SMTP MTA Strict Transport Security (MTA-STS)
draft-ietf-uta-mta-sts-11

Document Type Active Internet-Draft (uta WG)
Last updated 2017-11-16 (latest revision 2017-11-09)
Replaces draft-brotman-mta-sts
Stream IETF
Intended RFC status Proposed Standard
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Document shepherd Leif Johansson
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Send notices to Leif Johansson <leifj@sunet.se>
Using TLS in Applications                                    D. Margolis
Internet-Draft                                                 M. Risher
Intended status: Standards Track                             Google, Inc
Expires: May 12, 2018                                    B. Ramakrishnan
                                                             Yahoo!, Inc
                                                              A. Brotman
                                                            Comcast, Inc
                                                                J. Jones
                                                          Microsoft, Inc
                                                        November 8, 2017

              SMTP MTA Strict Transport Security (MTA-STS)
                       draft-ietf-uta-mta-sts-11

Abstract

   SMTP Mail Transfer Agent Strict Transport Security (MTA-STS) is a
   mechanism enabling mail service providers to declare their ability to
   receive Transport Layer Security (TLS) secure SMTP connections, 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
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 May 12, 2018.

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
   (http://trustee.ietf.org/license-info) in effect on the date of

Margolis, et al.          Expires May 12, 2018                  [Page 1]
Internet-Draft                   MTA-STS                   November 2017

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     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 . . . . . . . . . . . . . . . . . .   8
     3.4.  Policy Selection for Smart Hosts and Subdomains . . . . .   9
     3.5.  MX Certificate Validation . . . . . . . . . . . . . . . .  10
   4.  Policy Application  . . . . . . . . . . . . . . . . . . . . .  10
     4.1.  Policy Application Control Flow . . . . . . . . . . . . .  11
   5.  Reporting Failures  . . . . . . . . . . . . . . . . . . . . .  11
   6.  Interoperability Considerations . . . . . . . . . . . . . . .  12
     6.1.  SNI Support . . . . . . . . . . . . . . . . . . . . . . .  12
     6.2.  Minimum TLS Version Support . . . . . . . . . . . . . . .  12
   7.  Operational Considerations  . . . . . . . . . . . . . . . . .  12
     7.1.  Policy Updates  . . . . . . . . . . . . . . . . . . . . .  13
     7.2.  Policy Delegation . . . . . . . . . . . . . . . . . . . .  13
     7.3.  Removing MTA-STS  . . . . . . . . . . . . . . . . . . . .  14
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     8.1.  Well-Known URIs Registry  . . . . . . . . . . . . . . . .  14
     8.2.  MTA-STS TXT Record Fields . . . . . . . . . . . . . . . .  15
     8.3.  MTA-STS Policy Fields . . . . . . . . . . . . . . . . . .  15
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
     9.1.  Obtaining a Signed Certificate  . . . . . . . . . . . . .  16
     9.2.  Preventing Policy Discovery . . . . . . . . . . . . . . .  16
     9.3.  Denial of Service . . . . . . . . . . . . . . . . . . . .  17
     9.4.  Weak Policy Constraints . . . . . . . . . . . . . . . . .  18
     9.5.  Compromise of the Web PKI System  . . . . . . . . . . . .  18
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