Cleartext Considered Obsolete: Use of Transport Layer Security (TLS) for Email Submission and Access
RFC 8314

Document Type RFC - Proposed Standard (January 2018; Errata)
Last updated 2018-04-16
Replaces draft-newman-email-deep
Stream IETF
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Reviews
Stream WG state Submitted to IESG for Publication
Document shepherd Leif Johansson
Shepherd write-up Show (last changed 2017-09-29)
IESG IESG state RFC 8314 (Proposed Standard)
Consensus Boilerplate Yes
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Responsible AD Alexey Melnikov
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IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack
Internet Engineering Task Force (IETF)                          K. Moore
Request for Comments: 8314                                Windrock, Inc.
Updates: 1939, 2595, 3501, 5068, 6186, 6409                    C. Newman
Category: Standards Track                                         Oracle
ISSN: 2070-1721                                             January 2018

  Cleartext Considered Obsolete: Use of Transport Layer Security (TLS)
                    for Email Submission and Access

Abstract

   This specification outlines current recommendations for the use of
   Transport Layer Security (TLS) to provide confidentiality of email
   traffic between a Mail User Agent (MUA) and a Mail Submission Server
   or Mail Access Server.  This document updates RFCs 1939, 2595, 3501,
   5068, 6186, and 6409.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8314.

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

Moore & Newman               Standards Track                    [Page 1]
RFC 8314         Use of TLS for Email Submission/Access     January 2018

Table of Contents

   1. Introduction ....................................................3
      1.1. How This Document Updates Previous RFCs ....................3
   2. Conventions and Terminology Used in This Document ...............4
   3. Implicit TLS ....................................................5
      3.1. Implicit TLS for POP .......................................5
      3.2. Implicit TLS for IMAP ......................................5
      3.3. Implicit TLS for SMTP Submission ...........................6
      3.4. Implicit TLS Connection Closure for POP, IMAP, and
           SMTP Submission ............................................7
   4. Use of TLS by Mail Access Servers and Message Submission
      Servers .........................................................7
      4.1. Deprecation of Services Using Cleartext and TLS Versions
           Less Than 1.1 ..............................................8
      4.2. Mail Server Use of Client Certificate Authentication .......9
      4.3. Recording TLS Ciphersuite in "Received" Header Field .......9
      4.4. TLS Server Certificate Requirements .......................10
      4.5. Recommended DNS Records for Mail Protocol Servers .........11
           4.5.1. MX Records .........................................11
           4.5.2. SRV Records ........................................11
           4.5.3. DNSSEC .............................................11
           4.5.4. TLSA Records .......................................11
      4.6. Changes to Internet-Facing Servers ........................11
   5. Use of TLS by Mail User Agents .................................12
      5.1. Use of SRV Records in Establishing Configuration ..........13
      5.2. Minimum Confidentiality Level .............................14
      5.3. Certificate Validation ....................................15
      5.4. Certificate Pinning .......................................15
      5.5. Client Certificate Authentication .........................16
   6. Considerations Related to Antivirus/Antispam Software
      and Services ...................................................17
   7. IANA Considerations ............................................17
      7.1. POP3S Port Registration Update ............................17
      7.2. IMAPS Port Registration Update ............................18
      7.3. Submissions Port Registration .............................18
      7.4. Additional Registered Clauses for "Received" Fields .......19
   8. Security Considerations ........................................19
   9. References .....................................................20
      9.1. Normative References ......................................20
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