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