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Internet Draft                                                 T. Hansen
draft-ietf-msgtrk-mtqp-03.txt                          AT&T Laboratories
Valid for six months                                        July 1, 2001



                    Message Tracking Query Protocol

                    <draft-ietf-msgtrk-mtqp-03.txt>

                         Authors' version: 1.7

     Status of this Memo

     This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

     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.

     This memo and its companions are discussed on the MSGTRK working
group mailing list, ietf-msgtrk@imc.org.  To subscribe, send a message
with the word "subscribe" in the body (on a line by itself) to the
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be found at http://www.ietf.org/archive/msgtrk.

Copyright Notice

     Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract

     Customers buying enterprise message systems often ask: Can I track
the messages?  Message tracking is the ability to find out the path that
a particular message has taken through a messaging system and the
current routing status of that message.  This document describes the



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Message Tracking Query Protocol that is used in conjunction with exten-
sions to the ESMTP protocol to provide a complete message tracking solu-
tion for the Internet.

1.  Introduction

     The Message Tracking Models and Requirements document [DRAFT-
TRACK-MODEL] discusses the models that message tracking solutions could
follow, along with requirements for a message tracking solution that can
be used with the Internet-wide message infrastructure.  This memo and
its companions, [DRAFT-TRACK-ESMTP] and [DRAFT-TRACK-TSN], describe a
complete message tracking solution that satisfies those requirements.
The memo [DRAFT-TRACK-ESMTP] defines an extension to the SMTP service
that provides the information necessary to track messages.  This memo
defines a protocol that can be used to query the status of messages that
have been transmitted on the Internet via SMTP.  The memo [DRAFT-TRACK-
TSN] describes the message/tracking-status MIME media type that is used
to report tracking status information.  Using the model document's ter-
minology, this solution uses active enabling and active requests with
both request and chaining referrals.

1.1.  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 [RFC-KEYWORDS].

     All syntax descriptions use the ABNF specified by [RFC-ABNF].  Ter-
minal nodes not defined elsewhere in this document are defined in [RFC-
ABNF], [RFC-URI], [DRAFT-TRACK-ESMTP] or [RFC-SMTPEXT].

1.2.  Changes Made for -02

     This section will be removed before publication.

     Provided information on lookup for an MTQP server: SRV MTQP, then
MX, then A.

     Provided a section on firewall considerations

     Provided a section on service DNS considerations

     At IANA's request, left the port number as XXXX and added more
information on the option registry.

     Added text on various error conditions and fixed ABNF for error
response codes.




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     Fleshed out the tracking examples.

2.  Basic Operation

     The Message Tracking Query Protocol (MTQP) is similar to many other
line-oriented Internet protocols, such as [POP3] and [NNTP].  Initially,
the server host starts the MTQP service by listening on TCP port XXXX
(TBD by IANA).

     When an MTQP client wishes to make use of the message tracking ser-
vice, it establishes a TCP connection with the server host.  To find the
server host, the MTQP client first does an SRV lookup for the server
host using DNS SRV records, with a service name of "mtqp".  (See the
"Usage rules" section in [RFC-SRV] for details.)  If the host is not
found, the MTQP client then does an MX lookup for the server host using
DNS MX records, as specified in [RFC-DNS] and revised by [RFC-HOSTS].
If the host is still not found, the MTQP client then does an A record
lookup for the server host.

     When the connection is established, the MTQP server sends a greet-
ing.  The MTQP client and MTQP server then exchange commands and
responses (respectively) until the connection is closed or aborted.

2.1.  Tracking Service DNS Considerations

     Because of the ways server host lookups are performed, many dif-
ferent tracking server host configurations are supported.

     A mail system that uses a single mail server host and has the MTQP
server host on the same server host will most likely have a single MX
record pointing at the server host, and if not, will have an A record.
Both mail and MTQP clients will access that host directly.

     A mail system that uses a single mail server host, but wants track-
ing queries to be performed on a different machine, MUST have an SRV
MTQP record pointing at that different machine.

     A mail system that uses multiple mail servers has two choices for
providing tracking services: either all mail servers must be running
tracking servers that are able to retrieve information on all messages,
or the tracking service must be performed on one (or more) machine(s)
that are able to retrieve information on all messages.  In the former
case, no additional DNS records are needed beyond the MX records already
in place for the mail system.  In the latter case, SRV MTQP records are
needed that point at the machine(s) that are running the tracking ser-
vice.  In both cases, note that the tracking service for a given mail
domain MUST be able to handle the queries for all messages destined for
that mail domain.



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2.2.  Commands

     Commands in MTQP consist of a case-insensitive keyword, possibly
followed by one or more parameters.  All commands are terminated by a
CRLF pair.  Keywords and parameters consist of printable ASCII charac-
ters.  Keywords and parameters are separated by whitespace (one or more
space or tab characters).  A command line is limited to 998 characters
before the CRLF.

2.3.  Responses

     Responses in MTQP consist of a status indicator that indicates suc-
cess or failure.  Successful commands may also be followed by additional
lines of data.  All response lines are terminated by a CRLF pair and are
limited to 998 characters before the CRLF.  There are several status
indicators:  "+OK" indicates success; "+OK+" indicates a success fol-
lowed by additional lines of data, a multi-line success response; "-
TEMP" indicates a temporary failure; "-ERR" indicates a permanent
failure; and "-BAD" indicates a protocol error (such as for unrecognized
commands).

     A status indicator MAY be followed by a series of machine-
parseable, case-insensitive response information giving more data about
the errors.  These are separated from the status indicator and each
other by a single slash character ("/", decimal code 47).  Following
that, there MAY be white space and a human-readable text message.  The
human-readable text message is not intended to be presented to the end
user, but should be appropriate for putting in a log for use in debug-
ging problems.

     In a multi-line success response, each subsequent line is ter-
minated by a CRLF pair and limited to 998 characters before the CRLF.
When all lines of the response have been sent, a final line is sent con-
sisting of a single period (".", decimal code 046) and a CRLF pair.  If
any line of the multi-line response begins with a period, the line is
"dot-stuffed" by prepending the period with a second period.  When exa-
mining a multi-line response, the client checks to see if the line
begins with a period.  If so, and octets other than CRLF follow, the
first octet of the line (the period) is stripped away.  If so, and if
CRLF immediately follows the period, then the response from the MTQP
server is ended and the line containing the ".CRLF" is not considered
part of the multi-line response.

     An MTQP server MUST respond to an unrecognized, unimplemented, or
syntactically invalid command by responding with a negative -BAD status
indicator.  A server MUST respond to a command issued when the session
is in an incorrect state by responding with a negative -ERR status indi-
cator.



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2.4.  Optional Timers

     An MTQP server MAY have an inactivity autologout timer.  Such a
timer MUST be of at least 10 minutes in duration.  The receipt of any
command from the client during that interval should suffice to reset the
autologout timer.  An MTQP server MAY limit the number of commands or
total connection time to prevent denial of service attacks.

2.5.  Firewall Considerations

     A firewall mail gateway has two choices when receiving a tracking
query for a host within its domain: it may return a response to the
query that says the message has been passed on, but no further informa-
tion is available; or it may perform a chaining operation itself, gath-
ering information on the message from the mail hosts behind the
firewall, and returning to the MTQP client the information for each
behind-the-firewall hop, or possibly just the final hop information,
possibly also disguising the names of any hosts behind the firewall.
Which option is picked is an adminstrative decision and is not further
mandated by this document.

3.  Initialization and Option Response

     Once the TCP connection has been opened by an MTQP client, the MTQP
server issues an initial status response that indicates its readiness.
If the status response is positive (+OK or +OK+), the client may proceed
with other commands.

     The initial status response MUST include the response information
"/MTQP".  Negative responses MUST include a reason code as response
information.  The following reason codes are defined here; unrecognized
reason codes added in the future may be treated as equivalent to "una-
vailable".
     "/" "unavailable"
     "/" "admin"

     The reason code "/admin" may be used when the service is unavail-
able for administrative reasons.  The reason code "/unavailable" may be
used when the service is unavailable for other reasons.

     If the server has any options enabled, they are listed as the
multi-line response of the initial status response, one per line.  An
option specification consists of an identifier, optionally followed by
option-specific parameters.  An option specification may be continued
onto additional lines by starting the continuation lines with white
space.  The option identifier is case insensitive.  Option identifiers
beginning with the characters "vnd." are reserved for vendor use.




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     One option specification is defined here:

     STARTTLS

This capability MUST be listed if the optional STARTTLS command is sup-
ported by the MTQP server.  It has no parameters.

     Example #1 (no options):
     S: +OK/MTQP MTQP server ready

     Example #2 (service temporarily unavailable):
     S: -TEMP/MTQP/admin Service down for admin, call back later

     Example #3 (service permanently unavailable):
     S: -ERR/MTQP/unavailable Service down

     Example #4 (alternative for no options):
     S: +OK+/MTQP MTQP server ready
     S: .

     Example #5 (options available):
     S: +OK+/MTQP MTQP server ready
     S: starttls
     S: Option2 with parameters
     S: Option3 with a very long
     S:  list of parameters
     S: .

4.  TRACK Command

     Syntax:
          "TRACK" 1*WSP envid 1*WSP mtrk-secret CRLF

          mtrk-secret = base64

     Envid is defined in [DRAFT-TRACK-ESMTP].  Mtrk-secret is the secret
A described in [DRAFT-TRACK-ESMTP], encoded using base64.

     When the client issues the TRACK command, and the user is vali-
dated, the MTQP server retrieves tracking information about an email
message.  To validate the user, the value of mtrk-secret is hashed using
SHA1, as described in [NIST-SHA1].  The hash value is then compared with
the value passed with the message when it was originally sent.  If the
hash values match, the user is validated.

     A successful response MUST be multi-line, consisting of a [MIME]
body part.  The MIME body part must be of type multipart/related, with
subparts of message/tracking-status, as defined in [DRAFT-TRACK-TSN].



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The response contains the tracking information about the email message
that used the given tracking-id.


     In each of the examples below, the envid is "<12345-
20010101@example.com>", the secret A is "abcdefgh", and the SHA1 hash B
is (in hex) "734ba8b31975d0dbae4d6e249f4e8da270796c94".  The message
came from example.com and the MTQP server is example2.com.

     Example #6 Message Delivered:
     C: TRACK <12345-20010101@example.com> YWJjZGVmZ2gK
     S: +OK+ Tracking information follows
     S: Content-Type: multipart/related; boundary=%%%%; type=tracking-status
     S:
     S: --%%%%
     S: Content-Type: message/tracking-status
     S:
     S: Original-Envelope-Id: 12345-20010101@example.com
     S: Reporting-MTA: dns; example2.com
     S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
     S:
     S: Original-Recipient: rfc822; user1@example1.com
     S: Final-Recipient: rfc822; user1@example1.com
     S: Action: delivered
     S: Status: 2.5.0
     S:
     S: --%%%%--
     S: .

     Example #7 Message Transferred:
     C: TRACK <12345-20010101@example.com> YWJjZGVmZ2gK
     S: +OK+ Tracking information follows
     S: Content-Type: multipart/related; boundary=%%%%; type=tracking-status
     S:
     S: --%%%%
     S: Content-Type: message/tracking-status
     S:
     S: Original-Envelope-Id: 12345-20010101@example.com
     S: Reporting-MTA: dns; example2.com
     S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
     S:
     S: Original-Recipient: rfc822; user1@example1.com
     S: Final-Recipient: rfc822; user1@example1.com
     S: Action: transferred
     S: Remote-MTA: dns; example3.com
     S: Last-Attempt-Date: Mon,  1 Jan 2001 19:15:03 -0500
     S: Status: 2.4.0
     S:



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     S: --%%%%--
     S: .

     Example #8 Message Delayed and a DotStuffed Header:
     C: TRACK <12345-20010101@example.com> YWJjZGVmZ2gK
     S: +OK+ Tracking information follows
     S: Content-Type: multipart/related; boundary=%%%%; type=tracking-status
     S: ..Dot-Stuffed-Header: as an example
     S:
     S: --%%%%
     S: Content-Type: message/tracking-status
     S:
     S: Original-Envelope-Id: 12345-20010101@example.com
     S: Reporting-MTA: dns; example2.com
     S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
     S:
     S: Original-Recipient: rfc822; user1@example1.com
     S: Final-Recipient: rfc822; user1@example1.com
     S: Action: delayed
     S: Status: 4.4.1 (No answer from host)
     S: Remote-MTA: dns; example3.com
     S: Last-Attempt-Date: Mon,  1 Jan 2001 19:15:03 -0500
     S: Will-Retry-Until: Thu,  4 Jan 2001 15:15:15 -0500
     S:
     S: --%%%%--
     S: .

     Example #9 Two Users, One Relayed, One Failed:
     C: TRACK <12345-20010101@example.com> YWJjZGVmZ2gK
     S: +OK+ Tracking information follows
     S: Content-Type: multipart/related; boundary=%%%%; type=tracking-status
     S:
     S: --%%%%
     S: Content-Type: message/tracking-status
     S:
     S: Original-Envelope-Id: 12345-20010101@example.com
     S: Reporting-MTA: dns; example2.com
     S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
     S:
     S: Original-Recipient: rfc822; user1@example1.com
     S: Final-Recipient: rfc822; user1@example1.com
     S: Action: relayed
     S: Status: 2.1.9
     S: Remote-MTA: dns; example3.com
     S: Last-Attempt-Date: Mon,  1 Jan 2001 19:15:03 -0500
     S:
     S: Original-Recipient: rfc822; user2@example1.com
     S: Final-Recipient: rfc822; user2@example1.com



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     S: Action: failed
     S: Status 5.2.2 (Mailbox full)
     S: Remote-MTA: dns; example3.com
     S: Last-Attempt-Date: Mon,  1 Jan 2001 19:15:03 -0500
     S:
     S: --%%%%--
     S: .

     Example #10 Firewall, Hiding System Names Behind the Firewall:
     C: TRACK <12345-20010101@example.com> YWJjZGVmZ2gK
     S: +OK+ Tracking information follows
     S: Content-Type: multipart/related; boundary=%%%%; type=tracking-status
     S:
     S: --%%%%
     S: Content-Type: message/tracking-status
     S:
     S: Original-Envelope-Id: 12345-20010101@example.com
     S: Reporting-MTA: dns; example2.com
     S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
     S:
     S: Original-Recipient: rfc822; user1@example1.com
     S: Final-Recipient: rfc822; user1@example1.com
     S: Action: relayed
     S: Status: 2.1.9
     S: Remote-MTA: dns; example2.com
     S: Last-Attempt-Date: Mon,  1 Jan 2001 19:15:03 -0500
     S:
     S: --%%%%
     S: Content-Type: message/tracking-status
     S:
     S: Original-Envelope-Id: 12345-20010101@example.com
     S: Reporting-MTA: dns; example2.com
     S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
     S:
     S: Original-Recipient: rfc822; user1@example1.com
     S: Final-Recipient: rfc822; user1@example1.com
     S: Action: delivered
     S: Status: 2.5.0
     S:
     S: --%%%%--
     S: .

5.  COMMENT Command

     Syntax:
          "COMMENT" opt-text CRLF

          opt-text = [WSP *(VCHAR / WSP)]



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     When the client issues the COMMENT command, the MTQP server MUST
respond with a successful response (+OK or +OK+).  All optional text
provided with the COMMENT command are ignored.

6.  STARTTLS Command

     Syntax:
          "STARTTLS" CRLF

     TLS [TLS], more commonly known as SSL, is a popular mechanism for
enhancing TCP communications with privacy and authentication.  An MTQP
server MAY support TLS.  If an MTQP server supports TLS, it MUST include
"STARTTLS" in the option specifications list on protocol startup.

     If the server returns a negative response, it MAY use one of the
following response codes:
     "/" "unsupported"
     "/" "unavailable"

     If a TLS session is already in progress, then it is a protocol
error and "-BAD" MUST be returned with a response code of "/tlsinpro-
gress".

     After receiving a positive response to a STARTTLS command, the
client MUST start the TLS negotiation before giving any other MTQP com-
mands.

     If the MTQP client is using pipelining, the STARTTLS command must
be the last command in a group.

6.1.  Processing After the STARTTLS Command

     If the TLS handshake fails, the server SHOULD abort the connection.

     After the TLS handshake has been completed, both parties MUST
immediately decide whether or not to continue based on the authentica-
tion and privacy achieved. The MTQP client and server may decide to move
ahead even if the TLS negotiation ended with no authentication and/or no
privacy because most MTQP services are performed with no authentication
and no privacy, but some MTQP clients or servers may want to continue
only if a particular level of authentication and/or privacy was
achieved.

     If the MTQP client decides that the level of authentication or
privacy is not high enough for it to continue, it SHOULD issue an MTQP
QUIT command immediately after the TLS negotiation is complete.  If the
MTQP server decides that the level of authentication or privacy is not
high enough for it to continue, it SHOULD reply to every MTQP command



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from the client (other than a QUIT command) with a negative "-ERR"
response and a response code of "/insecure".

6.2.  Result of the STARTTLS Command

     Upon completion of the TLS handshake, the MTQP protocol is reset to
the initial state (the state in MTQP after a server starts up).  The
server MUST discard any knowledge obtained from the client prior to the
TLS negotiation itself. The client MUST discard any knowledge obtained
from the server, such as the list of MTQP options, which was not
obtained from the TLS negotiation itself.

     At the end of the TLS handshake, the server acts as if the connec-
tion had been initiated and responds with an initial status response
and, optionally, a list of server options.  The list of MTQP server
options received after the TLS handshake MUST be different than the list
returned before the TLS handshake.  In particular, a server MUST NOT
return the STARTTLS option in the list of server options after a TLS
handshake has completed.

     Both the client and the server MUST know if there is a TLS session
active.  A client MUST NOT attempt to start a TLS session if a TLS ses-
sion is already active.

7.  QUIT Command

     Syntax:
          "QUIT" CRLF

     When the client issues the QUIT command, the MTQP session ter-
minates.  The QUIT command has no parameters.  The server MUST respond
with a successful response.  The client may close the session from its
end immediately after issuing this command.

8.  Pipelining

     The MTQP client may elect to transmit groups of MTQP commands in
batches without waiting for a response to each individual command.  The
MTQP server MUST process the commands in the order received.

     Specific commands may place further constraints on pipelining.  For
example, STARTTLS must be the last command in a batch of MTQP commands.

     The following two examples are identical:

     Example #11 :
     C: TRACK <tracking-id> YWJjZGVmZ2gK
     S: +OK+ Tracking information follows



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     S:
     S: ... tracking details #1 go here ...
     S: .
     C: TRACK <tracking-id-2> QUJDREVGR0gK
     S: +OK+ Tracking information follows
     S:
     S: ... tracking details #2 go here ...
     S: .

     Example #12 :
     C: TRACK <tracking-id> YWJjZGVmZ2gK
     C: TRACK <tracking-id-2> QUJDREVGR0gK
     S: +OK+ Tracking information follows
     S:
     S: ... tracking details #1 go here ...
     S: .
     S: +OK+ Tracking information follows
     S:
     S: ... tracking details #2 go here ...
     S: .

9.  URL Format

     The MTQP URL scheme is used to designate MTQP servers on Internet
hosts accessible using the MTQP protocol.  An MTQP URL takes one of the
following forms:

     mtqp://<mserver>/track/<envid>/<mtrk-secret>
     mtqp://<mserver>:<port>/track/<envid>/<mtrk-secret>

     The first form is used to refer to an MTQP server on the standard
port, while the second form specifies a non-standard port.  Both of
these forms specify that the TRACK command is to be issued using the
given tracking id and authorization cookie.  The path element "/track/"
is case insensitive, but the envid and mtrk-secret may not be.

9.1.  MTQP URL Syntax

     This is an ABNF description of the MTQP URL.

     mtqp-url = "mtqp://" net_loc "/track/" envid ":" mtrk-secret

10.  IANA Considerations

     System port number XXXX - TBA by IANA

     The service name to be registered with the Internet Assigned Number
Authority (IANA) is "MTQP".



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     This document requests that IANA maintain one new registry: MTQP
options.  The registry's purpose is to register options to this proto-
col.  Options whose names do not begin with "vnd." MUST be defined in a
standards track or IESG approved experimental RFC.  New MTQP options
MUST include the following information as part of their definition:

     option identifier
     option parameters
     added commands
     standard commands affected
     specification reference
     discussion

     Additional vendor-specific options for this protocol whose names
begin with "vnd."  MUST be registered with IANA on a Firt Come First
Served basis.  It is expected that after the "vnd." would appear an
abbreviated form of the vendor's name that is registering the option,
followed by a second dot "." and a name for the option itself.  For
example, "vnd.example.extinfo" might represent a vendor-specific exten-
sion providing extended information being registered by the "Example,
Inc." company.

11.  Security Considerations

     If the originator of a message were to delegate his or her tracking
request to a third party, this would be vulnerable to snooping over
unencrypted sessions.  The user can decide on a message-by-message basis
if this risk is acceptable.

     The security of tracking information is dependent on the randomness
of the secret chosen for each message and the level of exposure of that
secret.  If different secrets are used for each message, then the max-
imum exposure from tracking any message will be that single message for
the time that the tracking information is kept on any MTQP server.  If
this level of exposure is too much, TLS may be used to reduce the expo-
sure further.

     It should be noted that message tracking is not an end-to-end
mechanism.  Thus, if an MTQP client/server pair decide to use TLS
privacy, they are not securing tracking queries with any prior or suc-
cessive MTQP servers.

     Both the STMP client and server must check the result of the TLS
negotiation to see whether acceptable authentication or privacy was
achieved.  Ignoring this step completely invalidates using TLS for secu-
rity.  The decision about whether acceptable authentication or privacy
was achieved is made locally, is implementation-dependant, and is beyond
the scope of this document.



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     The SMTP client and server should note carefully the result of the
TLS negotiation.  If the negotiation results in no privacy, or if it
results in privacy using algorithms or key lengths that are deemed not
strong enough, or if the authentication is not good enough for either
party, the client may choose to end the MTQP session with an immediate
QUIT command, or the server may choose to not accept any more MTQP com-
mands.

     A man-in-the-middle attack can be launched by deleting the
"STARTTLS" option response from the server.  This would cause the client
not to try to start a TLS session.  An MTQP client can protect against
this attack by recording the fact that a particular MTQP server offers
TLS during one session and generating an alarm if it does not appear in
an option response for a later session.

     If TLS is not used, a tracking request is vulnerable to replay
attacks, such that a snoop can later replay the same handshake again to
potentially gain more information about a message's status.

     Before the TLS handshake has begun, any protocol interactions are
performed in the clear and may be modified by an active attacker.  For
this reason, clients and servers MUST discard any knowledge obtained
prior to the start of the TLS handshake upon completion of the TLS
handshake.

     If a client/server pair successfully performs a TLS handshake and
the server does chaining referrals, then the server SHOULD attempt to
negotiate TLS at the same security level at the next hop.  In a hop-by-
hop scenario, STARTTLS is a request for "best effort" security and
should be treated as such.

     SASL is not used because authentication is per message rather than
per user.

12.  Protocol Syntax

     This is a collected ABNF description of the MTQP protocol.
     conversation = command-response *( client-command command-response )

     # client side
     client-command = track-command / starttls-command / quit-command / comment-command

     track-command = "TRACK" 1*WS envid 1*WS mtrk-secret CRLF

     mtrk-secret = base64

     starttls-command = "STARTTLS" CRLF




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     quit-command = "QUIT" CRLF

     comment-command = "COMMENT" opt-text CRLF

     # server side
     command-response = success-response / temp-response / error-response / bad-response

     temp-response = "-TEMP" response-info opt-text CRLF

     opt-text = [WSP *(VCHAR / WSP)]

     error-response = "-ERR" response-info opt-text CRLF

     bad-response = "-BAD" response-info opt-text CRLF

     success-response = single-line-success / multi-line-success

     single-line-success = "+OK" response-info opt-text CRLF

     multi-line-success = "+OK+" response-info opt-text CRLF *dataline dotcrlf

     dataline = *998OCTET CRLF

     dotcrlf = "." CRLF

     option-list = *option-line

     option-line = identifier opt-text *[CRLF WSP opt-text] CRLF

     identifier = (ALPHA / "_") *(ALPHA / DIGIT / "-" / "_")

     response-info = *( "/" 1*(ALPHA / DIGIT / "-" / "_")


13.  Acknowledgements

     The description of STARTTLS is based on [RFC-SMTP-TLS].

14.  References

     [NIST-SHA1] NIST FIPS  PUB  180-1, "Secure  Hash  Standard",
National Institute of Standards and Technology, U.S. Department of Com-
merce, May 1994.

     [MIME] RFC 2045, N. Freed & N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part One: Format of Internet Message Bodies",
Innosoft, First Virtual, November 1996.




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     [RFC-821] STD 10, RFC 821, J. Postel, "Simple Mail Transfer Proto-
col", University of Southern California / Information Sciences Insti-
tute, August 1982.

     [RFC-822] STD 11, RFC 822, D. Crocker, "Standard for the Format of
ARPA Internet Text Messages", University of Delaware, August 1982.

     [RFC-ABNF] RFC 2234, D. Crocker, Editor, and P. Overell, "Augmented
BNF for Syntax Specifications: ABNF", Internet Mail Consortium, Demon
Internet Ltd., November 1997.

     [RFC-DNS] RFC 974, "Mail routing and the domain system", C. Par-
tridge, January 1986.

     [RFC-ESMTP] RFC 1651, J. Klensin, N. Freed, M. Rose, E. Stefferud,
and D. Crocker, "SMTP Service Extensions", MCI, Innosoft, Dover Beach
Consulting, Inc., network Management Associates, Inc., Silicon Graphics,
Inc., July 1994.

     [RFC-HOSTS] "Requirements for Internet Hosts - Application and Sup-
port", R. Braden, Ed., October 1989.

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

     [RFC-MD5] RFC 1321, R. Rivest, "The MD5 Message-Digest Algorithm",
MIT Laboratory for Computer Science and RSA Data Security, Inc., April
1992.

     [RFC-SMTPEXT] RFC 2554, J. Myers, "SMTP Service Extension for
Authentication", Netscape Communications, March 1999.

     [RFC-SMTP-TLS] RFC2487, P. Hoffman, "SMTP Service Extension for
Secure SMTP over TLS", Internet Mail Consortium, January 1999.

     [RFC-SRV] RFC 2782, A. Gulbrandsen, P. Vixie, L. Esibov, "A DNS RR
for specifying the location of services (DNS SRV)" Troll Technologies,
Internet Software Consortium, Microsoft Corp., February 2000

     [DRAFT-TRACK-ESMTP] draft-ietf-msgtrk-smtpext-*.txt, E. Allman, T.
Hansen, "SMTP Service Extension for Message Tracking", Sendmail, Inc.,
AT&T Laboratories, TBD 2000.

     [DRAFT-TRACK-MODEL] draft-ietf-msgtrk-model-03.txt, T. Hansen,
"Message Tracking Models and Requirements", AT&T Laboratories, November
2000.

     [DRAFT-TRACK-TSN] draft-ietf-msgtrk-trkstat-*.txt, E. Allman, "The



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Message/Tracking-Status MIME Extension", Sendmail, Inc., TBD 2000.

     [RFC-URI] RFC 2396, T. Berners-Lee, R. Fielding, L. Masinter, "Uni-
form Resource Identifiers (URI): Generic Syntax", MIT/LCS, U. C. Irvine,
Xerox Corporation, August 1998.

15.  Author's Address

     Tony Hansen
     AT&T Laboratories
     Lincroft, NJ 07738
     USA

     Phone: +1.732.576.3207
     E-Mail: tony@att.com

16.  Full Copyright Statement

     Copyright (C) The Internet Society (1999).  All Rights Reserved.

     This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it or
assist in its implmentation may be prepared, copied, published and dis-
tributed, in whole or in part, without restriction of any kind, provided
that the above copyright notice and this paragraph are included on all
such copies and derivative works.  However, this document itself may not
be modified in any way, such as by removing the copyright notice or
references to the Internet Society or other Internet organisations,
except as needed for the purpose of developing Internet standards in
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dards process must be followed, or as required to translate it into
languages other than English.

     The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

     This document and the information contained herein is provided on
an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL
NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR
FITNESS FOR A PARTICULAR PURPOSE.

     This document expires January 1, 2002.







Hansen                                                         [Page 17]


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