SMTP Require TLS Option
draft-ietf-uta-smtp-require-tls-00

Document Type Active Internet-Draft (uta WG)
Last updated 2017-09-05
Replaces draft-fenton-smtp-require-tls
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Internet Engineering Task Force                                J. Fenton
Internet-Draft                                          Altmode Networks
Intended status: Standards Track                          August 7, 2017
Expires: February 8, 2018

                        SMTP Require TLS Option
                   draft-ietf-uta-smtp-require-tls-00

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 prioritized over security.  This document
   describes a complementary SMTP service extension, REQUIRETLS.  If the
   REQUIRETLS option 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 policy mechanisms such
   as SMTP STS and DANE be ignored when relaying a high priority
   message.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on February 8, 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

Fenton                  Expires February 8, 2018                [Page 1]
Internet-Draft           SMTP Require TLS Option             August 2017

   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  The REQUIRETLS Service Extension  . . . . . . . . . . . . . .   3
   3.  REQUIRETLS Semantics  . . . . . . . . . . . . . . . . . . . .   5
     3.1.  REQUIRETLS Receipt Requirements . . . . . . . . . . . . .   5
     3.2.  REQUIRETLS Sender Requirements  . . . . . . . . . . . . .   5
       3.2.1.  Sending with TLS Required . . . . . . . . . . . . . .   5
       3.2.2.  Sending with TLS Optional . . . . . . . . . . . . . .   6
     3.3.  REQUIRETLS Submission . . . . . . . . . . . . . . . . . .   7
     3.4.  Delivery of REQUIRETLS messages . . . . . . . . . . . . .   7
   4.  Non-delivery message handling . . . . . . . . . . . . . . . .   7
   5.  Mailing list considerations . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
     7.1.  Passive attacks . . . . . . . . . . . . . . . . . . . . .   9
     7.2.  Active attacks  . . . . . . . . . . . . . . . . . . . . .   9
     7.3.  Bad Actor MTAs  . . . . . . . . . . . . . . . . . . . . .  10
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   9.  Revision History  . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Changes since fenton-03 Draft . . . . . . . . . . . . . .  10
     9.2.  Changes Since -02 Draft . . . . . . . . . . . . . . . . .  10
     9.3.  Changes Since -01 Draft . . . . . . . . . . . . . . . . .  10
     9.4.  Changes Since -00 Draft . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   The SMTP [RFC5321] STARTTLS service extension [RFC3207] provides a
   means by which an SMTP server and client can establish a Transport
   Layer Security (TLS) protected session for the transmission of email
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