SMTP MTA Strict Transport Security (MTA-STS)
draft-ietf-uta-mta-sts-03

Document Type Active Internet-Draft (uta WG)
Last updated 2017-02-15
Replaces draft-brotman-mta-sts
Stream IETF
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Using TLS in Applications                                    D. Margolis
Internet-Draft                                                 M. Risher
Intended status: Standards Track                             Google, Inc
Expires: August 19, 2017                                 B. Ramakrishnan
                                                             Yahoo!, Inc
                                                              A. Brotman
                                                            Comcast, Inc
                                                                J. Jones
                                                          Microsoft, Inc
                                                       February 15, 2017

              SMTP MTA Strict Transport Security (MTA-STS)
                       draft-ietf-uta-mta-sts-03

Abstract

   SMTP Mail Transfer Agent Strict Transport Security (SMTP STS) is a
   mechanism enabling mail service providers to declare their ability to
   receive TLS-secured connections and an expected validity of
   certificates presented by their MX hosts, and to specify whether
   sending SMTP servers should refuse to deliver to MX hosts that do not
   offer TLS with a trusted server certificate.

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 19, 2017.

Copyright Notice

   Copyright (c) 2017 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

Margolis, et al.         Expires August 19, 2017                [Page 1]
Internet-Draft                   MTA-STS                   February 2017

   (http://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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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Related Technologies  . . . . . . . . . . . . . . . . . . . .   3
   3.  Policy Discovery  . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  MTA-STS TXT Records . . . . . . . . . . . . . . . . . . .   4
     3.2.  MTA-STS Policies  . . . . . . . . . . . . . . . . . . . .   5
     3.3.  HTTPS Policy Fetching . . . . . . . . . . . . . . . . . .   6
     3.4.  Policy Selection for Smart Hosts  . . . . . . . . . . . .   6
   4.  Policy Validation . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  MX Matching . . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  MX Certificate Validation . . . . . . . . . . . . . . . .   7
   5.  Policy Application  . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  MX Preference . . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Policy Application Control Flow . . . . . . . . . . . . .   8
   6.  Operational Considerations  . . . . . . . . . . . . . . . . .   8
     6.1.  Policy Updates  . . . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  10
   10. Appendix 1: Domain Owner STS example record . . . . . . . . .  11
     10.1.  Example 1  . . . . . . . . . . . . . . . . . . . . . . .  11
   11. Appendix 2: Message delivery pseudocode . . . . . . . . . . .  11
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     12.2.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   The STARTTLS extension to SMTP [RFC3207] allows SMTP clients and
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