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

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Last updated 2019-07-30
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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.

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

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   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
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   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-
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