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Versions: 00 01 02 03 04 05 06 07 08 09 10 rfc5551         Informational
Internet Draft: Lemonade Notifications Architecture  R. Gellens (Editor)
Document: draft-ietf-lemonade-notifications-10.txt              Qualcomm
Expires: January 2009                                      July 8,  2008
Intended Status: Informational

                  Lemonade Notifications Architecture

Status of this Memo

    By submitting this Internet-Draft, each author represents that any
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Copyright Notice

    Copyright (C) The IETF Trust (2008).  All Rights Reserved.


    This document discusses how to provide notification and filtering
    mechanisms to mail stores to meet Lemonade goals.

    This document also discusses the use of server to server
    notifications, and how server to server notifications fit into an
    architecture which provides server to client notifications.

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Table of Contents

     1.  Introduction   . . . . . . . . . . . . . . . . . . . . . . .  2
       1.1.  Conventions Used in this Document . . . . . . . . . . .   2
     2.  Notifications logical architecture and LEMONADE Profile  . .  2
     3.  Event-based synchronization   . . . . . . . . . . . . . . .   4
     4.  Push Email . . . . . . . . . . . . . . . . . . . . . . . . .  5
     5.  Server-to-Server Notifications Rationale  . . . . . . . . .   5
       5.1.  Notifications Discussion . . . . . . . . . . . . . . . .  6
       5.2.  Server to Server Notifications Scope  . . . . . . . . .   7
       5.3.  Basic Operation  . . . . . . . . . . . . . . . . . . . .  8
       5.4.  Event order . . . . . . . . . . . . . . . . . . . . . .  10
       5.5.  Reliability  . . . . . . . . . . . . . . . . . . . . . . 10
     6.  Security Considerations   . . . . . . . . . . . . . . . . .  10
     7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . 11
     8.  Normative References  . . . . . . . . . . . . . . . . . . .  11
     9.  Informative References . . . . . . . . . . . . . . . . . . . 11
    10.  Contributors  . . . . . . . . . . . . . . . . . . . . . . .  12
    11.  Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 12
       Appendix A: Changes from Previous Versions  . . . . . . . . .  13
       Intellectual Property Statement  . . . . . . . . . . . . . . . 16
       Full Copyright Statement  . . . . . . . . . . . . . . . . . .  17
       Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . . 17

1.  Introduction

    The lemonade work [LEMONADE-PROFILE] identified a need to provide
    notification and filtering mechanisms for use with IMAP [IMAP].

    In addition, external groups which make use of IETF work also
    expressed such requirements (see, for example, [OMA-LEMONADE-ARCH];
    OMA requirements for within-IMAP ("inband") and out-of-IMAP
    ("outband") server to client notifications are listed in

1.1.  Conventions Used in this Document

    Within this document, the terms "Lemonade Profile" and "Lemonade"
    generally refer to the revised Lemonade Profile document

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2.  Notifications logical architecture and LEMONADE Profile

    The target logical architecture for the LEMONADE Profile is
    described in the revised Lemonade Profile document

    Figure 1 illustrates how notification and filtering fit in the
    context of Lemonade.

                     |              |....
           +=========| Notification |.NF.
           !         |    Server    |....
           !         |              |^ ^
           !         +--------------+! !
     Notif-!                         ! !
   ications!       Filter Protocol   ! !
   Protocol!  !======================! !
           !  !                        !
           !  !    Filter Protocol     !
           !  !=====================\....            +---------+
           !  !          +-----------.NF.---+        |         |
           V  !          |           ....   |        |   MTA   |
        +-----+   IMAP   |....              |  LMTP/ |....     |<==SMTP
        |     | <======> |.VF.  IMAP    ....|  SMTP  |.AF.     |
        | MUA |\   ME-2a |....  Store   .DF.|<=======|....     |
        |     | \        |              ....|        |         |
        +-----+  \       +------------------+        +---------+
                  \              !
                   \             !URLAUTH
              SUBMIT\            !
                     \      +----v-----+
                      \     |          |                +-----+
                       \    | LEMONADE |       SMTP     |     |==>SMTP
                        ===>| Submit   |===============>| MTA |
                    ME-2b   | Server   |                |     |
                            |          |                +-----+

                Figure 1: Filtering mechanism defined in
                    Lemonade Profile architecture.

    In Figure 1, four categories of filters are defined:

    1.   AF:  Administrative Filters:  Created and maintained by mail
    admin.  AF are typically not configured by the user and are used to
    apply policies, content filtering, virus protection, spam filtering,

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    2.   DF:  Deposit Filters:  Executed on deposit of new mail.  Can be
    defined as SIEVE filters [SIEVE].

    3.   VF:  View Filters:  Define which messages are important to a
    client.  May be implemented as pseudo-virtual mailboxes [CONTEXT].
    Clients may use this to restrict which messages they synchronize.

    4.   NF:  Notification Filters:  Determines when out-of-IMAP
    ("outband") notifications are sent to the client.  These filters can
    be implemented either in the message store, or in a separate
    notifications engine.

    Note that when implementing DF or NF using Sieve, the 'enotify'
    [SIEVE-NOTIFY] and likely the 'variables' [SIEVE-VARIABLES] Sieve
    extensions might be needed.

    The filters are manageable by the client as follows:

    *    NF and DF:  When internal to the mail store, these are
    typically implemented using Sieve and hence a Sieve management
    protocol is used for client modifications.  See [MANAGE-SIEVE] for
    more information.  Per-mailbox notifications might be implemented
    using a combination of a primary Sieve script for notifications on
    delivery into a mailbox (e.g., FILEINTO) and a per-mailbox Sieve
    script such as [IMAP-SIEVE] for transfers into a mailbox.  When the
    NF is within a notification server, it is out of scope of Lemonade.

    *    VF: via pseudo-virtual mailboxes as defined in [CONTEXT].

    In Figure 1, the NF are shown both as part of the mail store (for
    example, using Sieve) and as an external notification server.
    Either approach can be used.

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3.  Event-based synchronization

   +----------------+       +---------------+            +------------+
   |    COMPLETE    | (VF)  |   VIEW        |    (NF)    |   PUSH     |
   |   REPOSITORY   | View  |  REPOSITORY   |Notification| REPOSITORY |
   |                |Filters|               |  Filters   |            |
   |   all email    |       |  email to be  |            | important  |
   | in the account |=======|synched by the |=====<?>====| email /    |
   |                |       | mobile client |      |     | events     |
   |                |       |   (CONTEXT)   |      |     |            |
   +----------------+       +---------------+      |     +------------+
                                                   |            |
                                                 IDLE /         |
                                                 NOTIFY    Out-of-IMAP
                                                   |      Notifications
                                                   |            |
                                                   V            V

                  Figure 2:  Filters and Repositories

    For in-IMAP ("inband") notifications, the MUA (client) issues IDLE
    [IDLE], or the successor extension command NOTIFY [NOTIFY]; the
    LEMONADE IMAP server sends notifications as unsolicited responses to
    the client.

    Out-of-IMAP ("outband") notifications are messages sent to the user
    or client not through IMAP.  When directed at the user, they are
    human-consumable and intended to alert the user.  When directed at
    the client, they are machine-consumable and may be acted upon by the
    receiver in various ways, for example, fetching data from the mail
    store or resynchronizing one or more mailboxes, updating internal
    state information, and alerting the user.

4.  Push Email

    A good user experience of "push email" requires that when
    "interesting" events occur in the mail store, the client is informed
    so that it can connect and resynchronize.  The Lemonade Profile
    [LEMONADE-PROFILE] contains more information, especially in the
    Section titled "External Notifications".

5.  Server-to-Server Notifications Rationale

    With server to server notifications, a mail system generates event
    notifications.  These notifications describe mailbox state change
    events such as arrival of a new message, mailbox full, and so forth.

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    See [MSGEVENT] for a list of such events.

    These state change notifications are sent to a notification system,
    which may generate alerts or notifications for delivery to one or
    more clients or the user.

    Server to server notifications allow the mail system to generate end
    user or client notifications without needing to keep track of
    notification settings for users or clients; the notification system
    maintains notification preferences for clients and users.

    Using server to server notifications, the mail system can provide
    the end user with a unified notification experience (the same look
    and feel for all messaging systems' accounts, such as email and
    voice mail), while allowing smooth integration of additional
    messaging systems.

5.1.  Notifications Discussion

    The POP3 and IMAP4 Internet mail protocols allow mail clients to
    access and manipulate electronic mail messages on mail systems.  By
    definition and scope, these protocols do not provide off-line
    methods to notify an end user when the mailbox state changes.  Nor
    does either protocol define a way to aggregate the status within the
    end user's various mailboxes.

    The desire for this functionality is obvious.  For example, from the
    very early days of electronic mail, various notifications mechanisms
    have been used, including login shell checks, and simple hacks such
    as [BIFF].

    To provide an end user with unified notifications and one
    centralized message-waiting indication (MWI), notification
    mechanisms are needed which aggregate the information of all the
    events occurring on the end user's different messaging systems.

    Server to server notifications allow the messaging system to send
    state change events to the notification system when something
    happens in or to an end user's mailbox.

    Notification systems can be broadly grouped into three general
    architectures: external smart clients, intrinsic notification, and
    separate notification mechanisms.

    External smart clients are agents independent of the mail system
    that periodically check mailbox state (or receive notifications, for
    example via IMAP IDLE) and inform the user or the user's mail
    client.  Many such systems have been used over the years, including

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    login shells that check the user's mail spool, laptop/desktop tiny
    clients that periodically poll the user's mail servers, etc.

    Intrinsic notification is any facility within a mail system that
    generates notifications, for example the server component of [BIFF],
    or, for more modern systems, the recent Sieve extensions for
    notifications [SIEVE-NOTIFY].

    Separate notification systems decouple the state change event
    notification from the end-user or client notification, allowing a
    mail system to do the former, and specialized systems (such as those
    which handle presence) to be responsible for the latter.  This
    separation is architecturally cleaner, since the mail system only
    needs to support one additional protocol (for communication to the
    notification system) instead of multiple notification delivery
    protocols, and does not need to keep track of which clients and
    which users are interested in which events.  It also allows
    notifications to be generated for any service, not just electronic
    mail.  However, it requires a new service (the notification system)
    and the mail system needs to support an additional protocol (to
    communicate with the notification system).

    In addition to any external notification mechanisms, Sieve can be
    used for notifications [SIEVE-NOTIFY].  Since many mail systems
    already provide Sieve support, it is often a fairly easy and quick
    deployment option to provide a useful form of notifications.

5.2.  Server to Server Notifications Scope

    For the purposes of the Lemonade work, the scope of server to server
    notifications is limited to communications between the mail system
    and the notification system (the third architectural type described
    in Section 5.1).  Communication between the notification system and
    the end user or devices (which might use SMS, WAP Push, instant
    messaging, etc.) is out of scope.  Likewise, the scope generally
    presumes a security relationship between the mail system and the
    notification system.  Thus the security relationship then becomes
    the responsibility of the notification system.  However, the
    specifics of security, trust relationships, and related issues
    depend on the specifics of both server to server notifications and
    notification systems.

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    Figure 3 shows the context of server to server notifications; only
    the left side is in scope for Lemonade:

              +--------+                                 +--------+
       New    |        |_                                |  SMS   |
      Message |  Mail  | \                               |Gateway |
     -------> |Server 1|  \                            __|        |
              +--------+   \                          /  +--------+
                          ^ \                        /
                          |  \                      / ^
                          |   \  +--------------+  /  |  +--------+
              +--------+  |    \ |              | /   |  |  MWI   |
      Read    | Voice  |  |     -| Notification |/    |  |Gateway |
     Message  |  Mail  |-------->|    Server    |------->|        |
     -------> | Server |  | ^  __|              |\  ^ |  +--------+
              +--------+  | | /  |(out of scope)| \ | |
                          | |/   |              |  \| |
                          | / ^  +--------------+ ^ \ |
                          |/| |                \  | |\|
              +--------+  / | |                 \ | | \  +--------+
      Mailbox |        | /| | |                  \| | |\ |  Wap   |
      Full    |  Mail  |/ | | |                 ^ \ | | \|  Push  |
     -------> |Server 2|  | | |                 | |\| |  |Gateway |
              +--------+  | | |                 | | \ |  +--------+
                          | | |                 | | |\|
                          | | |                 | | | \
                          | | |                 | | | |\ +--------+
                          | | |                 | | | | \| IM     |
                          | | |                 | | | |  |Gateway |
                          | | |                 | | | |  |        |
                          | | |                 | | | |  +--------+
                          | | |                 | | | |
                          | | |                 | | | |
                        Server to                OTHER
                          Server               PROTOCOLS
                      Notifications          (out of scope)
                      (in scope)

           Figure 3: Scope of server to server notifications

5.3.  Basic Operation

    The mail system sends state change event notifications to the
    notification system (which in turn might notify a client or end
    user) for events that occur in the end user's mailboxes.  Each such
    notification, referring to a single mailbox event, is called a state
    change event.

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    The state change event contains data regarding the mailbox event
    which has occurred.  The state change event describes the change,
    but normally does not specify how or if the end user or client is
    notified; this allows the end user and client notification
    preferences to be maintained only within the notification server.

    From the Lemonade viewpoint, out-of-IMAP (outband) notifications are
    usually desired only when the client is not connected to the IMAP
    server (since inband notifications are used when there is an IMAP
    connection).  Thus, it is helpful for the mail system to be able to
    inform the notification system when the user logs in or out, and
    which client is used (when this information is available).

    When Sieve is used, the Sieve engine might have access to this

    A message is generated by the message store as a result of a state
    change event.  This message may be delivered to the end user, a
    client, or to an external notification server which might deliver an
    equivalent message to the user or to a client.

    Within the context of Lemonade profile (Figure 1), the event is
    filtered by NF.  That is, the Notification Filters logically
    determine which state change events cause notification to the user
    or client.

    Notifications allow for a rich end user experience.  This might
    include conveying mailbox status, new message attributes, etc., to
    the user or client independent of the client's connection to the
    mail store.

    Notifications also allow for different Message Waiting Indicator
    (MWI) behaviors (e.g., turn MWI indication off after all the
    messages in all the end user's mailboxes have been read, should such
    an unlikely thing occur in the real world).

    The payload of a notification might include a URL referring to the
    message which caused the event, possibly using URLAUTH [URLAUTH].

    As state change events occur in the mail store, they are filtered,
    which is to say matched against client or user preferences.  As a
    result, a notification may or may not be generated for delivery to
    the user or client.

    In the most general case, the mail system sends bulk state change
    events to an external notification server, and it is the
    notification server that filters the events by matching against the
    user's or client's preferences.

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    In the most mail-specific case, the mail system performs the
    filtering itself, for example using Sieve.

5.4.  Event order

    For Lemonade profile, the event order is generally not important.
    By including information such as the modification sequence
    identifier (called a modseq or mod-sequence) [CONDSTORE] in
    notifications, the receiving client can quickly and easily determine
    if it has already processed the triggering event (for example, if a
    notification arrives out of order, or if the client has

    For generic server to server notifications, the order is likely to
    matter and the mail system needs to provide notifications to the
    notification system in the order that they occur.

5.5.  Reliability

    For the Lemonade profile, lost or delayed notifications to the
    client are tolerated.  A client can resynchronize its state
    (including that reported by any missing events) when it next
    connects to the server.

    For generic server to server notifications, it is assumed that the
    data in a state change event is important, and therefore a high
    level of reliability is needed between the mail system and any
    external notification systems.

6.  Security Considerations

    Notification content (payload) needs to be protected against
    eavesdropping and alteration when it contains specific information
    from messages, such as the sender.

    Even when the content is trivial and does not contain
    privacy-sensitive information, guarding against denial of service
    attacks may require authentication or verification of the
    notification sender.

    Protocols which manipulate filters need mechanisms to protect
    against modification by as well as disclosure to unauthorized
    entities.  For example, a malicious entity might try to delete
    notifications the user wants, or try to flood the target device with
    notifications to incur usage charges, or prevent normal use.  In
    addition, the filters themselves might contain sensitive information

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    or reveal interpersonal or inter-organizational relationships, as
    well as e-mail addresses.

7.  IANA Considerations


8.  Normative References

    [IMAP] Crispin, M. "IMAP4, Internet Message Access Protocol Version
    4 rev1", RFC 3501, March 2003. http://www.ietf.org/rfc/rfc3501

    [LEMONADE-PROFILE] D. Cridland, A. Melnikov, S. Maes, "LEMONADE
    profile bis", draft-ietf-lemonade-profile-bis-08.txt, (work in

9.  Informative References

    [BIFF] Gellens, R., "Simple New Mail Notification", RFC 4146, August

    [CONTEXT] D. Cridland, C. King, "Contexts for IMAP4",
    draft-cridland-imap-context-05.txt (work in progress).

    [CONDSTORE] Melnikov, A., Hole, S., RFC 4551, June 2006.

    [IMAP-SIEVE] Leiba, B., "Support for Sieve in Internet Message
    Access Protocol (IMAP4)", draft-ietf-lemonade-imap-sieve-05.txt
    (work in progress).

    [MANAGE-SIEVE] Martin, T. and A. Melnikov, "A Protocol for Remotely
    Managing Sieve Scripts", draft-martin-managesieve-08.txt, (work in

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

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

    [NOTIFY] C. King, A. Melnikov, A. Gulbrandsen, "The IMAP NOTIFY
    Extension", draft-ietf-lemonade-imap-notify-05.txt, (work in

    [OMA-LEMONADE-ARCH], E. Burger, G. Parsons, "LEMONADE Architecture
    -- Supporting OMA Mobile Email (MEM) using Internet Mail",
    draft-ietf-lemonade-architecture-01.txt, (work in progress).

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    [OMA-ME-RD] Open Mobile Alliance Mobile Email Requirement Document,
    (Work in progress). http://www.openmobilealliance.org/

    [SIEVE] P. Guenther, T. Showalter, "Sieve:  Sieve:  An Email
    Filtering Language", RFC 5228, January 2008.

    [SIEVE-NOTIFY] A. Melnikov, B. Leiba, W. Segmuller, T. Martin,
    "SIEVE Email Filtering:  Extension for Notifications",
    draft-ietf-sieve-notify-12.txt, (work in progress).

    [SIEVE-VARIABLES] Homme, K., "Sieve Email Filtering:  Variables
    Extension", RFC 5229, January 2008.

    [URLAUTH] Crispin, M. and Newman, C., "Internet Message Access
    Protocol (IMAP) - URLAUTH Extension", RFC 4467, May 2006.

10.  Contributors

    The original (and longer and more detailed) version of this document
    was authored by Stephane H. Maes and Ray Cromwell of Oracle

    The current and original authors want to thank all who have
    contributed key insight in notifications and filtering and have
    authored specifications or drafts used in this document.

    The current and original authors want to thank the authors of the
    original work on Server To Server Notification Protocol Requirements
    (draft-ietf-lemonade- notify-s2s-00) some of whose material has been
    incorporated in the present document, and in particular, Gev

11.  Authors' Addresses

    Randall Gellens
    QUALCOMM Incorporated
    5775 Morehouse Drive
    San Diego, CA  92121

    Stephane H. Maes
    Oracle Corporation
    500 Oracle Parkway
    M/S 4op634
    Redwood Shores, CA 94065
    Phone: +1-650-607-6296

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    Email: stephane.maes@oracle.com

    Ray Cromwell
    Oracle Corporation
    500 Oracle Parkway
    Redwood Shores, CA 94065

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Appendix A:  Changes from Previous Versions


    version -10:
    o   Rewording of IMAP-SIEVE reference in Section 2.

    version -09:
    o   Reworded and moved sieve-variables reference in Section 2.
    o   Reworded imap-sieve reference in Section 2.
    o   Changed reference to Profile-Bis from Section 4.1.2 to "External
    o   Reworded mention of security relationship responsibility in
        Section 5.2.

    version -08:
    o   Removed mention of vacation notices in Section 2, Figure 1
        (description of DF category of filters) since vacation notices,
        while often a function of delivery filters, are out of scope of
    o   Improved text in Section 5 and 5.1.
    o   Renamed Sections 5 and 5.1.
    o   Deleted old section 5.4.1 (Generic Case).
    o   Reworded Section 1 (Introduction).
    o   Added Section 1.1 to explain that "Lemonade Profile" here refers
        to profile-bis.
    o   Deleted reference to original (non-bis) Profile.
    o   Improved wording in Section 3.
    o   Split latter part of Section 5.1 into new Section 5.2 (Scope).
    o   Combined Sections 5.3 (Notification payloads) and 5.4 (Server to
        server notification protocol details), as the sections no longer
        discuss separate topics, nor were they any longer related to
        their titles.
    o   Updated references to current versions.

    version -07:
    o   Fixed bugs in NF arrows in Figure 1.
    o   Edited text following Figure 1 to try and make it more clear
        that NF can be either in the mail store (using Sieve) or in the
        notifications engine (using mechanisms out of scope to
    o   Changed Acknowledgments section to Contributors to better
        reflect Stephan's and Ray's text.
    o   Tweaked text in Section 5.
    o   Added mention of filter protection to Security Considerations.

    version -06:
    o   Added pointer to profile-bis 5.4.2 ("External Notifications")
    o   Cleaned up references, split into Normative/Informative

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    o   Reworded old Section 4 ("Event-based synchronization"), added
        NOTIFY and IDLE references
    o   Deleted Section 1 ("Conventions Used in this Document") as none
        of it applied any longer.
    o   Reworded and reworked old Section 5 ("Server to server
        notifications considerations") and its subsections and added
        reference to msgevents draft and RFC 4146.
    o   Changed "notification request" to "state change event".
    o   Added "within-IMAP" and "out-of-IMAP" to most occurrences of
        "inband" and "outband".
    o   Added mention of user login/logout as a state change that can be
        used to trigger outband notifications.
    o   Redid Figure 1 to make it easier to understand, and also to show
        that NF might be within the mail store (Sieve) or in an external
        notification mechanism.
    o   Deleted section 5.3 ("Server to server terminology").
    o   Deleted reference to
    o   Major changes to section 5.4 ("Notification payloads") and
        section 5.5 ("Server to server notification protocol details").
    o   Deleted section 5.5.2 ("Abstracted notification protocol"),
        section 5.5.3 ("Exception Handling"), and section 5.6 ("Server
        to server complementary information").
    o   Rewrote section 5.7 ("Event orders") and added reference to RFC
    o   Rewrote section 5.8 ("Reliability").
    o   Added references to sieve-notify, IMAP NOTIFY, IMAP, and others.
    o   Deleted many, many references.
    o   Updated references.
    o   Corrected references.
    o   Split references into normative and informative.
    o   Added reference to draft-ietf-lemonade-architecture-00.txt.
    o   Rewrote Introduction.
    o   Changed draft name from "... and Filters" to "...

    version -05:
    o   Significant deletion of sections, per

    version -04:
    o   Update dates, slight reformatting, add editor's note for

    version -03:
    o   Updated examples to use new METADATA syntax
    o   Drop CLEARIDLE and reference A. Melnikov's IMAP-EVENTS
    o   XEMN notification format extended to with event and view

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    o   View filter is a work in progress.  Several proposals are being
        discussed, so the draft has been revised to try and capture high
        level requirements (e.g. out of band notifications must be able
        to identify which view an event occurred for)
    o   Added notification protocol details and reference

    version -02:
    o   LPROVISION/LGETPREFS/LSETPREFS removed in favor of mailbox
    o   Updated inband notification section to include discussion of
    o   EMN payload clarified for both wakeup and extended formats.
    o   Some reference clean-up
    o   Add server to server notifications based on the expired draft

    version -01:
    o   Move SMS / WAP examples to an informative appendix.
    o   Restrict the exchange of keys via LPROVISION to secure
    o   Differentiate ANNOTATE from LPROVISION on that basis.

    versin -00:
    o   Initial release

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