Glossary · Security and privacy
MTA-STS
A policy, published at a well-known URL and announced in DNS, telling sending servers that mail to this domain must use TLS to the named mail exchangers.
What MTA-STS means
A policy, published at a well-known URL and announced in DNS, telling sending servers that mail to this domain must use TLS to the named mail exchangers. It closes the downgrade attack that plain SMTP allows; testing mode reports, enforce mode refuses, and TLS-RPT is where the reports go.
Where MTA-STS comes up on this site
- DMARC p=none to p=quarantine without losing mail: a guideThe neighbouring pieces, an MTA-STS policy to stop transport downgrade and a TLS-RPT address to hear about it, are described on the trust center ; the single-character bounce that started this work is in its own post .
- Release notes 29 Sep 2026: finding states, sitemap, trustTrust center, terms, refunds /trust is built from the running configuration rather than written about it: the retention table reads the real TTLs (reports 90 days, leads 180, the comment queue 30, Search Console and Business Profile data 400, sessions 12…
Terms this definition uses
Definitions that name MTA-STS
Related terms in Security and privacy
Where an agent, a tool or a page can be turned against its operator, and the controls that limit the damage without proving safety.
Indirect prompt injection · Direct prompt injection · Jailbreak · Data exfiltration · Sensitive information disclosure · Secret leakage · Insecure output handling · Excessive agency · Least privilege · Trust boundary · Input validation · Output validation · Allowlist · Denylist · SSRF · RCE · Credential scope · OAuth scope · API key · Bearer token · mTLS · Rate-limit policy · Audit log · PII · Data minimization · Purpose limitation · Retention period · Data residency · Tenant isolation · Threat model · DMARC · DMARC alignment · SPF · DKIM · TLS-RPT · CAA record · DNSSEC · hard bounce
Questions about MTA-STS
What is MTA-STS?
A policy, published at a well-known URL and announced in DNS, telling sending servers that mail to this domain must use TLS to the named mail exchangers.
Which area of the glossary does MTA-STS belong to?
Security and privacy: Where an agent, a tool or a page can be turned against its operator, and the controls that limit the damage without proving safety.
See it in the full glossary · 668 terms across 19 areas.