Network Working Group                                          T. Hansen
Request for Comments: 3887                             AT&T Laboratories
Category: Standards Track                                 September 2004


                   Message Tracking Query Protocol

Status of this Memo

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

Copyright Notice

  Copyright (C) The Internet Society (2004).

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 Message Tracking Query Protocol that is used in conjunction with
  extensions to the ESMTP protocol to provide a complete message
  tracking solution for the Internet.

1.  Introduction

  The Message Tracking Models and Requirements document
  [RFC-MTRK-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, [RFC-MTRK-ESMTP] and [RFC-MTRK-TSN],
  describe a complete message tracking solution that satisfies those
  requirements.  The memo [RFC-MTRK-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 [RFC-MTRK-TSN] describes the message/tracking-status
  [RFC-MIME] media type that is used to report tracking status
  information.  Using the model document's terminology, this solution
  uses active enabling and active requests with both request and
  chaining referrals.





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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 BCP 14, RFC 2119
  [RFC-KEYWORDS].

  All syntax descriptions use the ABNF specified by [RFC-ABNF].
  Terminal nodes not defined elsewhere in this document are defined in
  [RFC-ABNF], [RFC-URI], [RFC-MTRK-ESMTP], [RFC-SMTP], or
  [RFC-SMTPEXT].

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 1038.

  When an MTQP client wishes to make use of the message tracking
  service, it establishes a TCP connection with the server host, as
  recorded from the initial message submission or as returned by a
  previous tracking request.  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" and a protocol name of "tcp", as in
  _mtqp._tcp.smtp3.example.com.  (See the "Usage rules" section in
  [RFC-SRV] for details.)  If the SRV records do not exist, the MTQP
  client then does an address record lookup for the server host.  When
  the connection is established, the MTQP server sends a greeting.  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 different
  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 address
  record.  Both mail and MTQP clients will access that host directly.

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






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  A mail system that uses multihomed 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 service.  In both cases, note that the tracking
  service MUST be able to handle the queries for all messages accepted
  by that mail system.

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
  characters.  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
  success 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 followed 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-parsable,
  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
  debugging problems.

  In a multi-line success response, each subsequent line is terminated
  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
  consisting 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



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  period.  When examining 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 indicator.

2.4.  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
  information is available; or it may perform a chaining operation
  itself, gathering 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 administrative decision
  and is not further mandated by this document.

  If a server chooses to perform a chaining operation itself, it MUST
  provide a response within 2 minutes, and SHOULD return a "no further
  information is available" response if it cannot provide an answer at
  the end of that time limit.

2.5.  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, unrecognized commands, or total connection time, or MAY use
  other criteria, to prevent denial of service attacks.

  An MTQP client MAY have an inactivity autologout timer while waiting
  for a response from the server.  Since an MTQP server may be a
  firewall, and may be chaining information from other servers, such a
  timer MUST be at least 2 minutes in duration.







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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 "unavailable".

     "/" "unavailable"
     "/" "admin"

  The reason code "/admin" SHOULD be used when the service is
  unavailable for administrative reasons.  The reason code
  "/unavailable" SHOULD 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.  (See below.)

  One option specification is defined here:

  STARTTLS [1*WSP "required"]

  This capability MUST be listed if the optional STARTTLS command is
  enabled on the MQTP server and one or more certificates have been
  properly installed.

  It has one optional parameter: the word "required" (The parameters
  for STARTTLS are case-insensitive).  If the server requires that TLS
  be used for some of the domains the server handles, the server MUST
  specify the "required" parameter.









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3.1.  Examples

  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: vnd.com.example.option2 with parameters private to example.com
  S: vnd.com.example.option3 with a very long
  S:  list of parameters
  S: .

4.  TRACK Command

  Syntax:

  track-command = "TRACK" 1*WSP unique-envid 1*WSP mtrk-secret CRLF
    mtrk-secret = base64

  Unique-envid is defined in [RFC-MTRK-ESMTP].  Mtrk-secret is the
  secret A described in [RFC-MTRK-ESMTP], encoded using base64.

  When the client issues the TRACK command, and the user is validated,
  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 [RFC-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 [RFC-MIME]
  body part.  The MIME body part MUST be of type multipart/related,
  with subparts of message/tracking-status, as defined in
  [RFC-MTRK-TSN].  The response contains the tracking information about
  the email message that used the given tracking-id.  A negative
  response to the TRACK command may include these reason codes:





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     "/" "tls-required"
     "/" "admin"
     "/" "unavailable"
     "/" "noinfo"
     "/" "insecure"

  The reason code "/tls-required" SHOULD be used when the server has
  decided to require TLS.  The reason code "/admin" SHOULD be used when
  the server has become unavailable, due to administrative reasons,
  since the connection was initialized.  The reason code "/unavailable"
  SHOULD be used when the server has become unavailable, for other
  reasons, since the connection was initialized.  The reason code
  "/insecure" is described later.

  If a message has not been seen by the MTQP server, the server MUST
  choose between two choices: it MAY return a positive response with an
  action field of "opaque" in the tracking information, or it MAY
  return a negative response with a reason code of "noinfo".

4.1.  Examples

  In each of the examples below, the unique-envid is
  "<[email protected]>", 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 <[email protected]> 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: [email protected]
S: Reporting-MTA: dns; example2.com
S: Arrival-Date: Mon, 1 Jan 2001 15:15:15 -0500
S:
S: Original-Recipient: rfc822; [email protected]
S: Final-Recipient: rfc822; [email protected]
S: Action: delivered
S: Status: 2.5.0
S:
S: --%%%%--
S: .





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Example #7      Message Transferred:
C: TRACK <[email protected]> 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: [email protected]
S: Reporting-MTA: dns; example2.com
S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
S:
S: Original-Recipient: rfc822; [email protected]
S: Final-Recipient: rfc822; [email protected]
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:
S: --%%%%--
S: .

Example #8 Message Delayed and a Dot-Stuffed Header:
C: TRACK <[email protected]> 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: [email protected]
S: Reporting-MTA: dns; example2.com
S: Arrival-Date: Mon, 1 Jan 2001 15:15:15 -0500
S:
S: Original-Recipient: rfc822; [email protected]
S: Final-Recipient: rfc822; [email protected]
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: .






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Example #9 Two Users, One Relayed, One Failed:
C: TRACK <[email protected]> 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: [email protected]
S: Reporting-MTA: dns; example2.com
S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
S:
S: Original-Recipient: rfc822; [email protected]
S: Final-Recipient: rfc822; [email protected]
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; [email protected]
S: Final-Recipient: rfc822; [email protected]
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:
C: TRACK <[email protected]> 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: [email protected]
S: Reporting-MTA: dns; example2.com
S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
S:
S: Original-Recipient: rfc822; [email protected]
S: Final-Recipient: rfc822; [email protected]
S: Action: relayed
S: Status: 2.1.9
S: Remote-MTA: dns; smtp.example3.com
S: Last-Attempt-Date: Mon, 1 Jan 2001 19:15:03 -0500
S:



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S: --%%%%
S: Content-Type: message/tracking-status
S:
S: Original-Envelope-Id: [email protected]
S: Reporting-MTA: dns; smtp.example3.com
S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
S:
S: Original-Recipient: rfc822; [email protected]
S: Final-Recipient: rfc822; [email protected]
S: Action: delivered
S: Status: 2.5.0
S:
S: --%%%%--
S: .

Example #11 Firewall, Combining Per-Recipient Blocks:
C: TRACK <[email protected]> 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: [email protected]
S: Reporting-MTA: dns; example2.com
S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
S:
S: Original-Recipient: rfc822; [email protected]
S: Final-Recipient: rfc822; [email protected]
S: Action: relayed
S: Status: 2.1.9
S: Remote-MTA: dns; smtp.example3.com
S: Last-Attempt-Date: Mon, 1 Jan 2001 19:15:03 -0500
S:
S: Original-Recipient: rfc822; [email protected]
S: Final-Recipient: rfc822; [email protected]
S: Action: delivered
S: Status:2.5.0
S:
S: --%%%%--
S: .










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Example #12 Firewall, Hiding System Names Behind the Firewall:
C: TRACK <[email protected]> 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: [email protected]
S: Reporting-MTA: dns; example2.com
S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
S:
S: Original-Recipient: rfc822; [email protected]
S: Final-Recipient: rfc822; [email protected]
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: [email protected]
S: Reporting-MTA: dns; example2.com
S: Arrival-Date: Mon,  1 Jan 2001 15:15:15 -0500
S:
S: Original-Recipient: rfc822; [email protected]
S: Final-Recipient: rfc822; [email protected]
S: Action: delivered
S: Status: 2.5.0
S:
S: --%%%%--
S: .

5.  COMMENT Command

  Syntax:

    comment-command =  "COMMENT" opt-text CRLF
           opt-text = [WSP *(VCHAR / WSP)]

  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.







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6.  STARTTLS Command

  Syntax:

    starttls-command = "STARTTLS" 1*WSP domain *WSP CRLF
              domain = (sub-domain 1*("." sub-domain))

  TLS [TLS] is a popular mechanism for enhancing TCP communications
  with confidentiality and authentication.  All MTQP servers MUST
  implement TLS.  However, TLS MAY be disabled by a server
  administrator, either explicitly or by failing to install any
  certificates for TLS to use.  If an MTQP server supports TLS and has
  one or more certificates available it MUST include "STARTTLS" in the
  option specifications list on protocol startup.

     Note: TLS SHOULD be enabled on MQTP servers whenever possible.

  The parameter MUST be a fully qualified domain name (FQDN).  A client
  MUST specify the hostname it believes it is speaking with so that the
  server may respond with the proper TLS certificate.  This is useful
  for virtual servers that provide message tracking for multiple
  domains (i.e., virtual hosting).

  If the server returns a negative response, it MAY use one of the
  following response codes:
     "/" "unsupported"
     "/" "unavailable"
     "/" "tls-in-progress"
     "/" "bad-fqdn"

  If TLS is not supported, then a response code of "/unsupported"
  SHOULD be used.  If TLS is not available for some other reason, then
  a response code of "/unavailable" SHOULD be used.  If a TLS session
  is already in progress, then it is a protocol error and "-BAD" MUST
  be returned with a response code of "/tls-in-progress".  If there is
  a mismatch between the supplied FQDN and the FQDN found in the
  dNSName field of the subjectAltName extension of the server's
  certificate [RFC-X509], then it is a protocol error and "-BAD" MUST
  be returned with a response code of "/bad-fqdn".

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

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






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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
  authentication and confidentiality achieved.  The MTQP client and
  server may decide to move ahead even if the TLS negotiation ended
  with no authentication and/or no confidentiality because most MTQP
  services are performed with no authentication and no confidentiality,
  but some MTQP clients or servers may want to continue only if a
  particular level of authentication and/or confidentiality was
  achieved.

  If the MTQP client decides that the level of authentication or
  confidentiality 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
  confidentiality is not high enough for it to continue, it MAY abort
  the connection.  If it decides that the level of authentication or
  confidentiality is not high enough for it to continue, and it does
  not abort the connection, it SHOULD reply to every MTQP command 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 connection
  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 been 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
  session is already active.




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7.  QUIT Command

     Syntax:

       quit-command = "QUIT" CRLF

  When the client issues the QUIT command, the MTQP session terminates.
  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 (if the client is on an
  operating system where this does not cause problems).

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.

8.1.  Examples

  The following two examples are identical:

  Example #13 :
  C: TRACK <tracking-id> YWJjZGVmZ2gK
  S: +OK+ Tracking information follows
  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: .














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  Example #14 :
  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.  The MTQP URI Scheme

9.1.  Intended usage

  The MTQP URI scheme is used to designate MTQP servers on Internet
  hosts accessible using the MTQP protocol.  It performs an MTQP query
  and returns tracking status information.

9.2.  URI Scheme Name

  The name of the URI scheme is "mtqp".

9.3.  URI Scheme Syntax

  An MTQP URI takes one of the following forms:

     mtqp://<mserver>/track/<unique-envid>/<mtrk-secret>
     mtqp://<mserver>:<port>/track/<unique-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 (unique-envid) and authorization secret (mtrk-
  secret).  The path element "/track/" MUST BE treated case
  insensitively, but the unique-envid and mtrk-secret MUST NOT be.

9.3.1.  Formal Syntax

  This is an ABNF description of the MTQP URI.

  mtqp-uri = "mtqp://" authority "/track/" unique-envid "/" mtrk-secret








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9.4.  Encoding Rules

  The encoding of unique-envid is discussed in [RFC-MTRK-ESMTP].
  Mtrk-secret is required to be base64 encoded.  If the "/", "?" and
  "%" octets appear in unique-envid or mtrk-secret, they are further
  required to be represented by a "%" followed by two hexadecimal
  characters.  (The two characters give the hexadecimal representation
  of that octet).

10.  IANA Considerations

  System port number 1038 has been assigned to the Message Tracking
  Query Protocol by the Internet Assigned Numbers Authority (IANA).

  The service name "MTQP" has been registered with the IANA.

  The IANA has also registered the URI registration template found in
  Appendix A in accordance with [BCP35].

  This document requests that IANA maintain one new registry: MTQP
  options.  The registry's purpose is to register options to this
  protocol.  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

  One MTQP option is defined in this document, with the following
  registration definition:

     option identifier: STARTTLS
     option parameters: none
     added commands: STARTTLS
     standard commands affected: none
     specification reference: RFC 3887
     discussion: see RFC 3887

  Additional vendor-specific options for this protocol have names that
  begin with "vnd.".  After the "vnd." would appear the reversed domain
  name of the vendor, another dot ".", and a name for the option
  itself.  For example, "vnd.com.example.extinfo" might represent a




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  vendor-specific extension providing extended information by the owner
  of the "example.com" domain.  These names MAY be registered with
  IANA.

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 maximum 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 exposure 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
  confidentiality, they are not securing tracking queries with any
  prior or successive MTQP servers.

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

  The MTQP client and server should note carefully the result of the
  TLS negotiation.  If the negotiation results in no confidentiality,
  or if it results in confidentiality 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 commands.

  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.





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  Similarly, the identity of the server as expressed in the server's
  certificate should be cached, and an alarm generated if they do not
  match in 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 (or better) 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.

mtqp-uri = "mtqp://" authority "/track/" unique-envid "/" mtrk-secret

conversation = command-response *(client-command command-response)

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

track-command = "TRACK" 1*WSP unique-envid 1*WSP mtrk-secret CRLF
mtrk-secret = base64

starttls-command = "STARTTLS" 1*WSP domain *WSP CRLF
domain = (sub-domain 1*("." sub-domain))

quit-command = "QUIT" CRLF

comment-command = "COMMENT" opt-text CRLF







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; 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

NAMECHAR = ALPHA / DIGIT / "-" / "_"

response-info = *(      "/" ( "admin" / "unavailable" / "unsupported"
/ "tls-in-progress" / "insecure" / "tls-required" / 1*NAMECHAR ) )

13.  Acknowledgements

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




















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14.  References

14.1.  Normative References

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

  [RFC-ABNF]         Crocker, D., Ed. and P. Overell, "Augmented BNF
                     for Syntax Specifications: ABNF", RFC 2234,
                     November 1997.

  [RFC-SRV]          Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS
                     RR for specifying the location of services (DNS
                     SRV)", RFC 2782, February 2000.

  [RFC-SMTP]         Klensin, J., "Simple Mail Transfer Protocol", RFC
                     2821, April 2001.

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

  [RFC-MTRK-ESMTP]   Allman, E. and T. Hansen, "SMTP Service Extension
                     for Message Tracking", RFC 3885, September 2004.

  [RFC-MTRK-MODEL]   Hansen, T., "Message Tracking Models and
                     Requirements", RFC 3885, September 2004.

  [RFC-MTRK-TSN]     Allman, E., "The Message/Tracking-Status MIME
                     Extension", RFC 3886, September 2004.

  [RFC-URI]          Berners-Lee, T., Fielding, R. and L. Masinter,
                     "Uniform Resource Identifiers (URI): Generic
                     Syntax", RFC 2396, August 1998.

  [TLS]              Dierks, T. and C. Allen, "The TLS Protocol Version
                     1.0", RFC 2246, January 1999.













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14.2.  Informational References

  [BCP35]            Petke, R. and I. King, "Registration Procedures
                     for URL Scheme Names", BCP 35, RFC 2717, November
                     1999.

  [RFC-SHA1]         Eastlake, D. and P. Jones, "US Secure Hash
                     Algorithm 1 (SHA1)", RFC 3174, September 2001.

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

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

  [RFC-X509]         Housley, R., Polk, W., Ford, W. and D. Solo,
                     "Internet X.509 Public Key Infrastructure
                     Certificate and Certificate Revocation List (CRL)
                     Profile", RFC 3280, April 2002.

  [POP3]             Myers, J. and M. Rose, "Post Office Protocol -
                     Version 3", STD 53, RFC 1939, May 1996.

  [NNTP]             Kantor, B. and P. Lapsley, "Network News Transfer
                     Protocol", RFC 977, February 1986.
























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Appendix A. MTQP URI Registration Template

  Scheme name: mtqp

  Scheme syntax: see section 9.1

  Character encoding considerations: see section 9.4

  Intended usage: see section 9.3

  Applications and/or protocols which use this scheme: MTQP

  Interoperability considerations: as specified for MTQP

  Security considerations: see section 11.0

  Relevant publications: [RFC-MTRK-ESMTP], [RFC-MTRK-MODEL],
  [RFC-MTRK-TSN]

  Contact: MSGTRK Working Group

  Author/Change Controller: IESG

Author's Address

  Tony Hansen
  AT&T Laboratories
  Middletown, NJ 07748
  USA

  Phone: +1.732.420.8934
  EMail: [email protected]



















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Full Copyright Statement

  Copyright (C) The Internet Society (2004).

  This document is subject to the rights, licenses and restrictions
  contained in BCP 78, and except as set forth therein, the authors
  retain all their rights.

  This document and the information contained herein are provided on an
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Acknowledgement

  Funding for the RFC Editor function is currently provided by the
  Internet Society.







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