SMTP MTA Strict Transport Security (MTA-STS)
RFC 8461
Document | Type |
RFC - Proposed Standard
(September 2018; Errata)
Was draft-ietf-uta-mta-sts (uta WG)
|
|
---|---|---|---|
Authors | Daniel Margolis , Mark Risher , Binu Ramakrishnan , Alex Brotman , Janet Jones | ||
Last updated | 2020-08-08 | ||
Replaces | draft-brotman-mta-sts | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Reviews | |||
Stream | WG state | Submitted to IESG for Publication | |
Document shepherd | Leif Johansson | ||
Shepherd write-up | Show (last changed 2018-03-06) | ||
IESG | IESG state | RFC 8461 (Proposed Standard) | |
Action Holders |
(None)
|
||
Consensus Boilerplate | Yes | ||
Telechat date | |||
Responsible AD | Alexey Melnikov | ||
Send notices to | Leif Johansson <leifj@sunet.se> | ||
IANA | IANA review state | Version Changed - Review Needed | |
IANA action state | RFC-Ed-Ack |
Internet Engineering Task Force (IETF) D. Margolis Request for Comments: 8461 M. Risher Category: Standards Track Google, Inc. ISSN: 2070-1721 B. Ramakrishnan Oath, Inc. A. Brotman Comcast, Inc. J. Jones Microsoft, Inc. September 2018 SMTP MTA Strict Transport Security (MTA-STS) Abstract SMTP MTA Strict Transport Security (MTA-STS) is a mechanism enabling mail service providers (SPs) 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 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/rfc8461. Margolis, et al. Standards Track [Page 1] RFC 8461 MTA-STS September 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 (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. Margolis, et al. Standards Track [Page 2] RFC 8461 MTA-STS September 2018 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. Related Technologies . . . . . . . . . . . . . . . . . . . . 5 3. Policy Discovery . . . . . . . . . . . . . . . . . . . . . . 5 3.1. MTA-STS TXT Records . . . . . . . . . . . . . . . . . . . 6 3.2. MTA-STS Policies . . . . . . . . . . . . . . . . . . . . 7 3.3. HTTPS Policy Fetching . . . . . . . . . . . . . . . . . . 10 3.4. Policy Selection for Smart Hosts and Subdomains . . . . . 11 4. Policy Validation . . . . . . . . . . . . . . . . . . . . . . 11 4.1. MX Host Validation . . . . . . . . . . . . . . . . . . . 12 4.2. Recipient MTA Certificate Validation . . . . . . . . . . 12 5. Policy Application . . . . . . . . . . . . . . . . . . . . . 12 5.1. Policy Application Control Flow . . . . . . . . . . . . . 13 6. Reporting Failures . . . . . . . . . . . . . . . . . . . . . 13 7. Interoperability Considerations . . . . . . . . . . . . . . . 14 7.1. SNI Support . . . . . . . . . . . . . . . . . . . . . . . 14 7.2. Minimum TLS Version Support . . . . . . . . . . . . . . . 14 8. Operational Considerations . . . . . . . . . . . . . . . . . 15 8.1. Policy Updates . . . . . . . . . . . . . . . . . . . . . 15 8.2. Policy Delegation . . . . . . . . . . . . . . . . . . . . 15 8.3. Removing MTA-STS . . . . . . . . . . . . . . . . . . . . 16 8.4. Preserving MX Candidate Traversal . . . . . . . . . . . . 17 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 9.1. Well-Known URIs Registry . . . . . . . . . . . . . . . . 17 9.2. MTA-STS TXT Record Fields . . . . . . . . . . . . . . . . 17 9.3. MTA-STS Policy Fields . . . . . . . . . . . . . . . . . . 18 10. Security Considerations . . . . . . . . . . . . . . . . . . . 18 10.1. Obtaining a Signed Certificate . . . . . . . . . . . . . 18 10.2. Preventing Policy Discovery . . . . . . . . . . . . . . 19 10.3. Denial of Service . . . . . . . . . . . . . . . . . . . 19 10.4. Weak Policy Constraints . . . . . . . . . . . . . . . . 20Show full document text