SMTP Require TLS Option
RFC 8689

Received changes through RFC Editor sync (created alias RFC 8689, changed abstract to '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, by default, prioritized over security.  This document describes an SMTP service extension, REQUIRETLS, and a message header field, TLS-Required.  If the REQUIRETLS option or TLS-Required message header field 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 recipient-side policy mechanisms such as MTA-STS and DNS-Based Authentication of Named Entities (DANE) be ignored when relaying a message for which security is unimportant.', changed pages to 16, changed standardization level to Proposed Standard, changed state to RFC, added RFC published event at 2019-11-27, changed IESG state to RFC Published)