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Network Working Group                                          J. Levine
Internet-Draft                                      Taughannock Networks
Updates: 5321 (if approved)                                July 30, 2019
Intended status: Standards Track
Expires: January 31, 2020


    Update to Additional Registered Clauses in SMTP Received Headers
             draft-levine-additional-registered-clauses-03

Abstract

   SMTP servers add Received: trace headers to mail messages to track
   their progress This document updates the registration criteria for
   Additional Registered Clauses in those headers to Expert Review, and
   adds new clauses for Server Name Indication (SNI) and sending port
   number (PORT).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on January 31, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  The Server Name Indication clause . . . . . . . . . . . . . .   2
   3.  The Port Number clause  . . . . . . . . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Guidance for Designated Expert  . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Uninformative References  . . . . . . . . . . . . . . . .   4
   Appendix A.  Change history . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   SMTP servers add Received: trace headers to mail messages to track
   their progress.  The syntax of those headers is defined in [RFC5321].
   Each header can include optional Additional Registered Clauses that
   log information related to optional SMTP features.

   This document updates the registration criteria for Additional
   Registered Clauses in those headers to Expert Review, and adds a new
   clause for Server Name Indication (SNI).  The headers can include
   Additional Registered Clauses that add information about optional
   SMTP features.

2.  The Server Name Indication clause

   Server Name Indication or SNI [RFC6066] is an optional TLS feature
   that a TLS client can use to advise a server the name it expects the
   server to have.  When used in the initial negotiation for a STARTTLS
   [RFC3207] session it enables the server to use a certificate with the
   identity that the client expects, as is recommended in [RFC7817] and
   is required for SMTP MTA-STS [RFC8461].  When a client presents a
   name using SNI, the server can log the name using the "sni"
   additional-registered-clause.

   IANA is requested to add one new entry to the additional-registered-
   clauses registry:

      "sni" - indicates the Server Name Indication was used.

      "name" - the name provided by SNI.  It has the syntax of a Domain
      Name.



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3.  The Port Number clause

   When several sending mail hosts send mail from behind a Network
   Address Translator (NAT), often the only way to tell which host sent
   the is to look up the sending port number in the NAT's logs.  The
   server can log the sending port number using the "port" additional-
   registered-clause.

   IANA is requested to add one new entry to the additional-registered-
   clauses registry:

      "port" - indicates the mail client's port number

      "number" - the client's port number.  It has the syntax of an
      integer.

4.  IANA Considerations

   IANA is requested to update the Registration Procedure for the
   Additional-registered-clauses registry to Expert Review.  The IESG
   will appoint the expert(s).

4.1.  Guidance for Designated Expert

   The Designated Expert is expected to check that a proposed
   Additional-registered-clause has a specification that is stable and
   detailed enough to implement the clause and interoperate.  The Expert
   should ensure that the clause name is reasonably related to the
   information it represents, that the contents of the clause are well-
   defined, and that any external references it depends on, e.g., a
   vocabulary of keywords, are stable and well-defined.

5.  Security Considerations

   E-mail is subject to a vast range of threats and abuses.  In a few
   circumstances, a new Additional-registered-clause might disclose
   information to a recipient that was otherwise unavailable.  On the
   other hand, better logging usually makes it easier to diagnose
   failures and attacks.

   If the SNI information in a STARTTLS negotiation is logged, it may
   make it easier to determine the recipient(s) of the message if they
   are not already logged in trace headers.








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6.  References

6.1.  Normative References

   [RFC3207]  Hoffman, P., "SMTP Service Extension for Secure SMTP over
              Transport Layer Security", RFC 3207, DOI 10.17487/RFC3207,
              February 2002, <https://www.rfc-editor.org/info/rfc3207>.

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              DOI 10.17487/RFC5321, October 2008,
              <https://www.rfc-editor.org/info/rfc5321>.

   [RFC6066]  Eastlake 3rd, D., "Transport Layer Security (TLS)
              Extensions: Extension Definitions", RFC 6066,
              DOI 10.17487/RFC6066, January 2011,
              <https://www.rfc-editor.org/info/rfc6066>.

6.2.  Uninformative References

   [RFC7817]  Melnikov, A., "Updated Transport Layer Security (TLS)
              Server Identity Check Procedure for Email-Related
              Protocols", RFC 7817, DOI 10.17487/RFC7817, March 2016,
              <https://www.rfc-editor.org/info/rfc7817>.

   [RFC8461]  Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A.,
              and J. Jones, "SMTP MTA Strict Transport Security (MTA-
              STS)", RFC 8461, DOI 10.17487/RFC8461, September 2018,
              <https://www.rfc-editor.org/info/rfc8461>.

Appendix A.  Change history

   02 to 03  Add port numbers.  What the heck.

   01 to 02  Take out ESNI clause to prevent downref.

   00 to 01  Add new ESNI clause.  Fix many typos.

   00 New draft

Author's Address











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   John Levine
   Taughannock Networks
   PO Box 727
   Trumansburg, NY  14886

   Phone: +1 831 480 2300
   Email: standards@taugh.com
   URI:   http://jl.ly











































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