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Versions: 00 01 02 03 04 05 06 07 RFC 4550

Internet Draft: Lemonade Profile                             S. H. Maes
Document: draft-ietf-lemonade-profile-02.txt                A. Melnikov
Expires: October 2005                                        April 2005

                             Lemonade Profile

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 10 of RFC2026. By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

   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-

   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

   The list of Internet-Draft Shadow Directories can be accessed at


   This document describes a profile (a set of required extensions,
   restrictions and usage modes) of mail protocols such as IMAP and
   Submission. This profile allows clients (especially those that are
   constrained in memory, bandwidth, processing power, or other areas)
   to efficiently use IMAP and Submission to access and submit mail.
   This includes the ability to forward received mail without needing to
   download and upload the mail, to schedule future delivery of a
   message, to optimize submission and to efficiently reconnect in case
   of loss of connectivity with the server.

   The Lemonade profile relies upon extensions to various protocols;
   specifically URLAUTH, CATENATE, Lemonade Command Extensions in the
   IMAP protocol [RFC3501] and BURL in the SUBMIT protocol [RFC2476].

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   In addition, the Lemonade profile contains Lemonade Command
   extensions for quick reconnect and media conversion.

Conventions used in this document

   In examples, "M:", "I:" and "S:" indicate lines sent by the client
   messaging user agent, IMAP e-mail server and SMTP submit server

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

Table of Contents

   Status of this Memo ........................................ 1
   Abstract.................................................... 1
   Conventions used in this document........................... 2
   Table of Contents........................................... 2
   1. Introduction............................................. 3
   2. Forward without download ................................ 3
      2.1. Motivations ........................................ 3
      2.2. Message Sending Overview............................ 3
      2.3. Traditional Strategy................................ 4
      2.4. Step by step description............................ 5
      2.5. Normative statements related to forward without
           download ........................................... 8
      2.6. Additional Considerations........................... 8
      2.7. The fcc problem..................................... 9
   3. Message Submission....................................... 9
      3.1. Future Delivery..................................... 9
      3.2. Pipelining..........................................10
      3.3. TLS.................................................10
      3.4. DSN Support ........................................11
      3.5. Message size declaration............................11
   4. Quick Reconnect scheme...................................11
      4.1. Normative statements related to quick reconnect
           schemes ........................................... 12
   5. Future work............................................. 12
   Security Considerations.................................... 13
   IANA Considerations ....................................... 13
   References................................................. 13
   Version History............................................ 14
   Acknowledgments............................................ 15
   Authors Addresses.......................................... 15
   Intellectual Property Statement............................ 15
   Full Copyright Statement................................... 16

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1.    Introduction

   Lemonade provides enhancements to Internet email to support diverse
   service environments.

   This document describes the lemonade profile that includes:
      - The Lemonade Pull Model that describes exchanges between
        Lemonade Agents to allow clients to submit new email messages
        incorporating content which resides on locations external to
        the client and allow forward without download.
      - Media conversion
      - Quick reconnect

   The organization of this document is as follows.  Section 2 describes
   the Lemonade Pull Model. Section 3 Section 3 describes the Media
   Conversion. Section 4 describes quick reconnect

2.   Forward without download

2.1.     Motivations

   The advent of client/server email using the [RFC3501] and [RFC2821]
   protocols has changed what formerly were local disk operations to
   become excessive and repetitive network data transmissions.

   The Lemonade Pull Model makes use of the [BURL] SUBMIT extension to
   enable access to external sources during the submission of a message.
   In combination with the IMAP [URLAUTH] extension, inclusion of
   message parts or even entire messages from the IMAP mail store is
   possible with a minimal trust relationship between the IMAP and SMTP
   SUBMIT servers.

   Pull has the advantage of maintaining one submission protocol, and
   thus avoids the risk of having multiple parallel and possible
   divergent mechanisms for submission.  Furthermore, by keeping the
   details of message submission in the SMTP SUBMIT server, the Lemonade
   Pull Model can work with other message retrieval protocols such as
   POP, NNTP, or whatever else may be designed in the future.

2.2.     Message Sending Overview

   The act of sending an email message is best thought of as involving
   multiple steps: initiation of a new draft, draft editing, message
   assembly, and message submission.

   Initiation of a new draft and draft editing takes place on the MUA.
   Frequently, users choose to save more complex messages on an
   [RFC3501] server (via the APPEND command with the \Draft flag) for
   later recall by the MUA and resumption of the editing process.

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   Message assembly is the process of producing a complete message from
   the final revision of the draft and external sources.  At assembly
   time, external data is retrieved and inserted in the message.

   Message submission is the process of inserting the assembled message
   into the [RFC2821] infrastructure, typically using the [RFC2476]

2.3.     Traditional Strategy

   Traditionally, messages are initiated, edited, and assembled entirely
   within an MUA, although drafts may be saved to an [RFC3501] server
   and later retrieved from the server.  The completed text is then
   transmitted to an MSA for delivery.

   There is often no clear boundary between the editing and assembly
   process.  If a message is forwarded, its content is often retrieved
   immediately and inserted into the message text.  Similarly, once
   external content is inserted or attached, the content is usually
   retrieved immediately and made part of the draft.

   As a consequence, each save of a draft and subsequent retrieve of the
   draft transmits that entire (possibly large) content, as does message

   In the past, this was not much of a problem, because drafts, external
   data, and the message submission mechanism were typically located on
   the same system as the MUA.  The most common problem was running out
   of disk quota.

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2.4.     Step by step description

   The model distinguishes between a Messaging User Agent (MUA), an
   IMAPv4Rev1 Server ([RFC3501]) and a SMTP submit server ([RFC2476]),
   as illustrated in Figure 1.

        +--------------------+               +--------------+
        |                    | <------------ |              |
        |     MUA (M)        |               | IMAPv4 Rev1  |
        |                    |               |  Server      |
        |                    | ------------> | (Server I)   |
        +--------------------+               +--------------+
               ^  |                             ^     |
               |  |                             |     |
               |  |                             |     |
               |  |                             |     |
               |  |                             |     |
               |  |                             |     |
               |  |                             |     v
               |  |                          +--------------+
               |  |------------------------->|   SMTP       |
               |                             |   Submit     |
               |-----------------------------|   Server     |
                                             |  (Server S)  |
                     Figure 1: Lemonade Pull Model

   The Lemonade Pull Model allows a Messaging User Agent to compose and
   forward an e-mail combining fragments that are located in an IMAP
   server, without having to download these fragments to the server.

   In the [BURL]/[CATENATE] variant of the pull strategy, messages are
   initially composed and edited within an MUA.  The [CATENATE]
   extension to [RFC3501] is then used to upload the message to the IMAP
   server and assemble it, and finally a [URLAUTH] format URL is given
   to a [RFC2476] server with the [BURL] extension for submission.

   The flow involved to support such a use case consists of:
      M: {to I -- Optional} The client connectects to the IMAP server
     and IMAP Fetch of body structures and UIDs (See [RFC3501])

           M: A0051 FETCH 161 (UID BODYSTRUCTURE)

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           I: * 161 FETCH (UID 25627 BODYSTRUCTURE (("TEXT" "PLAIN"
              NIL "7BIT" 1152 23)("TEXT" "PLAIN" ("CHARSET" "US-ASCII"
              "<960723163407.20117h@washington.example.net>" "Compiler
              "BASE64" 4554 73) "MIXED"))
           I: A0051 OK completed

      M: {to I} The client invokes CATENATE (See [CATENATE] for details
     of the semantics and steps û this allows the MUA to create messages
     on the IMAP using new data combined with body structure already
     present on the IMAP server.

     <<EditorÆs note: Draft editing/catenation is omitted for now>>

        M: A0052 CATENATE Sent FLAGS (\Seen $MDNSent) TEXT {738}
        I: + Ready for literal data
        M: Return-Path: <bar@example.org>
        M: Received: from []
        M:           by rufus.example.org via TCP (internal) with
        M:           Thu, 11 Nov 2004 16:57:07 +0000
        M: Message-ID: <419399E1.6000505@example.org>
        M: Date: Thu, 12 Nov 2004 16:57:05 +0000
        M: From: Bob Ar <bar@example.org>
        M: X-Accept-Language: en-us, en
        M: MIME-Version: 1.0
        M: To: foo@example.net
        M: Subject: About our holiday trip
        M: Content-Type: multipart/mixed;
        M:               boundary="------------030308070208000400050907"
        M: --------------030308070208000400050907
        M: Content-Type: text/plain; charset=us-ascii; format=flowed
        M: Content-Transfer-Encoding: 7bit
        M: Our travel agent has sent the updated schedule.
        M: Cheers,
        M: Bob
        M: --------------030308070208000400050907
        M:  URL "imap://imap.example.org/INBOX;UIDVALIDITY=385759045/;
           UID=25627;Section=1.2" TEXT {44}
        I: + Ready for literal data
        M: --------------030308070208000400050907--
        I: A0052 OK [APPENDUID 387899045 45] CATENATE Completed

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        M: A0053 UID STORE XXX +FLAGS.SILENT ($Forwarded)
        I: A0053 OK STORE completed

     << EditorÆs note: Recommend UIDPLUS extension û especially useful
     when appending messages to a non-selected mailbox>>

      M: {to I} The client uses GENURLAUTH command to request and
      I: {to M} The IMAP server returns URLAUTH URL suitable for later
     retrieval with URLFETCH (See [URLAUTH] for details of the semantics
     and steps).

     M: A0054 GENURLAUTH
     uth=submit+bar" INTERNAL
            I: * GENURLAUTH
            I: A0054 OK GENURLAUTH completed

      M: {to S} The client connects to the SMTP submission server and
     starts a new mail transaction. It uses BURL to let the SMTP submit
     server fetch the content of the message from the IMAP server (See
     [BURL] for details of the semantics and steps û this allows the MUA
     to authorize the SMTP submit server to access the message composed
     as a result of the CATENATE step).

     M: EHLO potter.example.org
        S: 250-owlry.example.com
        S: 250-8BITMIME
        S: 250-BURL imap
        S: 250-AUTH PLAIN
        S: 250-DSN
        M: AUTH PLAIN aGFycnkAaGFycnkAYWNjaW8=
        S: 235 2.7.0 PLAIN authentication successful.
        M: MAIL FROM:<bob.ar@example.org>
        S: 250 2.5.0 Address Ok.
        M: RCPT TO:<ron@gryffindor.example.com>
        S: 250 2.1.5 ron@gryffindor.example.com OK.
        M: BURL
     th=submit+bar:internal:91354a473744909de610943775f92038 LAST

      S: {to I} The SMTP submission server uses URLFETCH to fetch the
     message to be sent (See [URLAUTH] for details of the semantics and
     steps. The so-called "pawn-ticket" authorization mechanism uses a
     URI which contains its own authorization credentials.).

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      I: {to S} Provides the message composed as a result of the
     CATENATE step).

     SMTP submission server opens IMAP connection to the IMAP server:

            I: * OK [CAPABILITY IMAP4REV1 URLAUTH] example.com IMAP
     server ready
            S: a001 LOGIN submitserver secret
            I: a001 OK submitserver logged in
            S: a002 URLFETCH "
            I: * URLFETCH "
     th=submit+bar:internal:91354a473744909de610943775f92038" {15065}
            ...message body follows...
            S: a002 OK URLFETCH completed

     << EditorÆs note: The SMTP submission server may LOGOUT>>

      S2: {to M} OK (2XX)

     Submission server returns OK to the MUA:
        S: 250 2.5.0 Ok.

2.5.     Normative statements related to forward without download

   Lemonade compliant mail server MUST therefore respectively support
   support MUST be declared via CAPABILITY [RFC3501].

   Lemonade compliant SMTP submit servers MUST support BURL extensions
   [BURL]. Its support MUST be declared via EHLO [RFC2821].

   A Lemonade client SHOULD support IMAPv4 Rev1 [RFC3501], CATENATE
   [CATENATE], BURL extensions [BURL] and URLAUTH [URLAUTH].

   Additional normative statements are provided in other sections.

2.6.     Additional Considerations

   The so-called "pawn-ticket" authorization mechanism uses a URI which
   contains its own authorization credentials using [URLAUTH].  The
   advantage of this mechanism is that the SMTP submit [RFC2476] server
   can not access any data on the [RFC3501] server without a "pawn-
   ticket" created by the client.  The "pawn-ticket" grants acces only
   to the specific data that the SMTP submit [RFC2476] server is
   authorized to access, can be revoked by the client, and can have a
   time-limited validity.

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2.7.     The fcc problem

   The "fcc problem" refers to a frequent need to deliver a copy of the
   message to a "file carbon copy" recipient.  By far, the most common
   case of fcc is a client leaving a copy of outgoing mail in a "sent
   messages" or "outbox" mailbox.

   In the traditional strategy, the MUA duplicates the effort spent in
   transmitting to the MSA by writing the message to the fcc destination
   in a separate step.  This may be a write to a local disk file or an
   APPEND to a mailbox on an IMAP server.  The latter is one of the
   "excessive and repetitive network data transmissions" which
   represents the "problem" aspect of the "fcc problem".

   The [CATENATE] extension to [RFC3501] addresses the fcc problem.  It
   requires making several simplifying assumptions:
       (1a) there is one, and only one, fcc destination on a single
       (2a) the server which holds the fcc is the same as the server
   which stages the outgoing message for submission
       (3a) it is desired that the fcc be a copy of the complete message
   text with all external data inserted in the message

   << EditorÆs note: [POSTADDRESS] can be used to address issues (1a)
   and (2a). To be done later>>

3.   Message Submission

   LEMONADE compliant SMTP submission server are expected to implement a
   set of SMTP extensions to make message submission efficient.  The
   clients SHOULD take advantage of these features.

3.1.     Future Delivery

   Diverse devices may suffer from intermittent or unpredictable
   connectivity.  Although this does not address the main issues of
   intermittent connectivity, it may be of interest to email users to be
   able to take advantage of future delivery by marking ahead of time a
   message for future submission into the mail system.

   For well-connected devices, the client can hold a message in the
   conceptual "outbox" until an appointed time, and then release the
   message.  Otherwise, the client may need to rely upon a well-
   connected server for this function.

   LEMONADE compliant SMTP submission servers MUST declare via ELHO
   [RFC2821] the support the SMTP service extension for future delivery.

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   If future delivery is not permitted by policy, the server MAY not
   support (and declare) support for future delivery or the SMTP
   submission server may advertise a future delivery interval of zero

   <<EditorÆs note: The latest version of FUTUREDELIVERY doesn't allow a
   compliant server to advertise the interval of 0. This should be
   addressed or remove here >>

   LEMONADE clients requiring the ability to reliably send future
   delivery messages can discover via EHLO if a lemonade SMTP submission
   server supports the SMTP service extension for future deliver [Future

   When dealing with an device that support future delivery, such
   clients may cache or otherwise remember the advertised future
   delivery interval from a previous submission transaction to guide the
   human user into the selection of a valid future delivery interval.

3.2.     Pipelining

   Mobile clients regularly use networks with a relatively high latency.
   Avoidance of round-trips within a transaction has a great advantage
   for the reduction in both bandwidth and total transaction time.  For
   this reason Lemonade servers and clients should use SMTP command
   pipelining for message submission.

   LEMONADE compliant SMTP submission servers MUST support the SMTP
   Service Extensions for Command Pipelining. [REF2197]

   Clients SHOULD pipeline.

3.3.     TLS

   LEMONADE clients may use the BURL extension to SMTP Submission, a
   protocol that requires sending a URLAUTH token to the SMTP submission
   server.  Such a token should be protected from interception to avoid
   a replay attack that will disclose the contents of the message to an
   attacker.  TLS based encryption of the SMTP submission path will
   provide protection against this attack.

   LEMONADE Compliant SMTP submission servers MUST support SMTP Service
   Extension for Secure SMTP over TLS [RFC2487] supporting at least SASL
   PLAIN [RFC2595] authentication.

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   LEMONADE clients SHOULD use TLS protected SMTP submission channels
   when using BURL-based message submission to protect the URLAUTH token
   from interception.

3.4.     DSN Support

   It is expected that a LEMONADE compliant SMTP submission servers
   supports delivery status notifications.

   LEMONADE compliant SMTP submission servers MUST support SMTP service
   extensions for delivery status notifications [RFC3461] and enhanced
   status codes.

   <<EditorÆs note: Enhanced status code may lead to a separate

3.5.     Message size declaration

   LEMONADE compliant SMTP submission servers MUST support the SMTP
   Service Extension for Message Size Declaration [RFC2927]

4.   Quick Reconnect scheme

   Mobile operators usually charge users for the time their mobile
   client gets connected to the Internet and/or for the amount of
   information sent/received. Thus a mobile client should minimize time
   it stays connected to its mail server, which suggests that it should
   disconnect and reconnect frequently.

   Also, it is possible that the mobile client unexpectedly leaves area
   of connectivity, which will require that the client reconnects when
   connectivity returns.

   << EditorÆs note: Discussion about voluntarily versa non-voluntarily
   disconnects might go here>>

   IMAP can be verbose. Usually, in order to synchronize a client with a
   server after a disconnect, the client needs to issue at least the
   following commands: LOGIN/AUTHENTICATE, SELECT and several FETCH
   commands (see [IMAP-DISC] for more details).

   Thus, there is a desire to have a quick reconnect facility in IMAP,
   which will give a mobile client ability to resume a previously
   abandoned session, without the need to perform the full
   synchronization sequence as described above.

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   << EditorÆs note: Example is as per reconnect-02, syntax is subject
   to change>>

         X-DRAFT-W02-RECONNECT] imap.example.com IMAP4rev1 2001.315rh
         at Thu, 15 Jul 2004 11:47:49 -0400 (EDT)
      C: b0002 authenticate login (SID P1234567890 56789
      S: + VXNlciBOYW1lAA==
      C: dGVzdDg=
      S: + UGFzc3dvcmQA
      C: dGVzdDg=
      S: * 464 EXISTS
      S: * 3 RECENT
      S: * OK [UIDVALIDITY 3857529045] UIDVALIDITY
      S: * OK [UIDNEXT 550] Predicted next UID
      S: * OK [HIGHESTMODSEQ 20010715194045007]
      S: * 1 FETCH (UID 1 FLAGS (\Seen))
      test8 authenticated

4.1.     Normative statements related to quick reconnect schemes

   Lemonade compliant mail server MUST support the quick reconnect
   scheme described above.

   A Lemonade client SHOULD support the quick reconnect scheme described

5.   Future work

   Future versions of the Lemonade profile are expected to address
   issues related to access of email form mobile devices, possibly
      - Address editorÆs notes
      - Recommendations in terms of support of Binary and 8-bit MIME
      - Media conversion (static and streamed)
      - transport optimization for low or costly bandwidth and less
        reliable mobile networks
      - server to client notifications outside of the traditional IMAP
      - dealing with firewall and intermediaries
      - compression

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      - filtering

Security Considerations

   Security considerations on the Lemonade Pull Model are discussed
   throughout section 2.

   << EditorÆs note: TBD (Reconnect, etc.)>>

IANA Considerations

   Lemonade profile extensions should be appropriately related to the
   list of IMAP and SMTP parameters.


   [BURL]    Newman, C. "Message Composition", draft-ietf-lemonade-burl-
      XX.txt (work in progress).

   [CATENATE]Resnick, P. "Internet Message Access Protocol (IMAP)
      CATENATE Extension", draft-ietf-lemonade-catenate-XX, (work in

   [Future delivery] White, G. and Vaudreuil, G. "SMTP Submission
      Service Extension for Future Delivery", work in progress, draft-

   [POSTADDRESS] Melnikov, A. "IMAP4 POSTADDRESS extension", work in
      progress, draft-melnikov-imap-postaddress-XX.txt

   [RECONNECT] Melnikov, A. and C. Wilson " IMAP4 extension for quick
      reconnect ", work in progress, draft-ietf-lemonade-reconnect-

   [IMAP-DISC] Melnikov, A.  "Synchronization Operations For
      Disconnected Imap4 Clients", IMAP-DISC, work in progress,  draft-

   [RFC2119] Brader, S.  "Keywords for use in RFCs to Indicate
      Requirement Levels", RFC 2119, March 1997.

   [RFC2180] Gahrns, M.  "IMAP4 Multi-Accessed Mailbox Practice", RFC
      2180, July 1997. http://www.ietf.org/rfc/rfc2180

   [RFC2197] Freed, N. "SMTP Service Extension for Command Pipelining",
      RFC 2197, September 1997. http://www.ietf.org/rfc/rfc2197

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   [RFC2234] Crocker, D. and Overell, P.  "Augmented BNF for Syntax
      Specifications", RFC 2234, Nov 1997.

   [RFC2476] Gellens, R. and Klensin, J., "Message Submission", RFC
      2476, December 1998. http://www.ietf.org/rfc/rfc2476

   [RFC2487] Hoffman, P. "SMTP Service Extension for Secure SMTP over
      TLS ", RFC 2487, Jan 1999.  http://www.ietf.org/rfc/rfc2487

   [RFC2595] Newman, C. "Using TLS with IMAP, POP3 and ACAP ", RFC
      22595, Jun 1999.  http://www.ietf.org/rfc/rfc2585

   [RFC2683] Leiba, B. "IMAP4 Implementation Recommendations", RFC 2683
      Sep 1999.

   [RFC2821]  Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
      April 2001.

   [RFC2822] Resnick, P. "Internet Message Format", RFC 2822, April
      2001.  http://www.ietf.org/rfc/rfc2822

   [RFC3501] Crispin, M. "IMAP4, Internet Message Access Protocol
      Version 4 rev1", RFC 3501, March 2003.

   [RFC3461] Gellens, R. and Klensin, J., "Simple Mail Transfer Protocol
      (SMTP) Service Extension for Delivery Status Notifications
      (DSNs)", RFC 3461, January 2003. http://www.ietf.org/rfc/rfc3461

   [URLAUTH] Crispin, M. and Newman, C., "Internet Message Access
      Protocol (IMAP) - URLAUTH Extension", draft-ietf-lemonade-urlauth-
      XX.txt, (work in progress).

Version History

   Version 02:
   [1] Improved abstract based on review comments as well as change to
   reflect the re-organized content of the present Lemonade profile.
   [2] Editorial improvement of section 2.1
   [3] Addition of section 2.5 with normative statements for lemonade
   compliant clients and servers regarding forward without download.
   [4] Addition of section 3 on message submission.
   [5] Move of media conversion to future work
   [6] Add section 4.1 on normative statements related to quick
   reconnect scheme.

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   [6] Addition of Binary and 8-bit MIME Transport to future work
   [7] Addition of IANA statement
   [8] Update and fix of the references

   Version 01:
   [1] We removed the sections of the profile related to mobile e-mail
      as well as discussion. This will be part of the next version of
      the Lemonade profile work.
   [2] We added detailed examples for the different steps included in
      section 2.4.
   [3] We added section 3 on media conversion
   [4] We added examples on Quick reconnect schemes in section 4.
   [5] We updated the security considerations
   [6] We fixed references based on updates above
   [7] We added a future work section
   [8] We fixed the boiler plate statements on the ôstatus of this memoö
      and ôCopyrightö.


   This document is based on the work in progress described in draft-

Authors Addresses

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

   Alexey Melnikov
   Isode Limited
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex
   TW12 2BX
   Email: Alexey.melnikov@isode.com

Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in

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   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
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