Network Working Group                                        Curtis King
Internet-Draft                                    Alexey Melnikov
Internet-Draft                                                Isode Ltd.
Intended Status: Proposed Standard                            Isode Ltd.                      Arnt Gulbrandsen
                                                  Oryx Mail Systems GmbH
                                                       February 25,
                                                             Curtis King
                                                              Isode Ltd.
                                                          March 24, 2008

                       The IMAP NOTIFY Extension
                 draft-ietf-lemonade-imap-notify-04.txt
                 draft-ietf-lemonade-imap-notify-05.txt

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Copyright Notice

    Copyright (C) The IETF Trust (2008).

Abstract

    This document defines an IMAP extension which allows a client to
    request specific kinds of unsolicited notifications for specified
    mailboxes, such as messages being added to or deleted from
    mailboxes.

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    [[Add Updates: RFC-CONTEXT to the headers]]

1.  Conventions Used in This Document

    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].

    Formal syntax is defined by [RFC5234] as extended by [RFC3501] and
    [RFC4466].

    The acronym MSN stands for Message Sequence Numbers (see Section
    2.3.1.2 of [RFC3501]).

    Example lines prefaced by "C:" are sent by the client and ones
    prefaced by "S:" by the server. "[...]" means elision.

2.  Overview and rationale

    The IDLE command (defined in [RFC2177]) provides a way for the
    client to go into a mode where the IMAP server pushes notifications
    about IMAP mailstore events for the selected mailbox.  However, the
    IDLE extension doesn't restrict or control which server events can
    be sent, or what information the server sends in response to each
    event.  Also, IDLE only applies to the selected mailbox, thus
    requiring an additional TCP connection per mailbox.

    This document defines an IMAP extension that allows clients to
    express their preferences about unsolicited events generated by the
    server.  The extension allows clients to only receive events they
    are interested in, while servers know that they don't need to go
    into effort of generating certain types of untagged responses.

    Without the NOTIFY command defined in this document, and an IMAP server
    will only send information about mailstore changes to the client in
    the following cases:
      -  as the result of a client command (e.g. FETCH responses to
         a FETCH or STORE command),
      -  unsolicited responses sent just before the end of a command
         (e.g. EXISTS or EXPUNGE) as the result of changes in other
         sessions, and
      -  during an IDLE command.

    The NOTIFY command extends what information may be returned in those
    last two cases, and also permits and requires the server to send
    information about updates between command.  The NOTIFY command also

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    allows for the client to extend what information is sent unsolicited
    about the selected mailbox, and to request some update information
    to be sent regarding other mailboxes.

    For the new messages delivered to or appended to the selected
    mailbox, the NOTIFY command can be used to request that a set of
    attributes be sent to the client in an unsolicited FETCH response.
    This allows a client to be passive recipient of events and new mail,
    and be able to maintain full synchronisation without having to issue
    any subsequent commands except to modify the state of the mailbox on
    the server.

    Some mobile clients, however, may want mail "pushed" only for mail
    that matches a SEARCH pattern.  To meet that need [CONTEXT] is
    augmented by this document to extend the UPDATE return option to
    specify a list of fetch-atts to be returned when a new message is
    delivered or appended in another session.

   [[Should

    [[RFC-Editor: Please delete the following before publication:
    Comments regarding this draft may be a normative subsection?]] sent either to the
    lemonade@ietf.org mailing list or to the authors.]]

3.  The NOTIFY extension

IMAP servers which support this extension advertise the X-DRAFT-W04-NOTIFY
   extension. X-DRAFT-
    W05-NOTIFY capability.  This extension adds the NOTIFY command as
    defined in Section 5.1.

    A server implementing this extension is not required to implement
    LIST-EXTENDED [LISTEXT], even though a NOTIFY compliant server must
    be able to return extended LIST responses defined in [LISTEXT].

    [[RFC-Editor: Please delete the following before publication:
   Comments regarding this draft may Should QRESYNC be sent either to the
   lemonade@ietf.org mailing list or to the authors.]]

3. a required dependency for this
    extension?]]

3.1. The NOTIFY Command

    Arguments: "SET"
               optional STATUS indicator
               Mailboxes to be watched
               Events about which to notify the client
    Or
    Arguments: "NONE"

    Responses: Possibly untagged STATUS responses (for SET)

    Result: OK - The server will notify the client as requested.
            NO - Unsupported notify event, NOTIFY too complex or
               expensive, etc.
           BAD - Command unknown, invalid, unsupported or unknown

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               arguments.

    The NOTIFY command informs the server that the client listens for
    event notifications all the time (even when no command is in
    progress) and requests the server to notify it about the specified
    set of events. The NOTIFY command has two forms. NOTIFY NONE
    specifies that the client is not interested in any kind of event
    happening on the server. NOTIFY SET replaces the current list of
    interesting events with a new list of events.

    Until the NOTIFY command is used for the first time, the server only
    sends notifications while a command is being processed, and notifies
    the client about these events on the selected mailbox: (see section
    5 for definitions): MessageNew, MessageExpunge, FlagChange. It does
    not notify the client about any events on other mailboxes.

    The effect of a successful NOTIFY command lasts until the next
    NOTIFY command, or until the IMAP connection is closed.

    A successful NOTIFY SET command MUST cause the server to immediately
    return any accumulated changes to the currently selected mailbox (if
    any), such as flag changes, new or expunged messages. This is
    equivalent to NOOP command being issued by the client just before
    the NOTIFY SET command.

    The NOTIFY SET command can request notifications of changes to the
    selected mailbox, whatever it may be at the time the notifications
    are being generated. This is done by specifying the SELECTED mailbox
    selector (see Section 6.1) in the NOTIFY SET command.  The client
    can also request notifications on other mailboxes by name or by a
    limited mailbox pattern match.  The notifications returned for the
    currently selected mailbox will be those specified by the SELECTED
    mailbox specifier, even if the selected mailbox also appears by name
    in the command.

    If the NOTIFY command enables MessageNew, MessageExpunge,
    AnnotationChange or FlagChange notification for a mailbox, mailbox other than
    SELECTED, and the client has specified the STATUS indicator
    parameter, then the server MUST send a STATUS response for that
    mailbox before NOTIFY's tagged OK. If MessageNew is enabled, the
    STATUS response MUST contain MESSAGES, UIDNEXT and UIDVALIDITY. If
    MessageExpunge is enabled, the STATUS response MUST contain
    MESSAGES. If either AnnotationChange or FlagChange are included, included and
    the server also supports CONDSTORE [RFC4551] and/or QRESYNC
    [QRESYNC] extension, the STATUS response MUST contain UIDVALIDITY
    and HIGHESTMODSEQ.  Absence of the STATUS indicator parameter allows
    the client to avoid the additional STATUS responses. This might be
    useful if the client has already retrieved this information before
    issuing the NOTIFY command.

    Clients are advised to limit the number of mailboxes used with
    NOTIFY. Particularly, if a client asks for events for all accessible
    mailboxes, the server may swamp the client with updates about shared
    mailboxes. This wastes both server and network resources.        For
    each mailbox specified, the server verifies that the client has
    access using the following test:

    - If the name does not refer to an existing mailbox, the server MUST
      ignore it.

    - If the name refers to a mailbox which the client can't LIST, the

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      server MUST ignore it. For a server that implements [RFC4314] this
      means that if the client that doesn't have the 'l' (lookup) right
      for the name, then the server MUST ignore the mailbox. This
      behavior prevents dislosure on potentially confidential
      information to clients which don't have rights to know it.

    - If the name refers to a mailbox which the client can LIST (e.g. it
      has the 'l' right from [RFC4314]), but misses doesn't have another right
      required for processing of the specified event(s), then the server
      MUST respond with an untagged extended LIST response containing
      the \NoAccess name attribute.  [[Alexey: Note, the newly defined
     \NoAccess doesn't mean that the client doesn't have any rights
     other than 'l'. The \NoAccess is only meaningful in the context of
     the specified NOTIFY command.]]

    The server SHOULD return the tagged OK response if the client has
    access to at least one of the mailboxes specified in the current
    list of interesting events.  The server MAY return the tagged NO
    response if the client has no access to any of the specified
    mailboxes and no access can ever be granted in the future (e.g. the
    client specified an event for 'Subtree Bar/Foo', 'Bar/Foo' doesn't
    exist and LIST returns \Noinferiors for the parent 'Bar').

    If the notification would be prohibitively expensive for the server
    (e.g. "notify me of all flag changes in all mailboxes"), the server
    MAY refuse the command with a tagged NO [NOTIFICATIONOVERFLOW]
    response.

    If the client requests information for events of an unsupported
    type, the server MUST refuse the command with a tagged NO response
    (not a BAD).  This response SHOULD contain the BADEVENT response
    code, which MUST list names of all events supported by the server.

    Here's an example:

         S: * OK [CAPABILITY IMAP4REV1 NOTIFY]
         C: a login bob alice
         S: a OK Password matched
         C: b notify set status (selected MessageNew (uid
            body.peek[header.fields (from to subject)]) MessageExpunge)
            (subtree Lists MessageNew)
         S: * STATUS Lists/Lemonade (UIDVALIDITY 4 UIDNEXT 9999 MESSAGES
            500)
         S: [...]
         S: * STATUS Lists/Im2000 (UIDVALIDITY 901 UIDNEXT 1 MESSAGES 0)
         S: b OK done
         C: c select inbox
         S: [...] (the usual 7-8 responses to SELECT)

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         S: c OK INBOX selected
                (Time passes. A new message is delivered to mailbox
                 Lists/Lemonade.)
         S: * STATUS Lists/Lemonade (UIDVALIDITY 4 UIDNEXT 10000
            MESSAGES 501)
                (Time passes. A new message is delivered to inbox.)
         S: * 127 FETCH (UID 127001 BODY[HEADER.FIELDS (From To
            Subject)] {75}
         S: Subject: Re: good morning
         S: From: alice@example.org
         S: To: bob@example.org
         S:
         S: )
                (Time passes. The client decides it wants to know about
                 one more mailbox.) mailbox.  As the client already knows
                 necessary STATUS information for all mailboxes below
                 the Lists mailbox and because "notify set status" would
                 cause STATUS responses for *all* mailboxes specified in
                 the NOTIFY command, including the ones for which the
                 client already knows STATUS information, the client
                 issues explicit STATUS request for the mailbox to be
                 added to the watch list, followed by the NOTIFY SET
                 without the STATUS parameter.)
         C: d STATUS misc (UIDVALIDITY UIDNEXT MESSAGES)
         S: * STATUS misc (UIDVALIDITY 1 UIDNEXT 999)
         S: d STATUS completed
         C: e notify set status (selected MessageNew (uid
            body.peek[header.fields (from to subject)]) MessageExpunge)
            (subtree Lists MessageNew) (mailboxes misc MessageNew)
         S: * STATUS misc (UIDVALIDITY 1 UIDNEXT 999)
               (This command enables notification on one mailbox and
                otherwise changes nothing, so one STATUS response is
                sent.[[AM: This is no longer correct.]])
        S: d e OK done

4.  Interaction with the IDLE Command

    If IDLE (as well as this extension) is supported, while processing
    IDLE the server MUST send the same events as instructed by the
    client using the NOTIFY command.

    NOTIFY makes IDLE unnecessary for some clients. If a client does not
    use MSNs and '*' in commands, it can request MessageExpunge and
    MessageNew for the selected mailbox using the NOTIFY command instead
    of entering the IDLE mode.

5.  Event Types

    Only some of the events in [MSGEVENT] can be expressed in IMAP, and
    for some of them there are several possible ways to express the
    event.

    This section specifies the events which an IMAP server can notify an
    IMAP client, and how.

    The server SHOULD omit notifying the client if the event is caused
    by this client. For example, if the client issues CREATE and has

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    requested MailboxName event that would cover the newly created
    mailbox, the server SHOULD NOT notify the client of the MailboxName
    change.

    All event types described in this document require the 'l' and 'r'
    rights (see [RFC4314]) on all observed mailboxes.  Servers that
    don't implement [RFC4314] should map the above rights to their
    access control model.

   Note that

    If FlagChange event is specified, MessageNew and MessageExpunge must MUST
    also be specified together.
   It by the client.  Otherwise the server MUST respond
    with the tagged BAD response.

    If one of MessageNew or MessageExpunge is not possible to specify one, but not specified, the other. both events
    MUST be specified.  Otherwise the server MUST respond with the
    tagged BAD response.

    If the client instructs the server not to send MessageNew and
    MessageExpunge for the selected mailbox, the server MUST still send
    EXISTS and EXPUNGE responses as required by IMAP (see [RFC3501]
    section 7). In other words, MessageExpunge instructs the server to
    notify the client immediately, and the lack of MessageExpunge
    instructs the server to notify the client during execution of the
    next command as specified in [RFC3501].  MessageNew is handled
    similarly by the server.

5.1. FlagChange and AnnotationChange

    If the flag/annotation flag and/or message annotation change happens in the selected
    mailbox, the server MUST notify the client by sending an unsolicited
    FETCH response, which MUST include UID and FLAGS/ANNOTATION FETCH
    data items. It MAY also send new FLAGS and/or OK [PERMANENTFLAGS
    ...] responses.

    If a search context is in effect as specified in [CONTEXT], an
    ESEARCH ADDTO or ESEARCH REMOVEFROM will also be generated, if
    appropriate.  [[Alexey: I don't think this is needed:  In this case, the FETCH response MUST precede the
    ESEARCH response.]] response.

    If the change happens in another mailbox, then the response depends
    on whether CONDSTORE [RFC4551] and/or QRESYNC [QRESYNC] is being
    used. If so, the server sends a STATUS (HIGHESTMODSEQ) response.
    Note that whenever mailbox UIDVALIDITY changes, the server MUST also
    include UIDVALIDITY in the STATUS response.  If CONDSTORE the number of
    messages with \Seen flag changes, the server MAY also include the
    UNSEEN in the STATUS response.  If CONDSTORE/QRESYNC is not used, used and
    the server choses not to include the UNSEEN, the server does not
    notify the client.  [[Open Issue: should there be a way to require
    the server to return UNSEEN?]]

    FlagChange covers the MessageRead, MessageTrash, FlagsSet and
    FlagsClear events in [MSGEVENT].

   [[Open Issue: Filip Navara requested for STATUS (UNSEEN) to be sent
   for MessageRead. Arnt considers that unsound, since it involves
   processing all messages in a mailbox after an event affecting only

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   one message, and since it's not reliable anyway.]]

    Example in the selected mailbox:
        S: * 99 FETCH (UID 9999 FLAGS ($Junk))

    And in another, with CONDSTORE in use:
        S: * STATUS Lists/Lemonade (HIGHESTMODSEQ 65666665)

5.2. MessageNew

    This covers both MessageNew and MessageAppend in [MSGEVENT].

    If the new/appended message is in the selected mailbox, the server
    notifies the client by sending an unsolicited EXISTS response,
    followed by an unsolicited FETCH response containing the information
    requested by the client. A FETCH response SHOULD NOT be generated
    for a new message created by the client on this particular
    connection, for instance as the result of an APPEND or COPY command
    to the selected mailbox performed by the client itself. The server
    MAY also send a RECENT response, if the server marks the message as
    \Recent.

    Note that a single EXISTS response can be returned for multiple
    MessageAppend/MessageNew events.

    If a search context is in effect as specified in [CONTEXT], an
    ESEARCH ADDTO will also be generated, if appropriate. In this case,
    the EXISTS response MUST precede the ESEARCH response.  Both the
    NOTIFY command and the SEARCH and SORT commands (see Section 7) can
    specify attributes to be returned for new messages.  These
    attributes SHOULD be combined into a single FETCH response.  The
    server SHOULD avoid sending duplicate data.  The FETCH response(s)
    MUST follow any ESEARCH ADDTO responses.

    If the new/appended message is in another mailbox, the server sends
    an unsolicited STATUS (UIDNEXT MESSAGES) response for the relevant
    mailbox. If CONDSTORE (defined in [RFC4551]) is in use, the
    HIGHESTMODSEQ status data item MUST be included in the STATUS
    response.

    The client SHOULD NOT use FETCH attributes that implicitly set the
    \seen flag, or that presuppose the existence of a given bodypart.
    UID, MODSEQ, FLAGS, ENVELOPE, BODY.PEEK[HEADER.FIELDS... and
    BODY/BODYSTRUCTURE may be the most useful attributes.

    Note that if a client asks to be notified of MessageNew events, the
    number of messages can increase at any time, and therefore the
    client cannot refer to a specific message using the MSN/UID '*'.

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    Example in the selected mailbox:
        S: * 444 EXISTS
        S: * 444 FETCH (UID 9999)

    And in another, without CONDSTORE:
        S: * STATUS Lists/Lemonade (UIDNEXT 10002 MESSAGES 503)

5.3. MessageExpunge

    If the expunged message(s) is/are in the selected mailbox, the
    server notifies the client using EXPUNGE (or VANISHED, if [QRESYNC]
    is being
   used). supported by the server and enabled by the client).

    If a search context is in effect as specified in [CONTEXT], an
    ESEARCH REMOVEFROM will also be generated, if appropriate.

    If the expunged message(s) is/are in another mailbox, the server
    sends an unsolicited STATUS (UIDNEXT MESSAGES) response for the
    relevant mailbox. If CONDSTORE is being used, HIGHESTMODSEQ MUST be
    included in the STATUS response.

    Note that if a client requests MessageExpunge, the meaning of a MSN
    can change at any time, so the client cannot use MSNs in commands
    anymore.  For example, such a client cannot use FETCH, but it has to
    use UID FETCH. The meaning of '*' can also change when messages are
    added or expunged. A client wishing to keep using MSNs MUST NOT
    request the MessageExpunge event.

    The MessageExpunge notification covers both MessageExpunge and
    MessageExpire events from [MSGEVENT].

    Example in the selected mailbox, without QRESYNC:
        S: * 444 EXPUNGE
    The same example in the selected mailbox, with QRESYNC:
        S: * VANISHED 5444
    And in another:
        S: * STATUS misc (UIDNEXT 999 MESSAGES 554)

5.4. MailboxName

    These notifications are sent if an affected mailbox name was created
    (with CREATE), deleted (with DELETE) or renamed (with RENAME).  For
    a server that implements [RFC4314] granting or revocation of the 'l'
    right to the current user on the affected mailbox MUST be considered
    mailbox creation/deletion respectively.  If a mailbox is created or
    deleted, the mailbox itself and its parent are considered to be
    affected.

    The server notifies the client by sending an unsolicited LIST

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    response for each affected mailbox name. If If, after the event, the
    mailbox name does not refer to a mailbox after accessible to the event, client,
    the \Nonexistent flag MUST be included.

    For each selectable [[Alexey: is "selectable" important?]] LISTable mailbox renamed, the server sends an extended LIST
    response [LISTEXT] for the new mailbox name, containing the OLDNAME
    extended data item with the old mailbox name.  When a mailbox is
    renamed, its children are renamed too.  No additional MailboxName
    events are sent for children in this case.  When INBOX is renamed, a
    new INBOX is assumed to be created.  No MailboxName event must be
    sent for INBOX in this case.

    Example of a newly created mailbox: mailbox (or granting of the 'l' right on
    the mailbox):

        S: * LIST () "/" "NewMailbox"

    And a deleted mailbox: mailbox (or revocation of the 'l' right on the
           mailbox):
        S: * LIST (\NonExistent) "/" "." "INBOX.DeletedMailbox"

    Example of a renamed mailbox:
        S: * LIST () "/" "NewMailbox" ("OLDNAME" ("OldMailbox"))

5.5. SubscriptionChange

    The server notifies the client by sending an unsolicited LIST
    responses for each affected mailbox name. If and only if the mailbox
    is subscribed after the event, the \Subscribed attribute (see
    [LISTEXT]) is included.

    Example:
        S: * LIST (\Subscribed) "/" "SubscribedMailbox"

5.6. MailboxMetadataChange

    The server sends an unsolicited LIST response including METADATA (as
    per Section 4.3.1 of [METADATA]). If possible, only the changed
    metadata should be included, but if necessary, all metadata must be
    included.

    Example:
        S: * LIST "/" "INBOX" (METADATA (/comment))

5.7. ServerMetadataChange

    The server sends an unsolicited METADATA response (as per Section
    4.5.2 of [METADATA]). Only the names of changed metadata entries

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    SHOULD be returned in such METADATA responses.

    Example:
        S: * METADATA (/comment)

5.8. Notification Overflow

    If the server is unable or unwilling to deliver as many
    notifications as it is being asked to, it may disable notifications
    for some or all clients.  It MUST notify these clients by sending an
    untagged "OK [NOTIFICATIONOVERFLOW]" response and behave as if a
    NOTIFY NONE command had just been received.

    Example:
        S: * OK [NOTIFICATIONOVERFLOW] ...A comment can go here...

5.9. ACL Changes

    Even if NOTIFY succeeds, it is still possible to loose lose access to the
    mailboxes monitoried at a later time. If this happens, the server
    MUST silently stop monitoring these mailboxes. If access is later granted,
    the server MUST restart event monitoring.

    The server SHOULD return the LIST response with the \NoAccess name
    attribute if and when the mailbox loses the 'l' right.  Simalarly,
    the server SHOULD return the LIST response with no \NoAccess name
    attribute, if the mailbox was previously reported as having
    \NoAccess, and later on the 'l' right is granted.

6.  Mailbox Specification

    Mailboxes to be monitored can be specified in several different
    ways.

    Only 'selected' (section 6.1) matches the currently selected
    mailbox.  All other mailbox specifications affect other (non-
    selected) mailboxes.

    If for any given event type the client specifies monitoring of the
    same mailbox several times, times (using the same or different mailbox
    specifications), the first specification wins. A common

    Note that for different event types different <event-group>s can
    apply to the same mailbox.  The following example is asking demonstrates this.
    In this example, MessageNew and MessageExpunge events are reported
    for INBOX due to the first <event-group>. SubscriptionChange event
    will also be reported for INBOX due to the second <event-group>.

        C: a notify set (mailboxes INBOX (Messagenew messageExpunge))
           (personal (SubscriptionChange))

    A typical client that supports the NOTIFY extension would ask for
    events on the selected mailbox and some named mailboxes.

    In this example, the client asks for MessageExpunge FlagChange events for all
    personal mailboxes except the selected mailbox:
        C: a notify set (selected (MessageNew (Messagenew (uid flags) flagchange))
           messageExpunge)) (personal (MessageNew FlagChange
           MessageExpunge))

6.1. Selected

    Selected refers to the mailbox selected using either SELECT or
    EXAMINE (see [RFC3501] section 6.3.1 and 6.3.2). When the IMAP
    connection is not in selected state, selected does not refer to any

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    mailbox.

6.2. Personal

    Personal refers to all selectable mailboxes in the user's personal
    namespace(s).

6.3. Inboxes

    Inboxes refers to all selectable mailboxes in the user's personal
    namespace(s) to which messages may be delivered by an MDA (see
    [EMAIL-ARCH], particularly section 4.3.3).

    If the IMAP server cannot easily compute this set, it MUST treat
    "inboxes" as equivalent to "personal".

6.4 Subscribed

    Subscribed refers to all mailboxes subscribed by the user.

    If the subscription list changes, the server MUST reevaluate the
    list.

6.5 Subtree

    Subtree is followed by a mailbox name or list of mailbox names.  A
    subtree refers to all selectable mailboxes which are subordinate to
    the specified mailbox plus the mailbox itself.

6.6 Mailboxes

    Mailboxes is followed by a mailbox name or a list of mailbox names.

    The server MUST NOT do wildcard expansion.  This means there is no
    special treatment for the LIST wildcard characters ('*' and '%') if
    they are present in mailbox names.

7.  Extension to SEARCH and SORT commands

    If the server that support the NOTIFY extension also supports
    CONTEXT=SEARCH and/or CONTEXT=SORT as defined in [CONTEXT], the
    UPDATE return option is extended so that a client can request that
    FETCH attributes be returned when a new message is added to the

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    context result set.

    For example:
        C: a00 SEARCH RETURN (COUNT UPDATE (UID BODY[HEADER.FIELDS (TO
           FROM
               SUBJECT)])) FROM "boss" S: * ESEARCH (TAG "a00") (COUNT
           17) S: a00 OK [...a new message is delivered...]  S: * EXISTS
           93 S: * ESEARCH (TAG "a00") ADDTO (0 93) S: * 93 FETCH (UID 127001 BODY[HEADER.FIELDS (FROM TO
           SUBJECT)] {76} S: Subject: Re: good morning S: From:
           myboss@example.org S: To: bob@example.org S: S: ) S: *
           ESEARCH (TAG "a00") ADDTO (0 93)

    Note that the EXISTS response MUST precede the ESEARCH response, and
   the any FETCH response responses, and
    together they MUST follow precede the ESEARCH response.

    No untagged FETCH response SHOULD be returned if a message becomes a
    member of UPDATE SEARCH due to flag or annotation changes.

8.  Formal Syntax

    The following syntax specification uses the Augmented Backus-Naur
    Form (ABNF) notation as specified in [RFC5234]. [RFC3501] defines
    the non-terminals "capability", "command-auth", "mailbox", "mailbox-
    data", "resp-text-code" and "search-key". The "modifier-update" non-
    terminal is defined in [CONTEXT]. "mbx-list-oflag" is defined in
    [RFC3501] and updated by [LISTEXT].

    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-W03-NOTIFY" "X-DRAFT-W05-NOTIFY"
                        ;; [[Note to RFC Editor: change the capability
                        ;; name before publication]]
        command-auth    =/ notify

        notify          = "NOTIFY" SP
                        (notify-set / notify-none)

        notify-set      = "SET" [status-indicator] SP event-groups
                        ; Replace registered notification events
                        ; with the specified list of events [[Alexey:
                       what about "most specific" event overriding a
                       pattern?]]

        notify-none     = "NONE"

Internet-draft                                             February 2008
                        ; Cancel all registered notification
                        ; events. The client is not interested
                        ; in receiving any events.

        status-indicator = SP "STATUS"

        one-or-more-mailbox = mailbox / many-mailboxes

        many-mailboxes = "(" mailbox *(SP mailbox) ")"

        event-groups    = event-group *(SP event-group)

        event-group     = "(" filter-mailboxes SP events ")"

        filter-mailboxes = "selected" / "inboxes" / "personal" /
                        "subscribed" /
                        ( "subtree" SP one-or-more-mailbox ) /
                        ( "mailboxes" SP one-or-more-mailbox )

        events          = ( "(" event *(SP event) ")" ) / "NONE"
                        ;; As in [MSGEVENT].
                        ;; "NONE" means that the client does not wish
                        ;; to receive any events for the specified
                        ;; mailboxes.

        event           = message-event
                        / mailbox-event / user-event / event-ext

        message-match-criteria = "(" search-key ")"

        message-event   = ( "MessageNew" [SP
                            "(" fetch-att *(SP fetch-att) ")" ] )
                       SP
                        / "MessageExpunge"
                        / "FlagChange" SP message-match-criteria
                        / "AnnotationChange" SP message-match-criteria
                        ;; "MessageNew" includes "MessageAppend" from
                        ;; [MSGEVENT]. "FlagChange" is any of
                        ;; "MessageRead", "MessageTrash", "FlagsSet",
                        ;; "FlagsClear" [MSGEVENT]. "MessageExpunge"
                        ;; includes "MessageExpire" [MSGEVENT].
                        ;; MessageNew and MessageExpunge MUST always
                        ;; be specified together. If FlagChange is
                        ;; specified, then MessageNew and MessageExpunge
                        ;; MUST be specified as well.
                        ;; The fett-att list may only be present for the
                        ;; SELECTED mailbox filter (<filter-mailboxes>).

        mailbox-event   = "MailboxName" /
                        "SubscriptionChange" / "MailboxMetadataChange"
                        ; "SubscriptionChange" includes
                        ; MailboxSubscribe and MailboxUnSubscribe.
                        ; "MailboxName" includes MailboxCreate,
                        ; "MailboxDelete" and "MailboxRename".

Internet-draft                                             February 2008

        user-event      = "ServerMetadataChange"

        event-ext       = atom
                        ;; For future extensions

        oldname-extended-item =  "OLDNAME" SP "(" mailbox ")"
                        ;; Extended data item (mbox-list-extended-item)
                        ;; returned in a LIST response when a mailbox is
                        ;; renamed.
                        ;; Note 1: the OLDNAME tag can be returned
                        ;; with and without surrounding quotes, as per
                        ;; mbox-list-extended-item-tag production.

        resp-text-code  =/ "NOTIFICATIONOVERFLOW" /
                        unsupported-events-code

        message-event-name   = "MessageNew" /
                        / "MessageExpunge" / "FlagChange" /
                        "AnnotationChange"

        event-name = message-event-name / mailbox-event /
                        user-event

        unsupported-events-code = "BADEVENT"
                        SP "(" event-name *(SP event-name) ")"

        modifier-update = "UPDATE"
                        [ "(" fetch-att *(SP fetch-att) ")" ]

        mbx-list-oflag =/ "\NoAccess"

9.  Security considerations

    It is very easy for a client to deny itself service using NOTIFY:
    Asking for all events on all mailboxes may work on a small server,
    but with a big server can swamp the client's network connection or
    processing capability. In the worst case, the server's processing
    could also degrade the service it offers to other clients.

    Server authors should be aware that if a client issues requests and
    does not listen to the resulting responses, the TCP window can
    easily fill up, and a careless server might block. This problem
    exists in plain IMAP, however this extension magnifies the problem.

    This extensions makes it possible to retrieve messages immediately
    when they are added to the mailbox. This makes it wholly impractical
    to delete sensitive messages using programs like imapfilter. Using
    [SIEVE] or similar is much better.

Internet-draft                                             February 2008

10.  IANA considerations

    The IANA is requested to add NOTIFY to the list of IMAP extensions,
    http://www.iana.org/assignments/imap4-capabilities.

    10.1.  Initial LIST-EXTENDED extended data item registrations

    It is requested that the following entry be added to the LIST-
    EXTENDED extended data item registry [LISTEXT]:

    To: iana@iana.org Subject: Registration of OLDNAME LIST-EXTENDED
    extended data item

    LIST-EXTENDED extended data item tag: OLDNAME

    LIST-EXTENDED extended data item description: The OLDNAME extended
    data item describes the old mailbox name for the mailbox identified
    by the LIST response.

    Which LIST-EXTENDED option(s) (and their types) causes this extended
    data item to be returned (if any): none

    Published specification : RFC XXXX, Section 5.4.

    Security considerations: none

    Intended usage: COMMON

    Person and email address to contact for further information:

      Alexey Melnikov <Alexey.Melnikov@isode.com>

    Owner/Change controller: iesg@ietf.org

11. Acknowedgements

    The authors gratefully acknowledge the help of Peter Coates, Dave
    Cridland, Mark Crispin, Cyrus Daboo, Abhijit Menon-Sen Menon-Sen, Timo
    Sirainen and Eric Burger.  In particular, Peter Coates contributed
    lots of text and useful suggestions to this document.

    Various examples are copied from other RFCs.

    This document builds on one published and two unpublished drafts by
    the same authors.

12. Normative References

Internet-draft                                             February 2008

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

    [RFC2177]  Leiba, "IMAP4 IDLE Command", RFC 2177, IBM, June 1997.

    [RFC3501]  Crispin, "Internet Message Access Protocol - Version
               4rev1", RFC 3501, University of Washington, June 2003.

    [RFC5234]  Crocker, Overell, "Augmented BNF for Syntax
               Specifications: ABNF", RFC 5234, Brandenburg
               Internetworking, THUS plc, January 2008.

    [RFC4314]  Melnikov, "IMAP4 Access Control List (ACL) Extension",
               RFC 4314, December 2005.

    [RFC4466]  Melnikov, Daboo, "Collected Extensions to IMAP4 ABNF",
               RFC 4466, Isode Ltd., April 2006.

    [RFC4551]  Melnikov, Hole, "IMAP Extension for Conditional STORE
               Operation or Quick Flag Changes Resynchronization", RFC
               4551, Isode Ltd., June 2006.

    [LISTEXT]  Leiba, Melnikov, "IMAP4 List Command Extensions", draft-
               ietf-imapext-list-extensions-18 (work in progress), IBM,
               September 2006.

    [METADATA] Daboo, "IMAP METADATA Extension", draft-daboo-imap-
               annotatemore-12 (work in progress), Apple Computer, Inc.,
               December 2007.

    [MSGEVENT] Newman, C. and R. Gellens, "Internet Message Store
               Events", draft-ietf-lemonade-msgevent-05.txt (work in
               progress), Sun, January 2008.

    [CONTEXT] Cridland, D. and C. King, "Contexts for IMAP4", work in
               progress, draft-cridland-imap-context-03.txt, Isode, June
               2007.

13. Informative References

    [SIEVE]   Guenther, P. and T. Showalter, "Sieve: A Mail Filtering
               Language", RFC 5228, January 2008.

    [QRESYNC]  Melnikov, A., Cridland, D. and C. Wilson, "IMAP4
               Extensions for Quick Mailbox Resynchronization", draft-ietf-lemonade-reconnect-
              client-06.txt (work in progress), September 2007.

Internet-draft                                             February 2008 RFC
               5162, March 2008.

    [EMAIL-ARCH] Crocker, "Internet Mail Architecture", draft-crocker-
               email-arch-10 (work in progress), February 2008.

14. Authors' Addresses

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

    Email: Curtis.King@isode.com

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

    Email: Alexey.Melnikov@isode.com
    Arnt Gulbrandsen
    Oryx Mail Systems GmbH
    Schweppermannstr. 8
    D-81671 Muenchen
    Germany

    Email: arnt@oryx.com

Internet-draft                                             February 2008

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