Update to Additional Registered Clauses in SMTP Received Headers
draft-levine-additional-registered-clauses-01

Network Working Group                                          J. Levine
Internet-Draft                                      Taughannock Networks
Updates: 5321 (if approved)                             January 25, 2019
Intended status: Standards Track
Expires: July 29, 2019

    Update to Additional Registered Clauses in SMTP Received Headers
             draft-levine-additional-registered-clauses-01

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 two new clauses for Server Name Indication (SNI).

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 29, 2019.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  The Server Name Indication clause . . . . . . . . . . . . . .   2
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Guidance for Designated Expert  . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   3
     5.2.  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 two
   new clauses 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.  When a client presents an encrypted
   name using ESNI [ESNI] the server can log the fact that the client
   did so.

   IANA is requested to add two new entries 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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      "esni" - indicates whether Encrypted Server Name Indication was
      used.

      "yorn" - the literal string "yes" or "no".

3.  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).

3.1.  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.

4.  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 exchanged in
   encrypted form [ESNI] a mail server would generally not have access
   to the SNI, and can only log that ESNI was used.

5.  References

5.1.  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>.

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   [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>.

5.2.  Uninformative References

   [ESNI]     Rescorla, E., Oku, K., Sullivan, N., and C. Wood,
              "Encrypted Server Name Indication for TLS 1.3", draft-
              ietf-tls-esni-02 (work in progress), September 2018.

   [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

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

   00 New draft

Author's Address

   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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