SMTP Require TLS Option
draft-ietf-uta-smtp-require-tls-01

Document Type Active Internet-Draft (uta WG)
Last updated 2018-01-16
Replaces draft-fenton-smtp-require-tls
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Internet Engineering Task Force                                J. Fenton
Internet-Draft                                          Altmode Networks
Intended status: Standards Track                        January 16, 2018
Expires: July 20, 2018

                        SMTP Require TLS Option
                   draft-ietf-uta-smtp-require-tls-01

Abstract

   The SMTP STARTTLS option, used in negotiating transport-level
   encryption of SMTP connections, is not as useful from a security
   standpoint as it might be because of its opportunistic nature;
   message delivery is, by default, prioritized over security.  This
   document describes an SMTP service extension, REQUIRETLS, and message
   header field, Require-TLS.  If the REQUIRETLS option or Require-TLS
   message header field is used when sending a message, it asserts a
   request on the part of the message sender to override the default
   negotiation of TLS, either by requiring that TLS be negotiated when
   the message is relayed, or by requesting that recipient-side policy
   mechanisms such as MTA-STS and DANE be ignored when relaying a
   message for which security is unimportant.

Status of This Memo

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   This Internet-Draft will expire on July 20, 2018.

Copyright Notice

   Copyright (c) 2018 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

Fenton                    Expires July 20, 2018                 [Page 1]
Internet-Draft           SMTP Require TLS Option            January 2018

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  The REQUIRETLS Service Extension  . . . . . . . . . . . . . .   3
   3.  The Require-TLS Header Field  . . . . . . . . . . . . . . . .   5
   4.  REQUIRETLS Semantics  . . . . . . . . . . . . . . . . . . . .   5
     4.1.  REQUIRETLS Receipt Requirements . . . . . . . . . . . . .   5
     4.2.  REQUIRETLS Sender Requirements  . . . . . . . . . . . . .   6
       4.2.1.  Sending with TLS Required . . . . . . . . . . . . . .   6
       4.2.2.  Sending with TLS Optional . . . . . . . . . . . . . .   7
     4.3.  REQUIRETLS Submission . . . . . . . . . . . . . . . . . .   7
     4.4.  Delivery of REQUIRETLS messages . . . . . . . . . . . . .   8
   5.  Non-delivery message handling . . . . . . . . . . . . . . . .   8
   6.  Mailing list considerations . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
     8.1.  Passive attacks . . . . . . . . . . . . . . . . . . . . .  10
     8.2.  Active attacks  . . . . . . . . . . . . . . . . . . . . .  10
     8.3.  Bad Actor MTAs  . . . . . . . . . . . . . . . . . . . . .  10
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   10. Revision History  . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Changes since -00 Draft  . . . . . . . . . . . . . . . .  11
     10.2.  Changes since fenton-03 Draft  . . . . . . . . . . . . .  11
     10.3.  Changes Since -02 Draft  . . . . . . . . . . . . . . . .  11
     10.4.  Changes Since -01 Draft  . . . . . . . . . . . . . . . .  12
     10.5.  Changes Since -00 Draft  . . . . . . . . . . . . . . . .  12
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     11.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   The SMTP [RFC5321] STARTTLS service extension [RFC3207] provides a
   means by which an SMTP server and client can establish a Transport
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