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[lemonade] draft-fanf-smtp-quickstart-00
The attached draft is to be discussed at the Prague meeting.
I submitted it before the -00 cutoff but it was rejected: they said
> Please read carefully the instructions at
> http://www.ietf.org/ietf/1id-guidelines.html. Make sure that you give to
> your draft proper file name and resubmit.
I've had no luck getting an explanation of what they don't like about
the filename, and they now seem to be ignoring my messages to
ietf-action at ietf.org, so I've given up trying to get the draft published
properly.
Tony.
--
f.a.n.finch <dot at dotat.at> http://dotat.at/
VIKING:: SOUTHWEST, BACKING SOUTH FOR A TIME, 4 OR 5 INCREASING 6 TO GALE 8,
PERHAPS SEVERE GALE 9 LATER. MODERATE OR ROUGH BECOMING VERY ROUGH. RAIN OR
SHOWERS. MODERATE OR GOOD..
SMTP T. Finch
Internet-Draft University of Cambridge
Intended status: Standards Track February 24, 2007
Expires: August 28, 2007
The QUICKSTART SMTP service extension
draft-fanf-smtp-quickstart-00
Status of this Memo
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 becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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The list of current Internet-Drafts can be accessed at
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The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on August 28, 2007.
Copyright Notice
Copyright (C) The IETF Trust (2007).
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Abstract
This memo specifies modifications to SMTP's start-up sequence which
reduce the number of round trips between the client and the server
before message transmission starts. This can significantly reduce
the delay for interactive message submission over slow links.
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Document revision
$Cambridge: hermes/doc/qsmtp/draft-fanf-smtp-quickstart.xml,v 1.20
2007/02/24 10:50:04 fanf2 Exp $
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. QUICKSTART SMTP service extension definition . . . . . . . . . 6
4. Extended server greeting . . . . . . . . . . . . . . . . . . . 7
5. The QHLO command . . . . . . . . . . . . . . . . . . . . . . . 8
6. The QTLS command . . . . . . . . . . . . . . . . . . . . . . . 9
7. Changes to the AUTH command . . . . . . . . . . . . . . . . . 11
8. Issuing commands early . . . . . . . . . . . . . . . . . . . . 12
9. Changes to the STARTTLS command . . . . . . . . . . . . . . . 14
10. Backwards compatibility . . . . . . . . . . . . . . . . . . . 15
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
12. Security considerations . . . . . . . . . . . . . . . . . . . 17
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
13.1. Normative references . . . . . . . . . . . . . . . . . . 18
13.2. Informative references . . . . . . . . . . . . . . . . . 18
Appendix A. Example round trip summaries . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 27
Intellectual Property and Copyright Statements . . . . . . . . . . 28
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1. Introduction
The start of an SMTP connection is not currently optimized to reduce
the number of round trips between the client and server. This is a
particular problem for message submission over slow links, where the
resulting delay can easily be more than a second. The QUICKSTART
SMTP service extension introduces some changes which eliminate round
trips and therefore reduce the delay before messages can be
transmitted. The key features of the extension are:
o Earlier announcement of the list of SMTP service extensions
supported by the server.
o The QHLO and QTLS commands, which are quicker replacements for the
EHLO and STARTTLS commands.
o The ability to pipeline the STARTTLS and AUTH commands.
o A mechanism to allow the client to issue commands without always
having to wait for the server's extension list.
Each of these features has advantages by itself, and they can be used
together to provide greater improvements. QUICKSTART is designed
with two profiles in mind: the basic profile uses the QHLO and QTLS
commands and the pipelined AUTH command to bring the first MAIL
command forward from the client's 9th packet to the 5th; the full
profile uses the <qhlo-id> and pipelined STARTTLS to bring it as
early as the 3rd. Appendix A illustrates these counts in more
detail.
Although SMTP QUICKSTART is probably most useful in conjunction with
message submission [RFC4409], it MAY also be used with MTA-to-MTA
SMTP - though attention should be paid to the security considerations
in Section 12.
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2. Terminology
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].
The metalinguistic notation used in this memo corresponds to the
"Augmented BNF" used in other Internet mail system memos. The reader
who is not familiar with that syntax should consult the ABNF
specification [RFC4234]. Rules not defined in this specification are
either defined in the ABNF core rules or in [RFC2821]. Metalanguage
terms used in running text are surrounded by pointed brackets (e.g.,
<list-id>) for clarity.
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3. QUICKSTART SMTP service extension definition
The QUICKSTART SMTP service extension is defined as follows:
o The name of the service extension is "QUICKSTART".
o The EHLO keyword value associated with the extension is
"QUICKSTART".
o The QUICKSTART EHLO keyword value has four OPTIONAL parameters
("QTLS", "AUTH", "QHLO=<qhlo-id>", and "STARTTLS") to which more
can be added by future specifications.
o The extension defines two additional commands: "QHLO" and "QTLS".
o There are no additional parameters to the MAIL or RCPT commands
defined by this extension and their maximum lengths are not
increased.
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4. Extended server greeting
An SMTP server that supports QUICKSTART MUST respond to the client's
connection with an extended greeting according to the syntax below.
This greeting has a similar format to the SMTP EHLO response, that
is, the first line is the same as an un-extended greeting, and
subsequent lines list the SMTP service extensions supported by the
server. The list MUST include the QUICKSTART keyword and SHOULD
include PIPELINING [RFC2920].
The extended greeting allows a client to find out the server's
supported extensions one round trip earlier than in normal SMTP.
Syntax:
qsmtp-greet = ( "220-" domain [ SP ehlo-greet ] CRLF
*( "220-" ehlo-line CRLF )
"220" SP ehlo-line CRLF )
ehlo-line =/ "QUICKSTART" *( SP qsmtp-param )
qsmtp-param = "QHLO=" qhlo-id / "QTLS" /
"AUTH" / "STARTTLS" /
esmtp-param
qhlo-id = esmtp-value
The QUICKSTART keyword MAY be followed by parameters that indicate
which OPTIONAL features of this specification are supported by the
server. Clients MUST ignore QUICKSTART parameters that they do not
understand. The following parameters are defined in this
specification:
o The "QTLS" parameter indicates that the server supports the QTLS
command specified in Section 6.
o The "AUTH" parameter indicates that the server supports pipelining
of the AUTH command as specified in Section 7.
o The "QHLO=<qhlo-id>" parameter indicates that the server allows
the client to issue commands before receiving the server's list of
supported extensions, as described in Section 8.
o The "STARTTLS" parameter indicates that the server supports
pipelining of the STARTTLS command as specified in Section 9.
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5. The QHLO command
The QHLO command has two forms. Support for the basic form defined
in this section is REQUIRED. The full form is OPTIONAL, and is
defined in Section 8.
An SMTP client that supports QUICKSTART MUST first ensure that the
server supports it by checking the server's greeting against the
syntax specified in Section 4. The client then issues QHLO as its
first command instead of EHLO. The basic form of QHLO has the same
semantics as the EHLO command, except that it MAY be pipelined if the
server also supports PIPELINING [RFC2920], and the server's 220
response to QHLO does not include its list of supported extensions.
The pipelined QHLO command allows a client to save one round trip by
not having to wait for the server's response before issuing further
commands.
Syntax:
qhlo = "QHLO" SP Domain CRLF
qhlo-ok-rsp = "220" SP domain [ SP ehlo-greet ] CRLF
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6. The QTLS command
Support for the QTLS command is OPTIONAL, and is indicated by the
presence of the QTLS parameter after the QUICKSTART keyword in the
list of extensions supported by the server. If the server supports
both STARTTLS [RFC3207] and QUICKSTART then it SHOULD also support
QTLS.
Syntax:
qtls = "QTLS" CRLF
The QTLS command has no parameters. After issuing the QTLS command,
the client immediately starts the TLS handshake. The server MUST NOT
issue an SMTP response to the QTLS command before the TLS handshake.
Therefore it is not possible for the server to report problems (as
with the 454 response to the STARTTLS command) except by closing the
connection - which it SHOULD NOT do. Instead, the server SHOULD
ensure that it can support TLS (e.g. by initializing its TLS library)
before listing the extensions it supports, rather than lazily in
reaction to a QTLS or STARTTLS command.
After the TLS handshake has been completed, the SMTP protocol is
reset to the state at the start of a connection, so the server
proceeds to issue a QUICKSTART extended 220 greeting <qsmtp-greet>.
If the server requires that the client performs a TLS negotiation
before it accepts any commands, then it SHOULD accept the QHLO and
QTLS commands before TLS negotiation, as well as the NOOP, EHLO,
STARTTLS, and QUIT commands specified in [RFC3207]
Apart from these differences, the QTLS command is the same as the
STARTTLS command, and the other requirements specified in [RFC3207]
apply.
The QTLS command saves one round trip before the TLS handshake by
omitting the server's response, and saves another after the TLS
handshake by announcing the list of extensions supported by the
server earlier than is typical with STARTTLS.
Clients will generally want to issue the QTLS command at the start of
a connection, immediately after the QHLO command. The most efficient
way of doing so is to pipeline QHLO, QTLS, and the TLS handshake, but
then it can be difficult to disentangle the server's response to QHLO
from its side of the TLS handshake. Therefore servers MUST allow
clients to issue the QTLS command without issuing QHLO or EHLO first,
though they MAY require that the client does not issue the QHLO
command before receiving the server's greeting. This is illustrated
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in Appendix A.
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7. Changes to the AUTH command
This section describes an OPTIONAL change to the behaviour of the
AUTH command [RFC2554], support for which is indicated by the
presence of the AUTH parameter after the QUICKSTART keyword in the
list of extensions supported by the server. This change is also
specified by [RFC4468], so if the server lists support for BURL and
QUICKSTART and PIPELINING then it MUST include the QUICKSTART AUTH
parameter.
If the client uses a SASL mechanism which can be completed in one
round trip, such as EXTERNAL [RFC4422] or PLAIN [RFC4616], then it
MAY pipeline the AUTH command. If the authentication fails, the
server SHOULD reject all subsequent commands other than AUTH, NOOP,
HELO, EHLO, QHLO, or QUIT with a "530 Authentication failure" reply.
If the server supports ENHANCEDSTATUSCODES [RFC2034] [RFC3463], the
status code to be returned SHOULD be 5.7.0.
This change allows another round trip to be saved.
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8. Issuing commands early
It is possible to save more round trips if the client can issue
commands before receiving the list of extensions supported by the
server. There are opportunities to do this at the very start of the
TCP connection, after the STARTTLS command [RFC3207], and after the
AUTH command negotiates a security layer [RFC2554]. These are called
"QUICKSTART points" in this section.
Support for this is OPTIONAL, and is indicated by the presence of the
"QHLO=<qhlo-id>" parameter after the QUICKSTART keyword in the list
of extensions supported by the server. The server MUST also support
PIPELINING [RFC2920].
The <qhlo-id> parameter value is a case-sensitive token which
identifies the list of service extensions and associated parameters
in which it was included. The server MUST state a different
<qhlo-id> for different lists of extensions or if any of their
parameters changes. This generally implies that the server will
state different <qhlo-id>s at different QUICKSTART points. For
example, if the server only supports AUTH PLAIN after TLS
negotiation, it will state a different <qhlo-id> in its responses to
EHLO before and after STARTTLS. If the server's SIZE parameter
[RFC1870] changes in response to available disk space, its <qhlo-id>
will change too. Section 12 includes some security considerations
for the <qhlo-id>.
The client uses the <qhlo-id> with the full form of the QHLO command.
Syntax:
qhlo =/ "QHLO" SP Domain SP qhlo-id CRLF
The <qhlo-id> in the client's QHLO command MUST match the <qhlo-id>
issued by the server in its <qsmtp-greet>, or the <qhlo-id> that the
server would have issued in its <ehlo-ok-rsp> response to an EHLO
command from the client. If the <qhlo-id> matches, the server SHOULD
respond with a <qhlo-ok-rsp> response. If the <qhlo-id> does not
match there are two possible responses: if the server has already
listed its supported service extensions (e.g. in a <qsmtp-greet>) it
responds with a "520 Please use the correct QHLO ID" response;
otherwise (e.g. after STARTTLS or AUTH) it responds with a <qhlo-
long-no>, which includes the list of extensions supported by the
server.
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Syntax:
qhlo-long-no = ( "521-" domain [ SP ehlo-greet ] CRLF
*( "521-" ehlo-line CRLF )
"521" SP ehlo-line CRLF )
If the server responds to QHLO with a 520 or 521 code, it SHOULD
reject subsequent commands other than NOOP, QHLO, or QUIT with "503
Bad sequence of commands" responses. If the server supports
ENHANCEDSTATUSCODES [RFC2034] [RFC3463], the status code to be
returned SHOULD be 5.5.1. The client SHOULD recover from this state
by issuing a QHLO command containing the correct <qhlo-id>.
The client MAY issue commands early at a QUICKSTART point if it has
previously connected to the server and the server included QUICKSTART
QHLO=<qhlo-id> in its list of supported extensions at that point.
The client's first command at the QUICKSTART point MUST be the full
form of QHLO. The client MUST have remembered the details of the
extensions that the client is interested in and which are supported
by the server at that point, including the <qhlo-id>. The client
MUST NOT confuse <qhlo-id>s obtained from different QUICKSTART
points. The client MUST NOT assume that the server's current
<qhlo-id> will be the same as on the previous connection, therefore
the client MUST be prepared for its QHLO being rejected. Note that
this implies that the client SHOULD NOT pipeline an early QHLO
command and a QTLS command, since the server cannot reject the QTLS
command except by closing the connection; instead it SHOULD use
STARTTLS as described in Section 9.
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9. Changes to the STARTTLS command
This section describes an OPTIONAL change to the behaviour of the
STARTTLS command [RFC3207] which is indicated by the presence of the
STARTTLS parameter after the QUICKSTART keyword in the list of
extensions supported by the server. If the server lists both the
QTLS and QHLO=<qhlo-id> parameters, then it SHOULD also list the
STARTTLS parameter.
The advantages of the QTLS command are that it allows the client to
initiate a TLS handshake faster without getting muddled by SMTP
responses from the server, and it allows the client to receive the
list of extensions supported by the server inside TLS sooner. When
the client uses the QHLO=<qhlo-id> feature to issue commands early,
it isn't possible to avoid interleaving SMTP responses with the TLS
handshake, and it is no longer necessary to get the server's list of
supported extensions. Furthermore, the QTLS command's lack of error
recovery becomes a problem. Therefore full QUICKSTART uses a
pipelined STARTTLS command.
If the server supports QUICKSTART STARTTLS, then the client MAY start
the TLS handshake immediately after issuing the STARTTLS command,
without waiting for the server's response to STARTTLS. If the server
wishes to reject the STARTTLS command, it MUST discard any pipelined
TLS client hello before issuing its response.
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10. Backwards compatibility
If the first command issued by the client is EHLO, then the server
MUST treat it as normal extended SMTP conversation as specified in
[RFC2821]. In this case the client MUST disregard the list of
extensions provided in the server's greeting. For example, if the
server lists PIPELINING in its greeting, the client MUST NOT assume
that PIPELINING will be listed in the server's response to EHLO.
If the first command issued by the client is not QTLS nor QHLO nor
EHLO, then the server MUST treat it as an un-extended SMTP
conversation as specified in [RFC0821].
In the above situations, the server MAY require that the client's
first command is issued after the client has received the greeting.
A client that issues commands early (as described in the two previous
sections) MUST be prepared to deal with errors that indicate the
server no longer supports QUICKSTART, such as 50X or 55X SMTP
responses [RFC2821], or 5.5.X, 5.3.X, or 5.7.X enhanced status codes
[RFC3463]. If the client issued a QTLS or pipelined STARTTLS
command, it SHOULD disconnect and re-try using ESMTP without
QUICKSTART; otherwise it MAY recover by issuing an EHLO command and
re-trying.
Similarly, a client that issues commands early MUST be prepared to
deal with a 421 or 4.3.2 "Service not available" error. In this
situation the client SHOULD disconnect and re-try some time later.
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11. IANA Considerations
This memo defines a new SMTP service extension keyword, "QUICKSTART"
in Section 3. Four parameters are initially defined for the keyword.
Further parameters MAY be defined by future specifications and MUST
conform to the <esmtp-param> syntax; parameter keywords starting with
X are for Private Use, and other parameter keywords SHOULD be
allocated according to the Specification Required policy [RFC2434].
IANA maintains a registry of "WITH protocol types" for use in the
"with" clause of the Received header trace fields in an Internet
message. Most of the contents of this registry are set out in
[RFC3848]. This specification updates the registry as follows:
o The new keyword "QSMTP" indicates that the client used the
QUICKSTART extension, that is, it used the QHLO command to start
the SMTP session instead of EHLO.
o The new keyword "QSMTPA" indicates that the client used QUICKSTART
with the SMTP AUTH [RFC2554] extension, and that it authenticated
successfully.
o The new keyword "QSMTPS" indicates that the client used
QUICKSTART, and that it successfully completed TLS negotiation to
provide a strong transport encryption layer by using the QTLS or
STARTTLS commands.
o The new keyword "QSMTPSA" indicates that the client used
QUICKSTART and both TLS and AUTH were successfully negotiated (the
combination of QSMTPS and QSMTPA).
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12. Security considerations
Like the EHLO command, the QHLO command includes a client host name
parameter for logging and tracing purposes. This can useful to
distinguish different clients behind a NAT, for example. However
clients commonly state an incorrect host name, so it SHOULD NOT be
relied on. SMTP servers SHOULD use all available client identifiers
for logging and tracing, such as its IP address, reverse DNS, TLS
certificate, and SMTP AUTH credentials.
It is increasingly popular for SMTP servers (especially MX hosts) to
use heuristics based on protocol conformance to identify abusive
clients and reject email from them. For example, the server can
delay its greeting and see if the client waits to receive it before
issuing commands. This heuristic can still be applied in the
presence of full support for QUICKSTART, by checking that the
client's early first command is not QHLO before deciding that it is
abusive.
The full QUICKSTART protocol requires the client to demonstrate that
it has previously communicated with the server, by echoing the
<qhlo-id>. This can be faked by abusive clients if the <qhlo-id> is
too easy to guess. The server can defend itself against pump-and-
dump abuse by making the <qhlo-id> depend on more than just the list
of supported extensions and their parameters: for example it might
use a digest of the list, the server and client IP addresses, and a
secret.
Of course, since QUICKSTART is most useful for interactive message
submission, and high latency is not such a problem for automated
message relay, MX hosts can simply elect not to support QUICKSTART.
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13. References
13.1. Normative references
[RFC0821] Postel, J., "Simple Mail Transfer Protocol", STD 10,
RFC 821, August 1982.
[RFC2034] Freed, N., "SMTP Service Extension for Returning Enhanced
Error Codes", RFC 2034, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC2554] Myers, J., "SMTP Service Extension for Authentication",
RFC 2554, March 1999.
[RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
April 2001.
[RFC2920] Freed, N., "SMTP Service Extension for Command
Pipelining", STD 60, RFC 2920, September 2000.
[RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, February 2002.
[RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes",
RFC 3463, January 2003.
[RFC3848] Newman, C., "ESMTP and LMTP Transmission Types
Registration", RFC 3848, July 2004.
[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
13.2. Informative references
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC1870] Klensin, J., Freed, N., and K. Moore, "SMTP Service
Extension for Message Size Declaration", STD 10, RFC 1870,
November 1995.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
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(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC4409] Gellens, R. and J. Klensin, "Message Submission for Mail",
RFC 4409, April 2006.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[RFC4468] Newman, C., "Message Submission BURL Extension", RFC 4468,
May 2006.
[RFC4616] Zeilenga, K., "The PLAIN Simple Authentication and
Security Layer (SASL) Mechanism", RFC 4616, August 2006.
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Appendix A. Example round trip summaries
In the following examples, a line prefixed with C: indicates the
start of a packet from the client to the server, and S: indicates one
from the server to the client. Subsequent lines without a prefix are
pipelined into the same packet. The C: or S: may be followed by a
protocol name - TCP, SMTP or TLS - which indicates a change in the
top-most protocol active in the connection. The rest of the line
describes a protocol element.
The following figure outlines the sequence of packets at the start of
a non-QUICKSTART message submission [RFC4409], including the TCP
handshake [RFC0793], starting ESMTP [RFC2821], securing it using
STARTTLS [RFC3207] [RFC4346], authenticating [RFC2554] [RFC4422]
[RFC4616], and starting to send the message using pipelining
[RFC2920]. The MAIL command appears in the 9th packet from the
client, and pipelining is not possible before this point.
C: TCP SYN
S: SYN/ACK
C: ACK
S: SMTP <greeting>
C: EHLO <domain>
S: <ehlo-ok-rsp>
C: STARTTLS
S: 220 OK
C: TLS client hello
S: server hello, certificate, etc.
C: key exchange, change cipher, finish handshake
S: change cipher, finish handshake
C: SMTP EHLO <domain>
S: <ehlo-ok-rsp>
C: AUTH PLAIN <creds>
S: 235 OK
C: MAIL FROM:<...>
RCPT TO:<...>
...
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The following shows the use of a pipelined QHLO command, but no other
QUICKSTART features. (It is not very realistic.) The MAIL command
is in the client's 8th packet.
C: TCP SYN
S: SYN/ACK
C: ACK
S: SMTP <qsmtp-greet>
C: QHLO <domain>
STARTTLS
S: 220 OK
220 OK
C: TLS client hello
S: server hello, certificate, etc.
C: key exchange, change cipher, finish handshake
S: change cipher, finish handshake
C: SMTP EHLO <domain>
S: <ehlo-ok-rsp>
C: AUTH PLAIN <creds>
S: 235 OK
C: MAIL FROM:<...>
RCPT TO:<...>
...
The following shows the use of the QTLS and QHLO commands, to
illustrate a basic QUICKSTART connection. The MAIL command is in the
client's 6th packet.
C: TCP SYN
S: SYN/ACK
C: ACK
S: SMTP <qsmtp-greet>
C: QTLS
TLS client hello
S: server hello, certificate, etc.
C: key exchange, change cipher, finish handshake
S: change cipher, finish handshake
SMTP <qsmtp-greet>
C: QHLO <domain>
AUTH PLAIN <creds>
S: 220 OK
235 OK
C: MAIL FROM:<...>
RCPT TO:<...>
...
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Note that the client omitted the QHLO at the start of the previous
connection. This simplification avoids the following situation where
it has to switch back and forth between SMTP and TLS at the start of
the TLS handshake.
...
S: SMTP <qsmtp-greet>
C: QHLO <domain>
QTLS
TLS client hello
S: SMTP 220 OK
TLS server hello, certificate, etc.
...
With pipelined AUTH, the MAIL command is in the client's 5th packet.
C: TCP SYN
S: SYN/ACK
C: ACK
S: SMTP <qsmtp-greet>
C: QTLS
TLS client hello
S: server hello, certificate, etc.
C: key exchange, change cipher, finish handshake
S: change cipher, finish handshake
SMTP <qsmtp-greet>
C: QHLO <domain>
AUTH PLAIN <creds>
MAIL FROM:<...>
RCPT TO:<...>
...
S: 220 OK
235 OK
250 OK
250 OK
...
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The following shows the use of QTLS with a TLS session cache hit and
use of the full QHLO command after TLS is started. This form is
simpler than pipelined STARTTLS (as shown below) but slightly less
efficient. The MAIL coomand is in the client's 4th packet.
C: TCP SYN
S: SYN/ACK
C: ACK
S: SMTP <qsmtp-greet>
C: QTLS
TLS client hello
S: server hello, change cipher, finish handshake
C: change cipher, finish handshake
SMTP QHLO <domain> <qhlo-id>
AUTH PLAIN <creds>
MAIL FROM:<...>
RCPT TO:<...>
...
S: SMTP <qsmtp-greet>
220 OK
235 OK
250 OK
250 OK
...
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The following shows a successful full QUICKSTART connection. The
MAIL command is in the client's 4th packet.
C: TCP SYN
S: SYN/ACK
C: ACK
SMTP QHLO <domain> <qhlo-id>
STARTTLS
TLS client hello
S: SMTP <qsmtp-greet>
220 OK
220 OK
TLS server hello, certificate, etc.
C: key exchange, change cipher, finish handshake
S: change cipher, finish handshake
C: SMTP QHLO <domain> <qhlo-id>
AUTH PLAIN <creds>
MAIL FROM:<...>
RCPT TO:<...>
...
S: 220 OK
235 OK
250 OK
250 OK
...
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If the QUICKSTART handshake fails, the server rejects the initial
pipelined commands and discards the first TLS client hello, and the
client falls back to basic QUICKSTART. The MAIL command is in the
client's 5th packet, the same as basic QUICKSTART without the failed
handshake.
C: TCP SYN
S: SYN/ACK
C: ACK
SMTP QHLO <domain> <qhlo-id>
STARTTLS
TLS client hello
S: SMTP <qsmtp-greet>
520 bad QHLO ID
503 bad sequence of commands
C: QHLO <domain> <qhlo-id>
QTLS
TLS client hello
S: SMTP 220 OK
TLS server hello, certificate, etc.
C: key exchange, change cipher, finish handshake
S: change cipher, finish handshake
<qsmtp-greet>
C: QHLO <domain>
AUTH PLAIN <creds>
MAIL FROM:<...>
RCPT TO:<...>
...
S: 220 OK
235 OK
250 OK
250 OK
...
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The following shows a successful full QUICKSTART connection with a
TLS session cache hit. The MAIL command is in the client's 3rd
packet.
C: TCP SYN
S: SYN/ACK
C: ACK
SMTP QHLO <domain> <qhlo-id>
STARTTLS
TLS client hello
S: SMTP <qsmtp-greet>
220 OK
220 OK
TLS server hello, change cipher, finish handshake
C: change cipher, finish handshake
SMTP QHLO <domain> <qhlo-id>
AUTH PLAIN <creds>
MAIL FROM:<...>
RCPT TO:<...>
...
S: 220 OK
235 OK
250 OK
250 OK
...
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Author's Address
Tony Finch
University of Cambridge Computing Service
New Museums Site
Pembroke Street
Cambridge CB2 3QH
ENGLAND
Phone: +44 797 040 1426
Email: dot at dotat.at
URI: http://dotat.at/
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Full Copyright Statement
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This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
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Finch Expires August 28, 2007 [Page 28]
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