Network Working Group C. Newman
Internet-Draft Sun Microsystems
Expires: August 10, 2004 February 10, 2004
Message Submission with Composition
draft-newman-lemonade-compose-01.txt
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Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
The submission profile of Simple Mail Transfer Protocol (SMTP)
provides a standard way for an email client to submit a complete
message for delivery. The chunking extension provides a way for a
client to compose a message for submission from a series of client
provided pieces. This specification further extends the chunking
facility so that a client can compose a message from additional
sources. For example, a client could use this facility to forward a
message from an IMAP server or forward a web page as an attachment to
a new message.
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Table of Contents
1. Conventions Used in this Document . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. BURL Submission Extension . . . . . . . . . . . . . . . . . . 3
3.1 SMTP Submission Extension Registration . . . . . . . . . . . . 3
3.2 Composition Transaction . . . . . . . . . . . . . . . . . . . 4
3.3 Supported URIs . . . . . . . . . . . . . . . . . . . . . . . . 4
3.4 Transfer Encoding Conversion . . . . . . . . . . . . . . . . . 5
3.5 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.6 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Message Submission with Composition for Small Devices . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Changes from -00 . . . . . . . . . . . . . . . . . . . . . . . 7
Normative References . . . . . . . . . . . . . . . . . . . . . 8
Informative References . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . 10
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1. Conventions Used in this Document
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
in this document are to be interpreted as defined in "Key words for
use in RFCs to Indicate Requirement Levels" [5].
The formal syntax use the Augmented Backus-Naur Form (ABNF) [6]
notation including the core rules defined in Appendix A of RFC 2234.
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively. If a single "C:" or "S:" label applies to
multiple lines, then the line breaks between those lines are for
editorial clarity only and are not part of the actual protocol
exchange.
2. Introduction
This specification defines an extension to the standard Message
Submission [8] protocol to permit composition of messages from
multiple sources on the Internet. This extends the CHUNKING [12]
mechanism so that chunks of the message can come from external
sources. This provides the ability to forward a web page or email
message without first downloading it to the client.
3. BURL Submission Extension
This section defines the BURL submission extension.
3.1 SMTP Submission Extension Registration
1. The name of this submission extension is "BURL". This extends
the Message Submission protocol on port 587 and MUST NOT be
advertised by a regular SMTP [11] server on port 25. Compliant
submission clients MUST attempt to use port 587 prior to falling
back to port 25, unless explicitly configured to do otherwise by
the user.
2. The EHLO keyword value associated with the extension is "BURL".
3. The BURL EHLO keyword will have zero or more arguments. Each
argument is either an absoluteURI [7], a prefix of an absoluteURI
including the <authority> component or a URI scheme name. The
arguments which appear after BURL may change subsequent to the
use of SMTP AUTH [9].
4. This extension adds the BURL SMTP verb. This verb is only
permitted between the first BDAT [12] SMTP verb in a message
transaction and a subsequent BDAT in the same transaction which
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includes an end marker. Out of sequence use of the BURL SMTP
verb will result in a "503 5.5.1 Bad Sequence of commands" error.
A server which advertises both BURL and PIPELINING [22] MUST
accept an entire transaction including MAIL FROM, one or more
RCPT TO and a combination of BDAT and BURL commands in one round
trip. If no valid recipients are present, the BDAT commands all
fail and the data is consumed, and the BURL commands also fail
without triggering a fetch of the URL.
5. This extension adds no new parameters to the MAIL or RCPT verbs.
6. The BURL verb is used during a CHUNKING SMTP transaction. If the
argument is a valid URL which the submit server can resolve to a
data object, the submit server will resolve the URL and
optionally apply a content-transfer-encoding.
3.2 Composition Transaction
When a composition client connects to a composition server, it will
first authenticate (using SMTP AUTH and perhaps STARTTLS), and then
can compose and submit any number of messages with full
interoperability with important SMTP extensions such as delivery
status notifications [14]. Each message which is composed and
submitted is called a message composition transaction.
A message composition transaction will typically consist of a MAIL
FROM, one or more RCPT TO headers, an initial BDAT, an optional
series of BURL or BDAT commands, and a BURL or BDAT command with the
"LAST" tag. The client is permitted to pipeline [22] the entire
transaction in one round-trip. However, it MUST wait for the results
of the "LAST" BDAT or BURL command prior to initiating a new
transaction.
The BURL command directs the server to fetch the data object to which
the URL refers, perform any necessary content transfer encoding
conversions on that object and include it in the message. If the URL
fetch or conversion fails, the server will either fail the entire
transaction (including consuming any subsequent BDAT or BURL commands
in the pipeline) or retry the composition later based on the value of
the "failhow" argument to BURL.
3.3 Supported URIs
The BURL EHLO keyword arguments list the types of URIs the
composition server can resolve. If it lists just the scheme name,
that indicates the server supports all forms of that URI which refer
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to a single data object. In the case of IMAP URLs [20], advertising
the bare scheme name indicates the server also supports the URLAUTH
[23] extended form.
The composition server can indicate a pre-arranged trust relationship
with another server by including a URL qualified by the server name.
For example, if user "joe" authenticates to the composition server
and subsequent to authentication the server advertises "imap://
joe@example.com", that indicates the composition server has a trust
relationship with example.com that permits access to all messages
that joe can access.
If the EHLO keyword has an absoluteURI argument, that indicates the
server has authorized access to all URIs with that absoluteURI as a
prefix.
Implementations are encouraged to support both IMAP and HTTP [21]
URLs at a minimum.
3.4 Transfer Encoding Conversion
The composition client can specify that the server should perform a
transfer encoding conversion after resolving the URL.
o The "base64" conversion indicates that if the data was already
base64 encoded, it should be left unchanged. Otherwise, any
content transfer encoding is removed and the result is base64
encoded.
o The "8bit" conversion indicates that any content transfer encoding
is removed, lines longer than 998 characters MUST be wrapped onto
multiple lines by insertion of a CRLF, NUL octets MUST be dropped,
and bare newline or bare carriage return MUST be converted to
CRLF.
o The "none" conversion indicates that the data is unchanged and any
original content transfer encoding is left in place. If the
server does not advertise BINARYMIME and if the raw data would
require any changes to be labelled "8bit", then the server MUST
fail the BURL command.
o The "binary" conversion is only permitted if the BINARYMIME EHLO
keyword was advertised, and indicates any content transfer
encoding is to be removed and the data is to be included otherwise
unaltered.
The composition server MAY fail any BURL command which results in
insertion of data that would violate the MIME charset or
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content-transfer-encoding label at that location in the message. The
composition server MUST fail the BURL command if data with the high
bit set is included prior to the first blank line in the message.
3.5 Example
TBD.
3.6 Formal Syntax
The following syntax specification inherits ABNF [6] and Uniform
Resource Identifiers [7].
burl-param = scheme / absoluteURI / trusted-domain
; parameter to BURL EHLO keyword
burl-cmd = "BURL" SP conversion SP failhow
SP absoluteURI [SP end-marker] CRLF
conversion = "base64" / "8bit" / "binary" / "none"
failhow = "now" / "retry"
end-marker = "LAST"
trusted-domain = scheme "://" authority
4. Message Submission with Composition for Small Devices
A Message Submission [8] server is considered to be a compliant
Message Submission with Composition server if it implements the
following specifications:
o BURL (Section 3): Mandatory
o DSN [14]: Mandatory
o STARTTLS [13]: Mandatory
o CHUNKING [12]: Mandatory
o BINARYMIME [12]: Mandatory
o PIPELINING [22]: Mandatory
o Revised SMTP [11]: Mandatory, with exceptions in [8].
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o SMTP AUTH [9]: Mandatory
o Submission [8]: Mandatory
o Error Codes [3]: Recommended
o Size [2]: Mandatory
o 521 [18]: MUST NOT
o Checkpoint [17]: Optional
o 8BITMIME [1]: Mandatory
o TURN [16]: MUST NOT
Specifications which help reduce data transmissions or round-trips
between a small device and the composition server are mandatory, as
well as SMTP extensions proven in the installed base. A Message
Composition server MUST require SMTP AUTH prior to accepting a
submission. The SASL PLAIN [10] mechanism in combination with
STARTTLS [13] is the mandatory-to-implement authentication mechanism.
5. IANA Considerations
When this is published as an RFC, the "BURL" SMTP extension as
described in Section 3 will be registered. This registration will be
marked as for use by message submission [8] only in the registry.
6. Security Considerations
Implementations which support the URLAUTH [23] form of IMAP URLs MUST
implement both the SMTP STARTTLS [13] and the IMAP STARTTLS [15]
extensions and MUST have a configuration setting which requires their
use with such IMAP URLs.
When a client uses the SMTP STARTTLS to send a BURL command which
references non-public information, the message submission server MUST
use STARTTLS or a mechanism providing equivalent data privacy when
resolving that URL.
7. Changes from -00
o Added the end-marker "LAST", so this could be used without BDAT
and works with a pre-composed message.
o Changed "Message Composition" to "Message Submission with
Composition" in several places.
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o Correct Spelling Errors
Normative References
[1] Klensin, J., Freed, N., Rose, M., Stefferud, E. and D. Crocker,
"SMTP Service Extension for 8bit-MIMEtransport", RFC 1652, July
1994.
[2] Klensin, J., Freed, N. and K. Moore, "SMTP Service Extension
for Message Size Declaration", STD 10, RFC 1870, November 1995.
[3] Freed, N., "SMTP Service Extension for Returning Enhanced Error
Codes", RFC 2034, October 1996.
[4] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[6] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[7] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
[8] Gellens, R. and J. Klensin, "Message Submission", RFC 2476,
December 1998.
[9] Myers, J., "SMTP Service Extension for Authentication", RFC
2554, March 1999.
[10] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC 2595,
June 1999.
[11] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April
2001.
[12] Vaudreuil, G., "SMTP Service Extensions for Transmission of
Large and Binary MIME Messages", RFC 3030, December 2000.
[13] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, February 2002.
[14] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service
Extension for Delivery Status Notifications (DSNs)", RFC 3461,
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January 2003.
[15] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
Informative References
[16] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
August 1982.
[17] Crocker, D. and N. Freed, "SMTP Service Extension for
Checkpoint/Restart", RFC 1845, September 1995.
[18] Durand, A. and F. Dupont, "SMTP 521 Reply Code", RFC 1846,
September 1995.
[19] De Winter, J., "SMTP Service Extension for Remote Message Queue
Starting", RFC 1985, August 1996.
[20] Newman, C., "IMAP URL Scheme", RFC 2192, September 1997.
[21] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[22] Freed, N., "SMTP Service Extension for Command Pipelining", STD
60, RFC 2920, September 2000.
[23] Crispin, M., "Internet Message Access Protocol (IMAP) -
URLAUTH", draft-crispin-imap-urlauth-00 (work in progress),
June 2003.
Author's Address
Chris Newman
Sun Microsystems
1050 Lakes Drive
West Covina, CA 91790
US
EMail: chris.newman@sun.com
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