<Lemonade Profile> February 2005
Lemonade
Internet Draft: Lemonade Profile S. H. Maes
Document: draft-ietf-lemonade-profile-01.txt A. Melnikov
Expires: August 2005 February 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-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document describes the Lemonade profile to allow clients to
submit new email messages incorporating content which resides on
locations external to the client ("forward without download").
The Lemonade profile relies upon extensions to other protocols;
specifically URLAUTH, CATENATE, Lemonade Command Extensions in the
IMAP protocol [RFC 3501] and BURL in the SUBMIT protocol [RFC 2476].
In addition, the Lemonade profile contains Lemonade Command
extensions for quick reconnect and media conversion.
Conventions used in this document
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In examples, "M:", "I:" and "S:" indicate lines sent by the client
messaging user agent, IMAP e-mail server and 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 [RFC2119].
Table of Contents
Status of this Memo...............................................1
Abstract..........................................................1
Conventions used in this document.................................1
Table of Contents.................................................2
1. Introduction...................................................2
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..................................4
2.5. Additional Considerations.................................8
2.6. The fcc problem...........................................8
3. Media Conversion...............................................9
3.1. Introduction..............................................9
3.2. Static media conversion...................................9
3.3. Conversion of streamed media..............................9
3.4. Quick Reconnect scheme....................................9
4. Future work...................................................10
Security Considerations..........................................10
References.......................................................10
Version History..................................................12
Acknowledgments..................................................12
Authors Addresses................................................12
Intellectual Property Statement..................................12
Full Copyright Statement.........................................13
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
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- 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. This is
an onerous burden for clients operating over low-bandwidth and/or
high-latency links.
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
SUBMIT servers.
Pull has the distinct 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 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 and/or time-consuming
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.
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]
protocol.
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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
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.
2.4.
Step by step description
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The model distinguishes between a Messaging User Agent (MUA), an
IMAPv4Rev1 Server ([RFC3501]) and a submit server ([RFC2476]), as
illustrated in Figure 1.
+--------------------+ +--------------+
| | <------------ | |
| MUA (M) | | IMAPv4 Rev1 |
| | | Server |
| | ------------> | (Server I) |
+--------------------+ +--------------+
^ | ^ |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | v
| | +--------------+
| |------------------------->| |
| | 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])
Example:
M: A0051 FETCH 161 (UID BODYSTRUCTURE)
I: * 161 FETCH (UID 25627 BODYSTRUCTURE (("TEXT" "PLAIN"
("CHARSET" "US-ASCII") NIL
NIL "7BIT" 1152 23)("TEXT" "PLAIN" ("CHARSET" "US-ASCII"
"NAME"
"cc.diff")
"<960723163407.20117h@washington.example.net>" "Compiler
diff"
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"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 $MDNSent) TEXT {738}
I: + Ready for literal data
M: Return-Path: <bar@example.org>
M: Received: from [127.0.0.2]
M: by rufus.example.org via TCP (internal) with
ESMTPA;
M: Thu, 11 Nov 2004 16:57:07 +0000
M: Message-ID: <419399E1.6000505@example.org>
M: Date: Thu, 12 Nov 2004 16:57:05 +0000
M: From: Bob Ar <bar@example.org>
M: X-Accept-Language: en-us, en
M: MIME-Version: 1.0
M: To: foo@example.net
M: Subject: About our holiday trip
M: Content-Type: multipart/mixed;
M: boundary="------------030308070208000400050907"
M:
M: --------------030308070208000400050907
M: Content-Type: text/plain; charset=us-ascii; format=flowed
M: Content-Transfer-Encoding: 7bit
M:
M: Our travel agent has sent the updated schedule.
M:
M: Cheers,
M: Bob
M: --------------030308070208000400050907
M: URL "imap://imap.example.org/INBOX;UIDVALIDITY=385759045/;
UID=25627;Section=1.2" TEXT {44}
I: + Ready for literal data
M: --------------030308070208000400050907--
M:
I: A0052 OK [APPENDUID 387899045 45] CATENATE Completed
M: A0053 UID STORE XXX +FLAGS.SILENT ($Forwarded)
I: A0053 OK STORE completed
<< EditorÆs note: Recommend UIDPLUS extension û especially useful
when appending messages to a non-selected mailbox>>
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M: {to I} The client uses GENURLAUTH command to request and
URLAUTH URL (See [URLAUTH]).
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
"imap://bob.ar@example.org/Sent;UIDVALIDITY=387899045/;uid=45/;urla
uth=submit+bar" INTERNAL
I: * GENURLAUTH
"imap://bob.ar@example.org/Sent;UIDVALIDITY=387899045/;uid=45/;urla
uth=submit+bar:internal:91354a473744909de610943775f92038"
I: A0054 OK GENURLAUTH completed
M: {to S} The client connects to the submission server and starts
a new mail transaction. It uses BURL to let the 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 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
S: 250 ENHANCEDSTATUSCODES
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
imap://bob.ar@example.org/Sent;UIDVALIDITY=387899045/;uid=45/;urlau
th=submit+bar:internal:91354a473744909de610943775f92038 LAST
S: {to I} The 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.).
I: {to S} Provides the message composed as a result of the
CATENATE step).
Submission server opens IMAP connection to the IMAP server:
I: * OK [CAPABILITY IMAP4REV1 URLAUTH] example.com IMAP
server ready
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S: a001 LOGIN submitserver secret
I: a001 OK submitserver logged in
S: a002 URLFETCH "
imap://bob.ar@example.org/Sent;UIDVALIDITY=387899045/;uid=45/;urlau
th=submit+bar:internal:91354a473744909de610943775f92038"
I: * URLFETCH "
imap://bob.ar@example.org/Sent;UIDVALIDITY=387899045/;uid=45/;urlau
th=submit+bar:internal:91354a473744909de610943775f92038" {15065}
...message body follows...
S: a002 OK URLFETCH completed
<< EditorÆs note: The submission server may LOGOUT>>
S2: {to M} OK (2XX)
Submission server returns OK to the MUA:
S: 250 2.5.0 Ok.
The messaging user agent, mail server and submit server MUST support
IMAPv4 Rev1 [RFC3501], CATENATE [CATENATE] and URLAUTH [URLAUTH].
2.5.
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 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 submit [RFC2476] server is authorized to
access, can be revoked by the client, and can have a time-limited
validity.
2.6.
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:
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(1a) there is one, and only one, fcc destination on a single
server
(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.
Media Conversion
3.1.
Introduction
<<EditorÆs note: To be done when agreed by WG>>
3.2.
Static media conversion
<<EditorÆs note: To be done when agreed by WG>>
3.3.
Conversion of streamed media
<<EditorÆs note: To be done when agreed by WG>>
3.4.
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>>
S: * OK [CAPABILITY IMAP4REV1 STARTTLS AUTH=LOGIN CONDSTORE
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
20010715194045000
41,43:211,214:541)
S: + VXNlciBOYW1lAA==
C: dGVzdDg=
S: + UGFzc3dvcmQA
C: dGVzdDg=
S: * FOLDER INBOX
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))
S: b0002 OK [CAPABILITY IMAP4REV1 IDLE NAMESPACE MAILBOX-REFERRALS
SCAN
SORT THREAD=REFERENCES THREAD=ORDEREDSUBJECT MULTIAPPEND] User
test8 authenticated
4.
Future work
Future versions of the Lemonade profile are expected to address
issues related to access of email form mobile devices, possibly
including:
- transport optimization for low or costly bandwidth and less
reliable mobile networks
- server to client notifications outside of the traditional IMAP
band
- dealing with firewall and intermediaries
- compression
- filtering
Security Considerations
Security considerations on the Lemonade Pull Model are discussed
throughout section 2.
<< EditorÆs note: TBD (Reconnect, etc.)>>
References
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[IMAP-DISC] Melnikov, A. "Synchronization Operations For
Disconnected Imap4 Clients", IMAP-DISC, work in progress, draft-
melnikov-imap-disc-XX.txt
[RFC2119] Brader, S. "Keywords for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
http://www.ietf.org/rfc/rfc2119
[RFC2180] Gahrns, M. "IMAP4 Multi-Accessed Mailbox Practice", RFC
2180, July 1997.
http://www.ietf.org/rfc/rfc2180
[RFC2234] Crocker, D. and Overell, P. "Augmented BNF for Syntax
Specifications", RFC 2234, Nov 1997.
http://www.ietf.org/rfc/rfc2234
[RFC2683] Leiba, B. "IMAP4 Implementation Recommendations", RFC 2683
Sep 1999.
http://www.ietf.org/rfc/rfc2683
[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.
http://www.ietf.org/rfc/rfc3501
[RFC2476] Gellens, R. and Klensin, J., "Message Submission", RFC
2476, December 1998.
[CATENATE]Resnick, P., "Internet Message Access Protocol (IMAP)
CATENATE Extension", draft-ietf-lemonade-catenate-XX, (work in
progress).
[BURL] Newman, C., "Message Composition", draft-ietf-lemonade-
burl-xx (work in progress).
[URLAUTH] Crispin, M. and Newman, C., "Internet Message Access
Protocol (IMAP) - URLAUTH Extension", draft-ietf-lemonade-urlauth-
XX.txt, (work in progress).
[POSTADDRESS] Melnikov, A., "IMAP4 POSTADDRESS extension", work in
progress, draft-melnikov-imap-postaddress-XX.txt
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[RECONNECT] Melnikov, A. and C. Wilson, " IMAP4 extension for quick
reconnect ", work in progress, draft-ietf-lemonade-reconnect-
XX.txt
Version History
[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 ôCoprirightö.
Acknowledgments
This document is based on the work in progress described in draft-
crispin-lemonade-pull-xx.txt.
Authors Addresses
Stephane H. Maes
Oracle Corporation
500 Oracle Parkway
M/S 4op634
Redwood Shores, CA 94065
USA
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
UK
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
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
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rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Full Copyright Statement
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