VIEW SET command is in effect.  This MUST be sent in response to a
    VIEW SET command taking a sub-command argument.  Otherwise this
    response is sent under the same circumstances as the unmodified
    EXISTS response (i.e. in when there is a change to the total number
    of messages in the mailbox).

    Example:

        C: A142 SELECT INBOX
        S: * 172 EXISTS
        S: * 3 RECENT
        S: * OK [UNSEEN 12] Message 12 is first unseen
        S: * OK [UIDVALIDITY 3857429045] UIDs valid
        S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
        S: OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
        S: A142 OK [READ-WRITE] SELECT completed
        C: A143 VIEW SET SEARCH FROM "Smith"
        S: * 172 EXISTS 23
        S: A143 OK VIEW SET completed

    In this example, there are 172 messages in the mailbox and 23
    messages have a from address including the text "Smith".


5.7 EXPUNGE Untagged Response

        <seq> EXPUNGE <uid> <pos>

        indicates that a message with given sequence number, UID and
        view position number has been permanently removed from the
        mailbox

    When VIEW SET is in effect, the EXPUNGE untagged response [IMAP4] is
    modified to include the UID and view position number of the message
    being expunged.  The server MUST use this modified form of the
    EXPUNGE response whenever a VIEW SET command is in effect.

    When the view position number of the expunged message is non-zero,
    the modified EXPUNGE untagged response causes the view position
    numbers of all subsequent messages in the mailbox's current view to
    be decremented.  This corresponds to response condition (c)


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    described in Section 5.1.

    When search criteria are specified in the VIEW SET command, and a
    message outside the current view is expunged, the view position
    number of the expunged message is given as 0.  This corresponds to
    response condition (d) described in Section 5.1.

    Examples:

        S: * 172 EXPUNGE 5274234 14

        indicates that the message with sequence number 172, UID 5274234
        and view position number 14 has been expunged from its mailbox.
        Any message previously at position 15 is now at position 14, etc

        S: * 173 EXPUNGE 5274234 0

        indicates that a message with sequence number 173, UID 5274234
        was expunged, however, the message was outside the current view.

    A modified EXPUNGE untagged response MUST NOT be sent when no
    command is in progress; nor while responding to a FETCH, SEARCH or
    STORE command.  This rule is necessary to prevent loss of
    synchronization of message sequence numbers between client and
    server.


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
    [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.

    examine            = "EXAMINE" SP mailbox [SP view-set-arg]
                           ; redefines [IMAP4] EXAMINE command

    exists_resp        = number "EXISTS" SP number
                           ; replaces standard [IMAP4] EXISTS response
                           ; when VIEW SET is in effect

    expunge_resp       = nz-number "EXPUNGE" SP uniqueid SP position
                           ; replaces standard IMAP4 EXPUNGE response
                           ; when VIEW SET is in effect

    flag               =/ "\View"


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                           ; extends [IMAP4] message flags
                           ; new flag is only available when
                           ; VIEW SET is in effect

    msg-att-dynamic    =/ "VIEW" SP position
                           ; extends [IMAP4] message data item
                           ; FETCH response

    position           = number ["." number]
                           ; position number of messages in the view
                           ; may be hierarchical if sub-command defines
                           ; hierarchic ordering of messages
                           ; 0 means outside of the current view

    search-key         =/ "VIEW" / "UNVIEW"
                           ; extends [IMAP4] search criteria
                           ; new search criteria are only available
                           ; when a view is in effect

    select             = "SELECT" SP mailbox [SP view-set-arg]
                           ; redefines [IMAP4] SELECT command

    view               = "VIEW" SP (view-set / view-reference)

    view-mailbox-data  = "VIEW" SP (("SEARCH" *(SP position)) / OTHER)
                           ; OTHER reserved for future expansion

    view-msg-data      = nz_number SP "VIEW" SP uniqueid
                         SP position [SP position]

    view-reference     = copy / fetch / store / search
                           ; copy, fetch, store, search defined
                           ; in [IMAP4]

    view-response      = view-msg-data / view-mailbox-data

    view-set           = "SET" [SP view-set-arg]

    view-set-arg       = search / sort / thread / OTHER
                           ; search is defined in [IMAP4]
                           ; sort is defined in [SORT]
                           ; thread is defined in [THREAD]
                           ; OTHER reserved for future definition


7 Security Considerations

    There are no known security issues with this extension.


8 References



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    [ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications:
    ABNF", RFC 2234, Internet Mail Consortium, Demon Internet Ltd,
    November 1997.

    [KEYWORDS] Bradner, "Key words for use in RFCs to Indicate
    Requirement Levels", RFC 2119, Harvard University, March 1997.

    [IMAP4] Crispin, M., "Internet Message Access Protocol - Version
    4rev1", RFC 2060, University of Washington, December 1996.

    [MIME-IMB] Freed, N., and Borenstein, N.., "MIME (Multipurpose
    Internet Mail Extensions) Part One:  Format of Internet Message
    Bodies", RFC 2045, November 1996.

    [RFC-822] Crocker, D., "Standard for the Format of ARPA Internet
    Text Messages", STD 11, RFC822, August 1982.

    [SORT] Crispin, M., "Internet Message Access Protocol - SORT
    Extension", draft-ietf-imapext-sort-03.txt (Work in progress)

    [THREAD] Crispin, M., "Internet Message Access Protocol - THREAD
    Extension", draft-crispin-imapext-thread-01.txt (Work in progress)

9 Acknowledgments

    Steve Hole, Chris Newman and Larry Osterman have made significant
    contributions to the creation and refinement of the ideas expressed
    in this document.


10 Authors' Addresses

    Cyrus Daboo
    Cyrusoft International, Inc.
    Suite 780, 5001 Baum Blvd.
    Pittsburgh, PA 15213

    Phone: (412) 605-0499
    Email: daboo@cyrusoft.com


    Mark Pustilnik
    Microsoft
    1 Microsoft Way
    Redmond, WA 98052

    Phone: (425) 703-5758
    Email: markpu@microsoft.com

    Mark R. Crispin
    Networks and Distributed Computing
    University of Washington


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    4545 15th Avenue NE
    Seattle, WA 98105-4527

    Phone: (206) 543-5762
    EMail: MRC@CAC.Washington.EDU

















































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