MSASMTP

MSASMTP, short for Microsoft Advanced Secure SMTP, is a proposed extension to the Simple Mail Transfer Protocol designed to improve security, privacy, and policy control in email transport within Microsoft-centric environments. It aims to preserve backward compatibility with existing SMTP deployments while introducing enhancements to strengthen transport security and policy enforcement.

The protocol is described as backward compatible with existing SMTP, while introducing enhancements such as mandatory or strongly preferred Transport Layer Security (TLS) for server-to-server connections, optional mutual authentication for MTAs, and enhanced support for modern authentication methods. It also supports policy-driven routing and rate enforcement to reduce abuse.

For integrity and authenticity, MSASMTP advocates compatibility with standard signing and authentication mechanisms used in email, such as DKIM, S/MIME, and DMARC, and envisions native negotiation of these capabilities during the EHLO/extended handshake.

As of the latest publicly available material, MSASMTP has not been standardized through formal RFCs and has limited or no official adoption; discussions have appeared in vendor white papers and academic proposals, with no official reference implementations.

Related topics include SMTP, STARTTLS, OAuth for SMTP, DKIM, DMARC, and S/MIME.