RFC 8689: SMTP Require TLS Option

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…

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Outgoing relationships (24 related RFCs)

Normative reference — RFC 2119: Key words for use in RFCs to Indicate Requirement Levels
Normative reference — RFC 8174: Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words
Normative reference — RFC 5234: Augmented BNF for Syntax Specifications: ABNF
Normative reference — RFC 4033: DNS Security Introduction and Requirements
Normative reference — RFC 5322: Internet Message Format
Normative reference — RFC 4034: Resource Records for the DNS Security Extensions
Normative reference — RFC 4035: Protocol Modifications for the DNS Security Extensions
Normative reference — RFC 5321: Simple Mail Transfer Protocol
Normative reference — RFC 6125: Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)
Normative reference — RFC 7525: Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)
Normative reference — RFC 3207: SMTP Service Extension for Secure SMTP over Transport Layer Security
Normative reference — RFC 3461: Simple Mail Transfer Protocol (SMTP) Service Extension for Delivery Status Notifications (DSNs)
Normative reference — RFC 5248: A Registry for SMTP Enhanced Mail System Status Codes
Normative reference — RFC 7672: SMTP Security via Opportunistic DNS-Based Authentication of Named Entities (DANE) Transport Layer Security (TLS)
Normative reference — RFC 8314: Cleartext Considered Obsolete: Use of Transport Layer Security (TLS) for Email Submission and Access
Normative reference — RFC 8461: SMTP MTA Strict Transport Security (MTA-STS)
Informative reference — RFC 3501: INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1
Informative reference — RFC 5598: Internet Mail Architecture
Informative reference — RFC 1939: Post Office Protocol - Version 3
Informative reference — RFC 4880: OpenPGP Message Format
Informative reference — RFC 5228: Sieve: An Email Filtering Language
Informative reference — RFC 8551: Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 Message Specification
Informative reference — RFC 6409: Message Submission for Mail
Informative reference — RFC 2033: Local Mail Transfer Protocol

Incoming relationships (2 related RFCs)

Informatively referenced by — RFC 9525: Service Identity in TLS
Informatively referenced by — RFC 10003: Certificate Management over CMS (CMC): Transport Protocols