path: root/doc/rfc/rfc5550.txt

Network Working Group                                   D. Cridland, Ed.
Request for Comments: 5550                              A. Melnikov, Ed.
Obsoletes: 4550                                            Isode Limited
Updates: 4469, 4467                                         S. Maes, Ed.
Category: Standards Track                                         Oracle
                                                             August 2009


                         The Internet Email to
        Support Diverse Service Environments (Lemonade) Profile

Abstract

   This document describes a profile (a set of required extensions,
   restrictions, and usage modes), dubbed Lemonade, of the IMAP, mail
   submission, and Sieve protocols.  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 optimize submission, and to efficiently resynchronize in
   case of loss of connectivity with the server.

   The Lemonade Profile relies upon several extensions to IMAP, Sieve,
   and Mail Submission protocols.  The document also defines a new IMAP
   extension and registers several new IMAP keywords.

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.






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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1. Introduction ....................................................3
   2. Conventions Used in This Document ...............................4
   3. Summary of the Required Support .................................4
      3.1. Lemonade Submission Servers ................................4
      3.2. Lemonade Message Stores ....................................5
      3.3. Lemonade Message Delivery Agents ...........................7
   4. Lemonade Submission Servers .....................................7
      4.1. Forward without Download ...................................7
      4.2. Pipelining .................................................8
      4.3. DSN Support ................................................8
      4.4. Message Size Declaration ...................................8
      4.5. Enhanced Status Code Support ...............................8
      4.6. Encryption and Compression .................................8
   5. Lemonade Message Stores .........................................9
      5.1. Quick Resynchronization ....................................9
      5.2. Message Part Handling ......................................9
      5.3. Compression ...............................................10
      5.4. Notifications .............................................10
      5.5. Searching and View Filters ................................12
      5.6. Mailbox Handling ..........................................12
      5.7. Forward without Download ..................................12
      5.8. Additional IMAP Extensions ................................13
      5.9. Registration of $Forwarded IMAP Keyword ...................13
      5.10. Registration of $SubmitPending and $Submitted
            IMAP Keywords ............................................13
      5.11. Related IMAP Extensions ..................................14
   6. Lemonade Message Delivery Agents ...............................14
   7. Lemonade Message User Agents ...................................15
   8. Forward without Download .......................................16
      8.1. Motivations ...............................................16
      8.2. Message Sending Overview ..................................16
      8.3. Traditional Strategy ......................................17
      8.4. A New Strategy ............................................18
      8.5. Security Considerations for Pawn-Tickets ..................27



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      8.6. Copies of Sent Messages: The fcc Problem ..................27
   9. Deployment Considerations ......................................28
   10. Security Considerations .......................................28
      10.1. Confidentiality Protection of Submitted Messages .........28
      10.2. TLS ......................................................29
      10.3. Additional Extensions and Deployment Models ..............29
   11. IANA Considerations ...........................................30
   12. Changes since RFC 4550 ........................................30
   13. Acknowledgements ..............................................31
   14. References ....................................................31
      14.1. Normative References .....................................31
      14.2. Informative References ...................................35
   Appendix A.  Errata  ..............................................37

1.  Introduction

   The Lemonade Profile, or simply Lemonade, provides enhancements to
   Internet email to support diverse service environments.  Lemonade
   mail servers provide both a Lemonade Submission Server and a Lemonade
   Message Store, which are based on the existing [SUBMIT] and [IMAP]
   protocols, respectively.  They MAY also include a Lemonade Message
   Delivery Agent, which provides delivery-time filtering services based
   on [SIEVE].

   This document describes the Lemonade Profile that includes:

   o  General common enhancements to Internet Mail, described in 5 and
      4.

   o  "Forward without download" that describes exchanges between
      Lemonade clients and servers to allow submitting new email
      messages incorporating content that resides on locations external
      to the client, described in Section 8.

   o  Quick mailbox resynchronization, described in Section 5.1.

   o  Extensions to support more precise, and broader, notifications
      from the store in support of notifications and view filters,
      described in 5.4.1 and 5.5.

   o  Delivery-time filtering in support of typical mail management use
      cases, as described in Section 3.3.

   The LEMONADE WG used the architecture shown in [LEMONADE-ARCH] to
   develop the Lemonade Profile.






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   It is intended that the Lemonade Profile support realizations of the
   OMA's mobile email enabler (MEM) (see [OMA-MEM-REQ] and
   [OMA-MEM-ARCH]) using Internet Mail protocols defined by the IETF.

2.  Conventions Used in This Document

   In examples, "M:", "I:", and "S:" indicate lines sent by the client
   Message User Agent, IMAP email server, and SMTP submit server,
   respectively.

   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 [KEYWORDS].

   Other capitalized words are typically names of extensions or commands
   -- these are uppercased for clarity only, and are case-insensitive.

   This document uses terminology defined in [RFC5598].  See [RFC5598]
   for further details on Email Architecture.

   All examples in this document are optimized for Lemonade use and
   might not represent examples of proper protocol usage for a general
   use Submit/IMAP client.  In particular, examples assume that Submit
   and IMAP servers support all Lemonade extensions described in this
   document, so they do not demonstrate fallbacks in the absence of an
   extension.

3.  Summary of the Required Support

3.1.  Lemonade Submission Servers

   Lemonade Submission Servers MUST provide a service as described in
   [SUBMIT], and MUST support the following.  Note that the Lemonade
   Profile imposes further requirements for some cases, detailed in the
   sections cited.
















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        +---------------------+--------------------+--------------+
        |    SMTP extension   |      Reference     | Requirements |
        +---------------------+--------------------+--------------+
        |       8BITMIME      |   [SMTP-8BITMIME]  |  [SMTP-BURL] |
        |         AUTH        |     [SMTP-AUTH]    |   [SUBMIT]   |
        |      BINARYMIME     |  [SMTP-BINARYMIME] |  Section 4.1 |
        |      BURL imap      |     [SMTP-BURL]    |   Section 8  |
        |       CHUNKING      |  [SMTP-BINARYMIME] |  Section 4.1 |
        |         DSN         |     [SMTP-DSN]     |  Section 4.3 |
        | ENHANCEDSTATUSCODES | [SMTP-STATUSCODES] |  Section 4.5 |
        |      PIPELINING     |  [SMTP-PIPELINING] |  Section 4.2 |
        |         SIZE        |     [SMTP-SIZE]    |  Section 4.4 |
        |       STARTTLS      |     [SMTP-TLS]     |  Section 4.6 |
        +---------------------+--------------------+--------------+

3.2.  Lemonade Message Stores

   Lemonade Message Stores MUST provide a service as described in
   [IMAP], and MUST support the following.  Note that the Lemonade
   Profile imposes further requirements for some cases, detailed in the
   sections cited.






























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       +------------------------+------------------+---------------+
       |     IMAP extension     |     Reference    |  Requirements |
       +------------------------+------------------+---------------+
       |         BINARY         |   [IMAP-BINARY]  |  Section 5.2  |
       |        CATENATE        |  [IMAP-CATENATE] |  Section 5.7  |
       |    COMPRESS=DEFLATE    |  [IMAP-COMPRESS] |  Section 5.3  |
       |        CONDSTORE       | [IMAP-CONDSTORE] |  Section 5.1  |
       |     CONTEXT=SEARCH     |  [IMAP-CONTEXT]  |  Section 5.5  |
       |      CONTEXT=SORT      |  [IMAP-CONTEXT]  |  Section 5.5  |
       |         CONVERT        |  [IMAP-CONVERT]  |  Section 5.2  |
       |         ENABLE         |   [IMAP-ENABLE]  |  Section 5.1  |
       |         ESEARCH        |  [IMAP-ESEARCH]  |  Section 5.5  |
       |          ESORT         |  [IMAP-CONTEXT]  |  Section 5.5  |
       |       I18NLEVEL=1      |    [IMAP-I18N]   |  Section 5.8  |
       |          IDLE          |    [IMAP-IDLE]   | Section 5.4.1 |
       |        LITERAL+        |  [IMAP-LITERAL+] |  Section 5.8  |
       |        NAMESPACE       | [IMAP-NAMESPACE] |  Section 5.6  |
       |         NOTIFY         |   [IMAP-NOTIFY]  | Section 5.4.1 |
       |         QRESYNC        |  [IMAP-QRESYNC]  |  Section 5.1  |
       |         SASL-IR        |  [IMAP-SASL-IR]  |  Section 5.8  |
       |          SORT          |    [IMAP-SORT]   |  Section 5.5  |
       |        STARTTLS        |      [IMAP]      |       -       |
       |         UIDPLUS        |  [IMAP-UIDPLUS]  |  Section 5.7  |
       |         URLAUTH        |  [IMAP-URLAUTH]  |  Section 5.7  |
       |       URL-PARTIAL      |   Section 5.7.1  |  Section 5.7  |
       |   $Forwarded keyword   |         -        |  Section 5.9  |
       | $SubmitPending keyword |         -        |  Section 5.10 |
       |   $Submitted keyword   |         -        |  Section 5.10 |
       +------------------------+------------------+---------------+

   In addition to this list, any Lemonade Message Stores MUST send the
   CAPABILITY response code (see Section 7.1 of [IMAP]) in the initial
   server greeting and after the LOGIN/AUTHENTICATE commands.


















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3.3.  Lemonade Message Delivery Agents

   Lemonade Message Delivery Agents MUST support Sieve mail filtering
   language as described in [SIEVE], and MUST support the following
   Sieve extensions.  Note that the Lemonade Profile imposes further
   requirements for some cases, detailed in the sections cited.

   +------------------------------+--------------------+--------------+
   |        Sieve extension       |      Reference     | Requirements |
   +------------------------------+--------------------+--------------+
   |            ENOTIFY           |   [SIEVE-NOTIFY]   |   Section 6  |
   |          IMAP4FLAGS          | [SIEVE-IMAP4FLAGS] |   Section 6  |
   |          RELATIONAL          | [SIEVE-RELATIONAL] |   Section 6  |
   |           VACATION           |  [SIEVE-VACATION]  |   Section 6  |
   |           VARIABLES          |  [SIEVE-VARIABLES] |   Section 6  |
   | comparator-i;unicode-casemap |  [UNICODE-CASEMAP] |   Section 6  |
   +------------------------------+--------------------+--------------+

   Lemonade Message Delivery Agents should also consider supporting a
   Sieve script management protocol, such as [MANAGESIEVE].

4.  Lemonade Submission Servers

   All Lemonade Submission Servers implement the Mail Submission
   protocol described in [SUBMIT], which is in turn a specific profile
   of [ESMTP].  Therefore, any MUA designed to submit email via [SUBMIT]
   or [ESMTP] will interoperate with Lemonade Submission Servers.

   In addition, Lemonade Submission Servers implement the following set
   of SMTP and Submission extensions to increase message submission
   efficiency.

4.1.  Forward without Download

   In order to optimize network usage for the typical case where message
   content is copied to, or sourced from, the IMAP store, Lemonade
   provides support for a suite of extensions collectively known as
   "forward without download", discussed in detail in Section 8.

   Lemonade Submission Servers MUST support BURL [SMTP-BURL], 8BITMIME
   [SMTP-8BITMIME], BINARYMIME [SMTP-BINARYMIME], and CHUNKING
   [SMTP-BINARYMIME] SMTP extensions.

   BURL MUST support URLAUTH type URLs [IMAP-URLAUTH], and thus MUST
   advertise the "imap" option following the BURL EHLO keyword (see
   [SMTP-BURL] for more details).





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4.2.  Pipelining

   Some clients regularly use networks with a relatively high latency,
   such as mobile or satellite-based networks.  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-
   compliant mail Submission Servers MUST support the SMTP service
   extensions for command pipelining [SMTP-PIPELINING].

4.3.  DSN Support

   Lemonade-compliant mail Submission Servers MUST support SMTP service
   extensions for delivery status notifications [SMTP-DSN].

4.4.  Message Size Declaration

   There is a distinct advantage in detecting failure cases as early as
   possible in many cases, such as where the user is charged per octet,
   or where bandwidth is low.  This is especially true of large message
   sizes.

   Lemonade Submission Servers MUST support the SMTP service extension
   for message size declaration [SMTP-SIZE].

   Lemonade Submission Servers MUST expand all BURL parts before
   evaluating if the supplied message size is acceptable.

   A Lemonade-capable client SHOULD use message size declaration.  In
   particular, the client MUST NOT send a message to a mail Submission
   Server if it knows that the message exceeds the maximal message size
   advertised by the Submission Server.  When including a message size
   in the MAIL FROM command, the client MUST use a value that is at
   least as large as the size of the assembled message data after
   resolution of all BURL parts.

4.5.  Enhanced Status Code Support

   Lemonade-compliant mail Submission Servers MUST support the SMTP
   service extension for returning enhanced error codes
   [SMTP-STATUSCODES].  These allow a client to determine the precise
   cause of failure.

4.6.  Encryption and Compression

   Lemonade-compliant mail Submission Servers MUST support the SMTP
   service extension for secure SMTP over Transport Layer Security (TLS)
   [SMTP-TLS].




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   Support for the DEFLATE compression method, as described in
   [TLS-COMP], is RECOMMENDED.

5.  Lemonade Message Stores

   All Lemonade Message Stores implement the Internet Message Access
   Protocol, as defined in [IMAP].  Therefore, any MUA written to access
   messages using the facilities described in [IMAP] will interoperate
   with a Lemonade Message Store.

   In addition, Lemonade Message Stores provide a set of extensions to
   address the limitations of some clients and networks.

5.1.  Quick Resynchronization

   Resynchronization is a costly part of an IMAP session, and mobile
   networks are generally more prone to unintended disconnection, which
   in turn makes this problem more acute.  Therefore, Lemonade Message
   Stores provide a suite of extensions to reduce the synchronization
   cost.

   Lemonade-compliant IMAP servers MUST support the CONDSTORE
   [IMAP-CONDSTORE], the QRESYNC [IMAP-QRESYNC], and the ENABLE
   [IMAP-ENABLE] extensions.  These allow a client to quickly
   resynchronize any mailbox by asking the server to return all flag
   changes and expunges that have occurred since a previously recorded
   state.  This can also speed up client reconnect in case the transport
   layer is cut, whether accidentally or as part of a change in network.

   When implementing QRESYNC [IMAP-QRESYNC], client and servers need to
   also comply with errata submitted for this document (see Appendix A).

   [IMAP-SYNC-HOWTO] details how clients perform efficient mailbox
   resynchronization.

5.2.  Message Part Handling

   The handling of message parts, especially attachments, represents a
   set of challenges to limited devices, both in terms of the bandwidth
   used and the capability of the device.

   Lemonade-compliant IMAP servers MUST support the BINARY [IMAP-BINARY]
   extension.  This moves MIME body part decoding operations from the
   client to the server.  The decoded data is equal to or less in size
   than the encoded representation, so this reduces bandwidth
   effectively.





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   [IMAP-BINARY] allows for servers to refuse to accept uploaded
   messages containing binary data, by not accepting the Binary content-
   transfer-encoding; however, Lemonade-compliant IMAP servers SHALL
   always accept binary encoded MIME messages in APPEND commands for any
   folder.

   [IMAP-CONVERT] MUST also be supported by servers, which allows
   clients to request conversions between media types, and allows for
   scaling images, etc.  This provides the ability to view attachments
   (and sometimes body parts) without the facility to cope with a wide
   range of media types, or to efficiently view attachments.

5.3.  Compression

   Lemonade Message Stores SHOULD support the Deflate compression
   algorithm for TLS, as defined in [TLS-COMP], in order to facilitate
   compression at as low a level as possible.

   However, the working group acknowledges that for many endpoints, this
   is a rarely deployed technology, and as such, Lemonade Message Stores
   MUST provide [IMAP-COMPRESS] support for fallback application-level
   stream compression, where TLS is not actively providing compression.

5.4.  Notifications

   The addition of server-to-client notifications transforms the
   Lemonade Profile into an event-based synchronization protocol.
   Whenever an event occurs that interests the MUA, a notification can
   be generated.  The Lemonade WG used the notifications architecture
   shown in [LEMONADE-NOTIFICATIONS] to develop the Lemonade Profile.

   If the MUA is connected to the IMAP server, inband notifications are
   generated using the facilities outlined in Section 5.4.1.

   When the MUA is not connected, the notification filter generates an
   outband notification.  The notification filter may be considered as
   acting on a push email repository.

   If the MUA is not connected, and outband notification is disabled,
   the client must perform a quick-sync on reconnect to determine
   mailbox changes, using the mechanisms outlined in Section 5.1.










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5.4.1.  IMAP Notifications

   Lemonade Message Stores MUST support the IDLE [IMAP-IDLE] extension.
   The extension allows clients to receive unsolicited notifications
   about changes in the selected mailbox, without needing to poll for
   changes.  The responses forming these notifications MUST be sent in a
   timely manner when such changes happen.

   Lemonade Message Stores also provide the NOTIFY extension described
   in [IMAP-NOTIFY], which allows clients to request specific event
   types to be sent immediately to the client, both for the currently
   selected folder and others.  Such event types include message
   delivery and mailbox renames.

5.4.2.  External Notifications

   Lemonade and TCP provide for long-lived idle connections between the
   client and mail store, allowing the server to push notifications
   within IMAP.  Some mobile networks support dormancy, which shuts down
   the radio traffic channel during idle periods to conserve handset and
   network resources, while maintaining IP and TCP state.  (See the
   [LEMONADE-DEPLOYMENTS] document for more information.)

   However, there are environments where the email client cannot remain
   active indefinitely, or where it is not advisable (or even always
   possible) for TCP connections to the server to remain up while idle
   for extended periods.  In these situations, a good user experience
   requires that when "interesting" events occur in the mail store, the
   client be informed so that it can connect and resynchronize.  At an
   absolute minimum, this requires that at least the arrival of new mail
   generate some sort of wake-up to the email client.  A number of
   vendors have implemented various solutions to this.  As examples of
   what has been done, for many years (long pre-dating cellular
   handsets) the technique described in [FINGER-HACK] has been
   supported.  Today, a number of email vendors include facilities to
   send SMS or other simple non-stream messages to clients on handsets
   when new mail arrives.  The Open Mobile Alliance (OMA) has published
   a mechanism that uses WAP PUSH to send a basic message containing a
   URL [OMA-EMN].  The IETF is investigating ways to standardize
   enhanced functionality in this area.

   A "push email" user experience can be achieved using any number of
   techniques, ranging from always-on TCP connectivity to the server and
   the NOTIFY extension described above, to OMA EMN, or even a non-
   standard trigger message over SMS.  In any technique, the client
   learns of the existence of new mail, and decides to fetch information
   about it, some part of it, or all of it, and then presents this to
   the user.



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5.5.  Searching and View Filters

   Lemonade Message Stores MUST support the ESEARCH [IMAP-ESEARCH]
   extension.  The extension allows clients to efficiently find the
   first or last messages, find a count of matching messages, and obtain
   a list of matching messages in a considerably more compact
   representation.

   Lemonade Message Stores also provide a mechanism for clients to avoid
   handling an entire mailbox, instead accessing a view of the mailbox.
   This technique, common in many desktop clients as a client-side
   capability, is useful for constrained clients to minimize the
   quantity of messages and notification data.

   Lemonade Message Stores therefore MUST implement the CONTEXT=SEARCH,
   ESORT, and CONTEXT=SORT extensions defined in [IMAP-CONTEXT], as well
   as the SORT extension defined in [IMAP-SORT].

5.6.  Mailbox Handling

   Lemonade Message Stores MUST support the NAMESPACE [IMAP-NAMESPACE]
   extension.  The extension allows clients to discover shared mailboxes
   and mailboxes belonging to other users, and provide a normalized
   hierarchy view of the mailboxes available.

   Lemonade Message Stores MUST support the I18NLEVEL=<n> [IMAP-I18N]
   extension, with <n> having the value 1 or 2.  It adds support for
   non-English (internationalized) search and sort functions.  (Note
   that I18NLEVEL=2 implies support for I18NLEVEL=1, so a Lemonade-
   compliant client that makes use of this extension MUST recognize
   either one.)

5.7.  Forward without Download

   In order to optimize network usage for the typical case where message
   content is copied to, or sourced from, the IMAP store, Lemonade
   provides support for a suite of extensions collectively known as
   "forward without download", discussed in detail in Section 8.

   Lemonade Message Stores MUST support CATENATE [IMAP-CATENATE],
   UIDPLUS [IMAP-UIDPLUS], and URLAUTH [IMAP-URLAUTH].  Lemonade Message
   Stores MUST also support URL-PARTIAL as described in Section 5.7.1.

5.7.1.  Support for PARTIAL in CATENATE and URLAUTH

   [IMAP-URL] introduced a new syntactic element for referencing a byte
   range of a message/body part.  This is done using the ;PARTIAL=
   field.  If an IMAP server supports PARTIAL in IMAP URL used in



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   CATENATE and URLAUTH extensions, then it MUST advertise the URL-
   PARTIAL capability in both the CAPABILITY response and the equivalent
   response-code.

5.8.  Additional IMAP Extensions

   Lemonade Message Stores MUST support the LITERAL+ [IMAP-LITERAL+]
   extension.  The extension allows clients to save a round trip each
   time a non-synchronizing literal is sent.

   Lemonade Message Stores MUST also implement the SASL-IR
   [IMAP-SASL-IR] extension, which allows clients to save a round trip
   during authentication, potentially pipelining the entire
   authentication sequence.

   Lemonade-compliant IMAP servers MUST support IMAP over TLS [IMAP] as
   required by [IMAP].  As noted above in Section 5.3, servers SHOULD
   support the deflate compression algorithm for TLS, as specified in
   [TLS-COMP].

5.9.  Registration of $Forwarded IMAP Keyword

   The $Forwarded IMAP keyword is used by several IMAP clients to
   specify that the marked message was forwarded to another email
   address, embedded within or attached to a new message.  A mail client
   sets this keyword when it successfully forwards the message to
   another email address.  Typical usage of this keyword is to show a
   different (or additional) icon for a message that has been forwarded.
   Once set, the flag SHOULD NOT be cleared.

   Lemonade Message Stores MUST be able to store the $Forwarded keyword.
   They MUST preserve it on the COPY operation.  The servers MUST
   support the SEARCH KEYWORD $Forwarded.

5.10.  Registration of $SubmitPending and $Submitted IMAP Keywords

   The $SubmitPending IMAP keyword designates the message as awaiting to
   be submitted.  This keyword allows storing messages waiting to be
   submitted in the same mailbox where messages that were already
   submitted and/or are being edited are stored.  A mail client sets
   this keyword when it decides that the message needs to be sent out.
   When a client (it might be a different client from the one that
   decided that the message is pending submission) starts sending the
   message, it atomically (using "STORE (UNCHANGEDSINCE)") adds the
   $Submitted keyword.  Once submission is successful, the
   $SubmitPending keyword is atomically cleared.  The two keywords allow
   messages being actively submitted (messages that have both $Submitted
   and $SubmitPending keywords set) to be distinguished from messages



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   awaiting to be submitted, or from messages already submitted.  They
   also allow all messages that were supposed to be submitted to be
   found, if the client submitting them crashes or quits before
   submitting them.

   Lemonade Message Stores MUST be able to store the $SubmitPending and
   the $Submitted keyword.  Lemonade Message Stores MUST preserve them
   on the COPY operation.  The servers MUST support the SEARCH KEYWORD
   $SubmitPending and SEARCH KEYWORD $Submitted.

5.11.  Related IMAP Extensions

   Section 5.11 is non-normative.

   Server implementations targeting to fulfill OMA MEM requirements
   [OMA-MEM-REQ] should consider implementing the [IMAP-FILTERS], which
   provides a way to persist definition of virtual mailboxes on the
   server.  They should also consider implementing the METADATA-SERVER
   [METADATA] extension, which provides a way of storing user-defined
   data associated with a user account.

6.  Lemonade Message Delivery Agents

   Lemonade Message Delivery Agents MUST support the [SIEVE] filtering
   language at the point of delivery, allowing the user to control which
   messages are accepted, and where they are filed.

   Lemonade Message Delivery Agents MUST support the Sieve Vacation
   extension [SIEVE-VACATION], which allows the client to set up an
   auto-responder, typically to report being on vacation (thus the name
   of the Sieve extension).

   Lemonade Message Delivery Agents MUST support the Sieve Enotify
   extension [SIEVE-NOTIFY], which allows a Sieve script to generate
   notifications (such as XMPP, SIP, or email) about received messages.

   Lemonade Message Delivery Agents MUST support the Sieve Variables
   extension [SIEVE-VARIABLES], which adds support for variables to the
   Sieve scripting language.  This extension is typically used with
   Sieve Enotify or Vacation to customize responses/notifications.

   Lemonade Message Delivery Agents MUST support the Sieve Relational
   extension [SIEVE-RELATIONAL], which adds support for relational
   comparisons to the Sieve scripting language.  This extension is
   typically used together with Sieve Enotify.






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   Lemonade Message Delivery Agents MUST support the Sieve Imap4Flags
   extension [SIEVE-IMAP4FLAGS], which allows a Sieve script to set IMAP
   flags/keywords when delivering a message to a mailbox.  For example,
   this can be used to automatically mark certain messages as
   interesting, urgent, etc.

   Lemonade Message Delivery Agents MUST support the i;unicode-casemap
   comparator in Sieve [UNICODE-CASEMAP], which is declared as
   "comparator-i;unicode-casemap" in the Sieve "require" statement.  The
   comparator allows for case-insensitive matching of Unicode
   characters.

   Lemonade Message Delivery Agents should consider supporting Sieve
   script management using the [MANAGESIEVE] protocol.  If they do, they
   MUST also advertise in [MANAGESIEVE] all Sieve extensions listed in
   this section.

7.  Lemonade Message User Agents

   Although all existing IMAP MUAs are Lemonade compliant in as much as
   all Lemonade services are based on the existing [IMAP] and [SUBMIT]
   protocols, client implementors are encouraged to take full advantage
   of the facilities provided by Lemonade Submission Servers and
   Lemonade Message Stores, as described in 4 and 5, respectively.

   When opening a connection to the Submission Server, clients MUST do
   so using port 587 unless explicitly configured to use an alternate
   port [RFC5068].  (Note that this requirement is somewhat stronger
   than the one specified in [SUBMIT], as [SUBMIT] didn't prescribe the
   exact procedure to be used by submission clients.)  If the TCP
   connection to the submission server fails to open using port 587, the
   client MAY then immediately retry using a different port, such as 25.
   See [SUBMIT] for information on why using port 25 is likely to fail
   depending on the current location of the client, and may result in a
   failure code during the SMTP transaction.

   In addition, some specifications are useful to support interoperable
   messaging with an enhanced user experience.

   Lemonade-capable clients SHOULD support the Format and DelSp
   parameters to the text/plain media type described in [FLOWED], and
   generate this format for messages.

   Lemonade-capable clients SHOULD support, and use, the $Forwarded
   keyword described in Section 5.9.






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8.  Forward without Download

8.1.  Motivations

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

   Lemonade "forward without download" makes use of the [SMTP-BURL]
   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.

   Lemonade "forward without download" has the advantage of maintaining
   one submission protocol, and thus avoids the risk of having multiple
   parallel and possibly divergent mechanisms for submission.  The
   client can use [SUBMIT] extensions without these being added to IMAP.
   Furthermore, by keeping the details of message submission in the SMTP
   SUBMIT server, Lemonade "forward without download" can work with
   other message retrieval protocols such as POP, NNTP, or whatever else
   may be designed in the future.

8.2.  Message Sending Overview

   The act of sending an email message can be 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 in the MUA.
   Frequently, users choose to save more complex messages on an [IMAP]
   server (via the APPEND command with the \Draft flag) for later recall
   by the MUA and resumption of the editing process.

   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 [ESMTP] infrastructure, typically using the [SUBMIT]
   protocol.









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8.3.  Traditional Strategy

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

   There is often no clear boundary between the editing and assembly
   processes.  If a message is forwarded, its content is often retrieved
   immediately and inserted into the message text.  Similarly, when
   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 retrieval of
   the draft transmits that entire (possibly large) content, as does
   message submission.

   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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8.4.  A New Strategy

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

        +--------------------+               +--------------+
        |                    | <------------ |              |
        |     MUA (M)        |               | IMAPv4Rev1   |
        |                    |               |  Server      |
        |                    | ------------> | (Server I)   |
        +--------------------+               +--------------+
               ^    |                              ^     |
               |    |                              |     |
               |    |                              |     |
               |    |                              |     |
               |    |                              |     |
               |    |                              |     |
               |    |                              |     v
               |    |                        +--------------+
               |    |----------------------> |   SMTP       |
               |                             |   Submit     |
               |-----------------------------|   Server     |
                                             |  (Server S)  |
                                             +--------------+

   Figure 1: Lemonade "forward without download"

   Lemonade "forward without download" allows a Message User Agent to
   compose and forward an email combining fragments that are located in
   an IMAP server, without having to download these fragments to the
   client.

   This section informatively describes two ways to perform "forward
   without download" based on where the message assembly takes place.
   The first uses the extended APPEND command [IMAP-CATENATE] to edit a
   draft message in the message store and cause the message assembly on
   the IMAP server.  This is most often used when a copy of the message
   is to be retained on the IMAP server, as discussed in Section 8.6.

   The second uses a succession of BURL and BDAT commands to submit and
   assemble through concatenation, message data from the client and
   external data fetched from the provided URL.  The two subsequent
   sections provide step-by-step instructions on how "forward without
   download" is achieved.






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8.4.1.  Message Assembly Using IMAP CATENATE Extension

   In the [SMTP-BURL]/[IMAP-CATENATE] variant of the Lemonade "forward
   without download" strategy, messages are initially composed and
   edited within an MUA.  The [IMAP-CATENATE] extension to [IMAP] is
   then used to create the messages on the IMAP server by transmitting
   new text and assembling them.  The UIDPLUS [IMAP-UIDPLUS] IMAP
   extension is used by the client in order to learn the UID of the
   created messages.  Finally, an [IMAP-URLAUTH] format URL is given to
   a [SUBMIT] server for submission using the BURL [SMTP-BURL]
   extension.

   The flow involved to support such a use case consists of:

   M: {to I -- Optional} The client connects to the IMAP server,
   optionally starts TLS (if data confidentiality is required),
   authenticates, opens a mailbox ("INBOX" in the example below), and
   fetches body structures (see [IMAP]).

   Example:

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

   M: {to I} The client invokes CATENATE (see [IMAP-CATENATE] for
   details of the semantics and steps) -- this allows the MUA to create
   messages on the IMAP server using new data combined with one or more
   message parts already present on the IMAP server.

   Note that the example for this step doesn't use the LITERAL+
   [IMAP-LITERAL+] extension.  Without LITERAL+ the new message is
   constructed using three round trips.  If LITERAL+ is used, the new
   message can be constructed using one round trip.












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        M: A0052 APPEND Sent FLAGS (\Draft \Seen $MDNSent)
            CATENATE (TEXT {475}
        I: + Ready for literal data
        M: Message-ID: <419399E1.6000505@caernarfon.example.org>
        M: Date: Thu, 12 Nov 2004 16:57:05 +0000
        M: From: Bob Ar <bar@example.org>
        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:
        M: --------------030308070208000400050907
        M: Content-Type: text/plain; format=flowed
        M:
        M: Our travel agent has sent the updated schedule.
        M:
        M: Cheers,
        M: Bob
        M: --------------030308070208000400050907
        M:  URL "/INBOX;UIDVALIDITY=385759045/;
           UID=25627/;Section=2.MIME" URL "/INBOX;
           UIDVALIDITY=385759045/;UID=25627/;Section=2" TEXT {44}
        I: + Ready for literal data
        M:
        M: --------------030308070208000400050907--
        M: )
        I: A0052 OK [APPENDUID 387899045 45] CATENATE Completed

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

        M: A0053 GENURLAUTH "imap://bob.ar@example.org/Sent;
           UIDVALIDITY=387899045/;uid=45;expire=2005-10-
           28T23:59:59Z;urlauth=submit+bob.ar" INTERNAL
        I: * GENURLAUTH "imap://bob.ar@example.org/Sent;
           UIDVALIDITY=387899045/;uid=45;expire=
           2005-10-28T23:59:59Z;urlauth=submit+bob.ar:
           internal:91354a473744909de610943775f92038"
        I: A0053 OK GENURLAUTH completed

   M: {to S} The client connects to the mail 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
   [IMAP-URLAUTH] for details of the semantics and steps -- this allows



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   the MUA to authorize the SMTP submit server to access the message
   composed as a result of the CATENATE step).  Note that the second
   EHLO command is required after a successful STARTTLS command.  Also
   note that there might be a third required EHLO command if the second
   EHLO response doesn't list any BURL options.  Section 8.4.2
   demonstrates this.

        S: 220 owlry.example.org ESMTP
        M: EHLO potter.example.org
        S: 250-owlry.example.com
        S: 250-8BITMIME
        S: 250-BINARYMIME
        S: 250-PIPELINING
        S: 250-BURL imap
        S: 250-CHUNKING
        S: 250-AUTH PLAIN
        S: 250-DSN
        S: 250-SIZE 10240000
        S: 250-STARTTLS
        S: 250 ENHANCEDSTATUSCODES
        M: STARTTLS
        S: 220 Ready to start TLS
        ...TLS negotiation, subsequent data is encrypted...
        M: EHLO potter.example.org
        S: 250-owlry.example.com
        S: 250-8BITMIME
        S: 250-BINARYMIME
        S: 250-PIPELINING
        S: 250-BURL imap
        S: 250-CHUNKING
        S: 250-AUTH PLAIN
        S: 250-DSN
        S: 250-SIZE 10240000
        S: 250 ENHANCEDSTATUSCODES
        M: AUTH PLAIN aGFycnkAaGFycnkAYWNjaW8=
        M: MAIL FROM:<bob.ar@example.org>
        M: RCPT TO:<foo@example.net>
        S: 235 2.7.0 PLAIN authentication successful.
        S: 250 2.5.0 Address Ok.
        S: 250 2.1.5 foo@example.net OK.
        M: BURL imap://bob.ar@example.org/Sent;UIDVALIDITY=387899045/;
           uid=45/;urlauth=submit+bar:internal:
           91354a473744909de610943775f92038 LAST

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



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

   The mail Submission Server opens an IMAP connection to the IMAP
   server:

        I: * OK [CAPABILITY IMAP4REV1 STARTTLS NAMESPACE LITERAL+
            CATENATE URLAUTH UIDPLUS CONDSTORE IDLE] imap.example.com
            IMAP server ready
        S: a000 STARTTLS
        I: a000 Start TLS negotiation now
        ...TLS negotiation, if successful - subsequent data
           is encrypted...
        S: a001 LOGIN submitserver secret
        I: a001 OK submitserver logged in
        S: a002 URLFETCH "imap://bob.ar@example.org/Sent;
           UIDVALIDITY=387899045/;uid=45/;urlauth=submit+bob.ar:
           internal:91354a473744909de610943775f92038"
        I: * URLFETCH "imap://bob.ar@example.org/Sent;
           UIDVALIDITY=387899045/;uid=45/;urlauth=submit+bob.ar:
           internal:91354a473744909de610943775f92038" {15065}
        ...message body follows...
        I: a002 OK URLFETCH completed
        S: a003 LOGOUT
        I: * BYE See you later
        I: a003 OK Logout successful

   Note that if data confidentiality is not required, the mail
   Submission Server may omit the STARTTLS command before issuing the
   LOGIN command.

   S: {to M} Submission server assembles the complete message; if the
   assembly succeeds, it returns OK to the MUA:

        S: 250 2.5.0 Ok.

   M: {to I} The client marks the message containing the forwarded
   attachment on the IMAP server.

        M: A0054 UID STORE 25627 +FLAGS.SILENT ($Forwarded)
        I: * 215 FETCH (UID 25627 MODSEQ (12121231000))
        I: A0054 OK STORE completed

   Note: the UID STORE command shown above will only work if the marked
   message is in the currently selected mailbox; otherwise, it requires
   a SELECT.  This command can be omitted, as it simply changes non-
   operational metadata not essential to client operations or




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   interoperability.  The untagged FETCH response is due to
   [IMAP-CONDSTORE].  The $Forwarded IMAP keyword is described in
   Section 5.9.

8.4.2.  Message Assembly Using SMTP CHUNKING and BURL Extensions

   In the [IMAP-URLAUTH]/[SMTP-BURL] variant of the Lemonade "forward
   without download" strategy, messages are initially composed and
   edited within an MUA.  During submission [SUBMIT], BURL [SMTP-BURL]
   and BDAT [SMTP-BINARYMIME] commands are used to create the messages
   from multiple parts.  New body parts are supplied using BDAT
   commands, while existing body parts are referenced using
   [IMAP-URLAUTH] format URLs in BURL commands.

   The flow involved to support such a use case consists of:
   M: {to I -- Optional} The client connects to the IMAP server,
   optionally starts TLS (if data confidentiality is required),
   authenticates, opens a mailbox ("INBOX" in the example below), and
   fetches body structures (see [IMAP]).

   Example:

           M: B0051 UID FETCH 25627 (UID BODYSTRUCTURE)
           I: * 161 FETCH (UID 25627 BODYSTRUCTURE (("TEXT" "PLAIN"
              ("CHARSET" "US-ASCII") NIL NIL "7BIT" 1152 23)(
              "TEXT" "PLAIN" ("CHARSET" "US-ASCII" "NAME"
              "trip.txt")
              "<960723163407.20117h@washington.example.com>"
              "Your trip details" "BASE64" 4554 73) "MIXED"))
           I: B0051 OK completed

   M: {to I} The client uses the GENURLAUTH command to request URLAUTH
   URLs (see [IMAP-URLAUTH]) referencing pieces of the message to be
   assembled.
   I: {to M} The IMAP server returns URLAUTH URLs suitable for later
   retrieval with URLFETCH (see [IMAP-URLAUTH] for details of the
   semantics and steps).














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        M: B0052 GENURLAUTH "imap://bob.ar@example.org/INBOX;
           UIDVALIDITY=385759045/;UID=25627/;Section=2.MIME;
           expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar"
           INTERNAL "imap://bob.ar@example.org/INBOX;
           UIDVALIDITY=385759045/;UID=25627/;Section=2;
           expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar" INTERNAL
        I: * GENURLAUTH "imap://bob.ar@example.org/INBOX;
           UIDVALIDITY=385759045/;UID=25627/;Section=2.MIME;
           expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar:
           internal:A0DEAD473744909de610943775f9BEEF"
           "imap://bob.ar@example.org/INBOX;
           UIDVALIDITY=385759045/;UID=25627/;Section=2;
           expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar:
           internal:BEEFA0DEAD473744909de610943775f9"
        I: B0052 OK GENURLAUTH completed

   M: {to S} The client connects to the mail Submission Server and
   starts a new mail transaction.  It uses BURL to instruct the SMTP
   submit server to fetch from the IMAP server pieces of the message to
   be sent (see [SMTP-BURL] for details of the semantics and steps).

   Note that the second EHLO command is required after a successful
   STARTTLS command.  The third EHLO command is required if and only if
   the second EHLO response doesn't list any BURL options.  See
   Section 8.4.1 for an example of submission where the third EHLO
   command/response is not present.

        S: 220 owlry.example.org ESMTP
        M: EHLO potter.example.org
        S: 250-owlry.example.com
        S: 250-8BITMIME
        S: 250-BINARYMIME
        S: 250-PIPELINING
        S: 250-BURL
        S: 250-CHUNKING
        S: 250-AUTH DIGEST-MD5
        S: 250-DSN
        S: 250-SIZE 10240000
        S: 250-STARTTLS
        S: 250 ENHANCEDSTATUSCODES
        M: STARTTLS
        S: 220 Ready to start TLS
        ...TLS negotiation, subsequent data is encrypted...
        M: EHLO potter.example.org
        S: 250-owlry.example.com
        S: 250-8BITMIME
        S: 250-BINARYMIME
        S: 250-PIPELINING



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        S: 250-BURL
        S: 250-CHUNKING
        S: 250-AUTH DIGEST-MD5 CRAM-MD5 PLAIN EXTERNAL
        S: 250-DSN
        S: 250-SIZE 10240000
        S: 250 ENHANCEDSTATUSCODES
        M: AUTH PLAIN aGFycnkAaGFycnkAYWNjaW8=
        S: 235 2.7.0 PLAIN authentication successful.
        M: EHLO potter.example.org
        S: 250-owlry.example.com
        S: 250-8BITMIME
        S: 250-BINARYMIME
        S: 250-PIPELINING
        S: 250-BURL imap imap://imap.example.org
        S: 250-CHUNKING
        S: 250-AUTH DIGEST-MD5 CRAM-MD5 PLAIN EXTERNAL
        S: 250-DSN
        S: 250-SIZE 10240000
        S: 250 ENHANCEDSTATUSCODES
        M: MAIL FROM:<bob.ar@example.org> BODY=BINARY
        S: 250 2.5.0 Address Ok.
        M: RCPT TO:<foo@example.net>
        S: 250 2.1.5 foo@example.net OK.
        M: BDAT 475
        M: Message-ID: <419399E1.6000505@caernarfon.example.org>
        M: Date: Thu, 12 Nov 2004 16:57:05 +0000
        M: From: Bob Ar <bar@example.org>
        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:
        M: --------------030308070208000400050907
        M: Content-Type: text/plain; format=flowed
        M:
        M: Our travel agent has sent the updated schedule.
        M:
        M: Cheers,
        M: Bob
        M: --------------030308070208000400050907
        S: 250 2.5.0 OK
        M: BURL imap://bob.ar@example.org/INBOX;
           UIDVALIDITY=385759045/;UID=25627/;Section=2.MIME;
           expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar:
           internal:A0DEAD473744909de610943775f9BEEF
        S: 250 2.5.0 OK
        M: BURL imap://bob.ar@example.org/INBOX;



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           UIDVALIDITY=385759045/;UID=25627/;Section=2;
           expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar:
           internal:BEEFA0DEAD473744909de610943775f9
        S: 250 2.5.0 OK
        M: BDAT 44 LAST
        M:
        M: --------------030308070208000400050907--

   S: {to I} The mail Submission Server uses URLFETCH to fetch the
   pieces of the message to be sent.  (See [SMTP-BURL] for details of
   the semantics and steps.  The so-called "pawn-ticket" authorization
   mechanism uses a URI which contains its own authorization
   credentials.).
   I: {to S} Returns the requested body parts.

   The mail Submission Server opens an IMAP connection to the IMAP
   server:

        I: * OK [CAPABILITY IMAP4REV1 STARTTLS NAMESPACE LITERAL+
            CATENATE URLAUTH UIDPLUS CONDSTORE IDLE] imap.example.com
            IMAP server ready
        S: b000 STARTTLS
        I: b000 Start TLS negotiation now
        ...TLS negotiation, if successful - subsequent data
           is encrypted...
        S: b001 LOGIN submitserver secret
        I: b001 OK submitserver logged in
        S: b002 URLFETCH "imap://bob.ar@example.org/INBOX;
           UIDVALIDITY=385759045/;UID=25627/;Section=2.MIME;
           expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar:
           internal:A0DEAD473744909de610943775f9BEEF" "imap://
           bob.ar@example.org/INBOX;
           UIDVALIDITY=385759045/;UID=25627/;Section=2;
           expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar:
           internal:BEEFA0DEAD473744909de610943775f9"
        I: * URLFETCH "imap://bob.ar@example.org/INBOX;
           UIDVALIDITY=385759045/;UID=25627/;Section=2.MIME;
           expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar:
           internal:A0DEAD473744909de610943775f9BEEF" {84}
        ...message section follows...
            "imap://bob.ar@example.org/INBOX;
           UIDVALIDITY=385759045/;UID=25627/;Section=2;
           expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar:
           internal:BEEFA0DEAD473744909de610943775f9" {15065}
        ...message section follows...
        I: b002 OK URLFETCH completed
        S: b003 LOGOUT
        I: * BYE See you later



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        I: b003 OK Logout successful

   Note that if data confidentiality is not required, the mail
   Submission Server may omit the STARTTLS command before issuing the
   LOGIN command.

   S: {to M} Submission Server assembles the complete message; if the
   assembly succeeds, it acknowledges acceptance of the message by
   sending 250 response to the last BDAT command:

        S: 250 2.5.0 Ok, message accepted.

   M: {to I} The client marks the message containing the forwarded
   attachment on the IMAP server.

        M: B0053 UID STORE 25627 +FLAGS.SILENT ($Forwarded)
        I: * 215 FETCH (UID 25627 MODSEQ (12121231000))
        I: B0053 OK STORE completed

   Note: the UID STORE command shown above will only work if the marked
   message is in the currently selected mailbox; otherwise, it requires
   a SELECT.  As in the previous example, this command is not critical,
   and can be omitted.  The untagged FETCH response is due to
   [IMAP-CONDSTORE].  The $Forwarded IMAP keyword is described in
   Section 5.9.

8.5.  Security Considerations for Pawn-Tickets

   The so-called "pawn-ticket" authorization mechanism uses a URI, which
   contains its own authorization credentials using [IMAP-URLAUTH].  The
   advantage of this mechanism is that the SMTP submit [SUBMIT] server
   cannot access any data on the [IMAP-URLAUTH] server without a "pawn-
   ticket" created by the client.

   The "pawn-ticket" grants access only to the specific data that the
   SMTP submit [SUBMIT] server is authorized to access, can be revoked
   by the client, and can have a time-limited validity.

8.6.  Copies of Sent Messages: The fcc Problem

   The "fcc problem" refers to delivering a copy of a message to a
   mailbox, or "file carbon copy".  By far, the most common case of fcc
   is a client leaving a copy of outgoing mail in a "Sent Mail" 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



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   APPEND to a mailbox on an IMAP server.  The latter is one of the
   "repetitive network data transmissions" that represents the "problem"
   aspect of the "fcc problem".

   The BURL [SMTP-BURL] extension can be used to eliminate the
   additional transmission.  The final message is uploaded to the
   mailbox designed for outgoing mail by the APPEND command of [IMAP].
   Note that when doing so, the client ought to use the $SubmitPending
   and $Submitted IMAP keywords described in Section 5.10.  Also note
   that APPEND, including when enhanced by [IMAP-CATENATE], can only
   create a single copy of the message and this is only of use on the
   server that stages the outgoing message for submission.  Additional
   copies of the message on the same server can be created by using one
   or more COPY commands.

9.  Deployment Considerations

   Deployment considerations are discussed extensively in
   [LEMONADE-DEPLOYMENTS].

10.  Security Considerations

   Implementors are advised to examine the security considerations of
   all the referenced documents.  This section merely highlights these,
   and advises implementors on specific issues relating to the
   combination of extensions.

   Security considerations on Lemonade "forward without download" are
   discussed throughout Section 8.  Additional security considerations
   can be found in [IMAP], [SUBMIT], [SIEVE], and other documents
   describing other SMTP, IMAP, and Sieve extension comprising the
   Lemonade Profile.

   Note that the mandatory-to-implement authentication mechanism for
   SMTP submission is described in [SMTP-AUTH].  The mandatory-to-
   implement authentication mechanism for IMAP is described in [IMAP].

10.1.  Confidentiality Protection of Submitted Messages

   When clients submit new messages, link protection such as [TLS]
   guards against an eavesdropper seeing the contents of the submitted
   message.  It is worth noting, however, that even if TLS is not used,
   the security risks are no worse if BURL is used to reference the text
   than if the text is submitted directly.  If BURL is not used, an
   eavesdropper gains access to the full text of the message.  If BURL
   is used, the eavesdropper may or may not be able to gain such access,





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   depending on the form of BURL used.  For example, some forms restrict
   use of the URL to an entity authorized as a Submission Server or a
   specific user.

10.2.  TLS

   When Lemonade clients use the BURL extension for mail submission, an
   extension that requires sending a URLAUTH token to the mail
   Submission Server, such a token should be protected from interception
   to avoid a replay attack that may disclose the contents of the
   message to an attacker.  [TLS]-based encryption of both the IMAP
   session that issues GENURLAUTH and the mail submission path will
   provide protection against this attack.

   Lemonade-compliant mail Submission Servers SHOULD use TLS-protected
   IMAP connections when fetching message content using the URLAUTH
   token provided by the Lemonade client.

   When a client uses SMTP STARTTLS to send a BURL command that
   references non-public information, there is a user expectation that
   the entire message content will be treated confidentially.  To meet
   this expectation, the message Submission Server SHOULD use STARTTLS
   or a mechanism providing equivalent data confidentiality when
   fetching the content referenced by that URL.

10.3.  Additional Extensions and Deployment Models

   This specification provides no additional security measures beyond
   those in the referenced Internet Mail and Lemonade documents.

   We note, however, the security risks associated with:

   o  Outband notifications

   o  Server configuration by client

   o  Client configuration by server

   o  Presence of proxy servers

   o  Presence of servers as intermediaries

   o  In general, the deployment models considered by OMA MEM that are
      not conventional IETF deployment models

   o  Measures to address a perceived need to traverse firewalls and
      mobile network intermediaries




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   Deployments that provide these additional services or operate in
   these environments need to consult the security considerations for
   the relevant standards and organizational security practices.

11.  IANA Considerations

   IMAP4 capabilities are registered by IETF Review, as defined in
   [RFC5226].  This document defines the URL-PARTIAL IMAP capability
   (Section 5.7.1).  IANA added this extension to the IANA IMAP
   Capability registry.

12.  Changes since RFC 4550

   When compared to RFC 4550, this document adds the following
   additional requirements on a Lemonade compliant IMAP server:

   IMAP extensions:  BINARY, COMPRESS=DEFLATE, CONTEXT=SEARCH,
      CONTEXT=SORT, CONVERT, ENABLE, ESEARCH, ESORT, I18NLEVEL=1,
      NOTIFY, QRESYNC, SASL-IR, SORT, URL-PARTIAL;

   IMAP keywords:  $SubmitPending, $Submitted.

   Other requirements:  Require any Lemonade compliant IMAP server to
      support the CAPABILITY response code.

   When compared to RFC 4550, this document adds the following new
   requirements on a Lemonade compliant Message Delivery Agents:

   Support for the Sieve filtering language, together with the following
   Sieve extensions:

   ENOTIFY, IMAP4FLAGS, RELATIONAL, VACATION, VARIABLES, comparator-
   i;unicode-casemap.

   When compared to RFC 4550, this document recommends use of the
   DEFLATE compression method for TLS.  All other requirements remain
   the same.

   Additionally, the following changes/improvments were done to RFC 4550
   (the list might be incomplete):

      A new section with some additional requirements on Lemonade Mail
      User Agents was added, in particular they are required to support
      Format=flowed parameter to the text/plain media type.

      Usage of the $Forwarded IMAP keyword was clarified.

      Forward-without-download examples were corrected and extended.



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      Added a new section describing in-band and out-of-band
      notifications from a Lemonade compliant mailstore.

13.  Acknowledgements

   The editors acknowledge and appreciate the work and comments of the
   IETF Lemonade working group and the OMA MEM working group.

   In particular, the editors would like to thank Eric Burger, Glenn
   Parsons, Randall Gellens, Filip Navara, Zoltan Ordogh, Greg
   Vaudreuil, and Fan Xiaohui for their comments and reviews.

14.  References

14.1.  Normative References

   [FLOWED]   Gellens, R., "The Text/Plain Format and DelSp Parameters",
              RFC 3676, February 2004.

   [IMAP]     Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, March 2003.

   [IMAP-BINARY]
              Nerenberg, L., "IMAP4 Binary Content Extension", RFC 3516,
              April 2003.

   [IMAP-CATENATE]
              Resnick, P., "Internet Message Access Protocol (IMAP)
              CATENATE Extension", RFC 4469, April 2006.

   [IMAP-COMPRESS]
              Gulbrandsen, A., "The IMAP COMPRESS Extension", RFC 4978,
              August 2007.

   [IMAP-CONDSTORE]
              Melnikov, A. and S. Hole, "IMAP Extension for Conditional
              STORE Operation or Quick Flag Changes Resynchronization",
              RFC 4551, June 2006.

   [IMAP-CONTEXT]
              Cridland, D. and C. King, "Contexts for IMAP4", RFC 5267,
              July 2008.

   [IMAP-CONVERT]
              Melnikov, A. and P. Coates, "Internet Message Access
              Protocol - CONVERT Extension", RFC 5259, July 2008.





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   [IMAP-ENABLE]
              Gulbrandsen, A. and A. Melnikov, "The IMAP ENABLE
              Extension", RFC 5161, March 2008.

   [IMAP-ESEARCH]
              Melnikov, A. and D. Cridland, "IMAP4 Extension to SEARCH
              Command for Controlling What Kind of Information Is
              Returned", RFC 4731, November 2006.

   [IMAP-I18N]
              Newman, C., Gulbrandsen, A., and A. Melnikov, "Internet
              Message Access Protocol Internationalization", RFC 5255,
              June 2008.

   [IMAP-IDLE]
              Leiba, B., "IMAP4 IDLE command", RFC 2177, June 1997.

   [IMAP-LITERAL+]
              Myers, J., "IMAP4 non-synchronizing literals", RFC 2088,
              January 1997.

   [IMAP-NAMESPACE]
              Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342,
              May 1998.

   [IMAP-NOTIFY]
              Gulbrandsen, A., King, C., and A. Melnikov, "The IMAP
              NOTIFY Extension", RFC 5465, February 2009.

   [IMAP-QRESYNC]
              Melnikov, A., Cridland, D., and C. Wilson, "IMAP4
              Extensions for Quick Mailbox Resynchronization", RFC 5162,
              March 2008.

   [IMAP-SASL-IR]
              Siemborski, R. and A. Gulbrandsen, "IMAP Extension for
              Simple Authentication and Security Layer (SASL) Initial
              Client Response", RFC 4959, September 2007.

   [IMAP-SORT]
              Crispin, M. and K. Murchison, "Internet Message Access
              Protocol - SORT and THREAD Extensions", RFC 5256,
              June 2008.

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




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   [IMAP-URL]
              Melnikov, A. and C. Newman, "IMAP URL Scheme", RFC 5092,
              November 2007.

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

   [KEYWORDS]
              Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

   [SIEVE-IMAP4FLAGS]
              Melnikov, A., "Sieve Email Filtering: Imap4flags
              Extension", RFC 5232, January 2008.

   [SIEVE-NOTIFY]
              Melnikov, A., Leiba, B., Segmuller, W., and T. Martin,
              "Sieve Email Filtering: Extension for Notifications",
              RFC 5435, January 2009.

   [SIEVE-RELATIONAL]
              Segmuller, W. and B. Leiba, "Sieve Email Filtering:
              Relational Extension", RFC 5231, January 2008.

   [SIEVE-VACATION]
              Showalter, T. and N. Freed, "Sieve Email Filtering:
              Vacation Extension", RFC 5230, January 2008.

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

   [SMTP-8BITMIME]
              Klensin, J., Freed, N., Rose, M., Stefferud, E., and D.
              Crocker, "SMTP Service Extension for 8bit-MIMEtransport",
              RFC 1652, July 1994.

   [SMTP-AUTH]
              Siemborski, R. and A. Melnikov, "SMTP Service Extension
              for Authentication", RFC 4954, July 2007.







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   [SMTP-BINARYMIME]
              Vaudreuil, G., "SMTP Service Extensions for Transmission
              of Large and Binary MIME Messages", RFC 3030,
              December 2000.

   [SMTP-BURL]
              Newman, C., "Message Submission BURL Extension", RFC 4468,
              May 2006.

   [SMTP-DSN]
              Moore, K., "Simple Mail Transfer Protocol (SMTP) Service
              Extension for Delivery Status Notifications (DSNs)",
              RFC 3461, January 2003.

   [SMTP-PIPELINING]
              Freed, N., "SMTP Service Extension for Command
              Pipelining", STD 60, RFC 2920, September 2000.

   [SMTP-SIZE]
              Klensin, J., Freed, N., and K. Moore, "SMTP Service
              Extension for Message Size Declaration", STD 10, RFC 1870,
              November 1995.

   [SMTP-STATUSCODES]
              Freed, N., "SMTP Service Extension for Returning Enhanced
              Error Codes", RFC 2034, October 1996.

   [SMTP-TLS]
              Hoffman, P., "SMTP Service Extension for Secure SMTP over
              the Transport Layer Security", RFC 3207, February 2002.

   [SUBMIT]   Gellens, R. and J. Klensin, "Message Submission for Mail",
              RFC 4409, April 2006.

   [TLS]      Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [TLS-COMP]
              Hollenbeck, S., "Transport Layer Security Protocol
              Compression Methods", RFC 3749, May 2004.

   [UNICODE-CASEMAP]
              Crispin, M., "i;unicode-casemap - Simple Unicode Collation
              Algorithm", RFC 5051, October 2007.







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14.2.  Informative References

   [ESMTP]    Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              October 2008.

   [Err1807]  RFC Errata, Errata ID 1807, RFC 5162,
              <http://www.rfc-editor.org>.

   [Err1808]  RFC Errata, Errata ID 1808, RFC 5162,
              <http://www.rfc-editor.org>.

   [Err1809]  RFC Errata, Errata ID 1809, RFC 5162,
              <http://www.rfc-editor.org>.

   [Err1810]  RFC Errata, Errata ID 1810, RFC 5162,
              <http://www.rfc-editor.org>.

   [FINGER-HACK]
              Gellens, R., "Simple New Mail Notification", RFC 4146,
              August 2005.

   [IMAP-FILTERS]
              Melnikov, A. and C. King, "IMAP4 Extension for Named
              Searches (Filters)", RFC 5466, February 2009.

   [IMAP-SYNC-HOWTO]
              Melnikov, A., "Synchronization Operations for Disconnected
              IMAP4 Clients", RFC 4549, June 2006.

   [LEMONADE-ARCH]
              Burger, E. and G. Parsons, "LEMONADE Architecture -
              Supporting Open Mobile Alliance (OMA) Mobile Email (MEM)
              Using Internet Mail", RFC 5442, March 2009.

   [LEMONADE-DEPLOYMENTS]
              Gellens, R., "Deployment Considerations for Lemonade-
              Compliant Mobile Email", BCP 143, RFC 5383, October 2008.

   [LEMONADE-NOTIFICATIONS]
              Gellens, R., Ed., "Lemonade Notifications Architecture",
              RFC 5551, August 2009.

   [MANAGESIEVE]
              Melnikov, A. and T. Martin, "A Protocol for Remotely
              Managing Sieve Scripts", Work in Progress, September 2008.






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   [METADATA]
              Daboo, C., "The IMAP METADATA Extension", RFC 5464,
              February 2009.

   [OMA-EMN]  Open Mobile Alliance, "Open Mobile Alliance Email
              Notification Version 1.0", OMA http://
              www.openmobilealliance.org/Technical/release_program/
              emn_v10.aspx, October 2007.

   [OMA-MEM-ARCH]
              Open Mobile Alliance, "Mobile Email Architecture
              Document", OMA (Work in Progress),
              http://www.openmobilealliance.org/, October 2005.

   [OMA-MEM-REQ]
              Open Mobile Alliance, "Mobile Email Requirements
              Document", OMA http://www.openmobilealliance.org/
              release_program/docs/RD/
              OMA-RD-MobileEmail-V1_0_20051018-C.pdf, Oct 2005.

   [RFC5068]  Hutzler, C., Crocker, D., Resnick, P., Allman, E., and T.
              Finch, "Email Submission Operations: Access and
              Accountability Requirements", BCP 134, RFC 5068,
              November 2007.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5598]  Crocker, D., "Internet Mail Architecture", RFC 5598,
              July 2009.




















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Appendix A.  Errata

   Errata ID: 1807 [Err1807]

   Status: Verified
   Type: Technical

   Reported By: Timo Sirainen
   Date Reported: 2009-07-14
   Verifier Name: Alexey Melnikov
   Date Verified: 2009-07-18

   Section 1 says:

   It should say:

   Once a "CONDSTORE enabling command" is issued by the client, the
   server MUST automatically include both UID and mod-sequence data in
   all subsequent untagged FETCH responses (until the connection is
   closed), whether they were caused by a regular STORE/UID STORE, a
   STORE/UID STORE with UNCHANGEDSINCE modifier, or an external agent.
   Note that this rule doesn't affect untagged FETCH responses caused by
   a FETCH command that doesn't include UID and/or MODSEQ FETCH data
   item, or UID FETCH without the MODSEQ FETCH data item.

   Notes:

   Rationale:

   It's very difficult for clients to make use of unsolicited FETCH
   responses without the UID field. This is made even worse by the text
   that says "servers SHOULD NOT send UIDs for previously expunged
   messages [in VANISHED replies]". Since it's not a MUST NOT, a
   conversation with an RFC compliant server could be for example:

   A1 NOOP
   * 0 EXISTS
   A1 OK
   A2 NOOP
   * 10 EXISTS
   * VANISHED 1000:2000
   * 3 FETCH (FLAGS (\Seen) MODSEQ (14749))
   * 5 FETCH (FLAGS (\Seen) MODSEQ (14749))
   * VANISHED 2000:3000
   A2 OK NOOP Completed

   The client couldn't do anything with the information from FETCH
   replies, because it can't know what messages they refer to.



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  Errata ID: 1808 [Err1808]

  Status: Verified
  Type: Technical

  Reported By: Timo Sirainen
  Date Reported: 2009-07-14
  Verifier Name: Alexey Melnikov
  Date Verified: 2009-07-18

  Section 3.4 says:

  If at least one message got expunged, the server MUST send
  the updated per-mailbox modification
  sequence using the HIGHESTMODSEQ response code (defined in
  [CONDSTORE]) in the tagged OK response.

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

  It should say:

  The server MUST NOT send the updated per-mailbox modification
  sequence using the HIGHESTMODSEQ response code (defined in
  [CONDSTORE]) in the tagged OK response, as this might cause loss of
  synchronization on the client.

  Example:    C: A202 CLOSE
              S: A202 OK done

  Notes:

  Rationale:

  The HIGHESTMODSEQ can't be used reliably unless server sends to client
  all changes done by other clients. Even then it's difficult for both
  clients and servers to implement this. For example:

  C1: 2 STORE 1 +FLAGS.SILENT \Deleted
  S1: * 1 FETCH (MODSEQ 1)
  S1: 2 OK

  C2: 1 STORE 2 +FLAGS.SILENT \Deleted
  S1: * 2 FETCH (MODSEQ 2)
  S2: 1 OK

  C1: 3 CLOSE
  S1: 3 [HIGHESTMODSEQ 3]



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  The client probably thought that only message 1 was expunged, so it
  doesn't register the second expunge. And it probably never will if it
  uses QRESYNC to find out only about new expunges.

  And even worse example would be if the second client had also removed
  the \Deleted flag from message 1. Then the first client would have
  registered wrong message to be expunged.


  Errata ID: 1809 [Err1809]

  Status: Verified
  Type: Technical

  Reported By: Timo Sirainen
  Date Reported: 2009-07-14
  Verifier Name: Alexey Melnikov
  Date Verified: 2009-07-18

  Section 5 says:

  After completing a full synchronization, the client MUST also take
  note of any unsolicited MODSEQ FETCH data items received from the
  server.  Whenever the client receives a tagged response to a command,
  it calculates the highest value among all MODSEQ FETCH data items
  received since the last tagged response.  If this value is bigger
  than the client's copy of the HIGHESTMODSEQ value, then the client
  MUST use this value as its new HIGHESTMODSEQ value.

  Note: It is not safe to update the client's copy of the HIGHESTMODSEQ
  value with a MODSEQ FETCH data item value as soon as it is received
  because servers are not required to send MODSEQ FETCH data items in
  increasing modseqence order.  This can lead to the client missing
  some changes in case of connectivity loss.

  It should say:

  After completing a full synchronization, the client MUST also take
  note of any unsolicited MODSEQ FETCH data items and HIGHESTMODSEQ
  response codes received from the server.  Whenever the client receives
  a tagged response to a command, it checks the received unsolicited
  responses to calculate the new HIGHESTMODSEQ value.  If the
  HIGHESTMODSEQ response code is received, the client MUST use it even
  if it has seen higher mod-sequences.  Otherwise, the client calculates
  the highest value among all MODSEQ FETCH data items received since the
  last tagged response.  If this value is bigger than the client's copy
  of the HIGHESTMODSEQ value, then the client MUST use this value as its
  new HIGHESTMODSEQ value.



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  Example:    C: A1 STORE 1:2 (UNCHANGEDSINCE 96) +FLAGS.SILENT \Seen
              S: * 1 FETCH (UID 6 MODSEQ (103))
              S: * 2 FETCH (UID 7 MODSEQ (101))
              S: * OK [HIGHESTMODSEQ 99] VANISHED reply with
                        MODSEQ 100 is delayed
              S: A1 OK [MODIFIED 3] done

              C: A2 STORE 3 +FLAGS.SILENT \Seen
              S: * 3 FETCH (UID 8 MODSEQ (104))
              S: A2 OK [HIGHESTMODSEQ 99] Still delaying VANISHED

              C: A3 NOOP
              S: * VANISHED 8
              S: A3 OK [HIGHESTMODSEQ 104] done

  Note: It is not safe to update the client's copy of the HIGHESTMODSEQ
  value with a MODSEQ FETCH data item value as soon as it is received
  because servers are not required to send MODSEQ FETCH data items in
  increasing modseqence order.  Some commands may also delay EXPUNGE
  (or VANISHED) replies with smaller mod-sequences. These can lead to
  the client missing some changes in case of connectivity loss.

  Notes:

  Rationale:

  Otherwise clients could lose changes in case of connectivity loss.

  Errata ID: 1810 [Err1810]

  Status: Verified
  Type: Technical

  Reported By: Timo Sirainen
  Date Reported: 2009-07-14
  Verifier Name: Alexey Melnikov
  Date Verified: 2009-07-18

  Section 1 says:

  It should say:

  Server implementing QRESYNC MUST send untagged events to client in a
  way that client doesn't lose any changes in case of connectivity loss.
  In particular this means that if server sends MODSEQ FETCH data items
  while EXPUNGE (or VANISHED) replies with lower mod-sequences are being
  delayed, the server MUST send HIGHESTMODSEQ response code with a lower
  value than the EXPUNGE's mod-sequence. See example in section 5.



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  Notes:

  This is related to the other errata in section 5, which describes what
  the client's behavior should be. This describes what the server's
  behavior should be. Would have been nice to put them into the same
  section, but that probably would require larger changes.

Authors' Addresses

   Dave Cridland (editor)
   Isode Limited
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   EMail: dave.cridland@isode.com


   Alexey Melnikov (editor)
   Isode Limited
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   EMail: Alexey.Melnikov@isode.com


   Stephane H. Maes (editor)
   Oracle
   MS 4op634, 500 Oracle Parkway
   Redwood Shores, CA  94539
   USA

   Phone: +1-203-300-7786
   EMail: stephane.maes@oracle.com














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