MTA-STS report
also: TLSRPT report, TLS Report
A security report generated by mail servers documenting their enforcement of MTA-STS (Mail Transfer Agent Strict Transport Security) policies, including policy violations and delivery failures.
MTA-STS is a standard that allows domain owners to publish policies requiring mail servers to use encrypted TLS connections when delivering email. An MTA-STS report is a JSON-formatted message that receiving mail servers send back to the domain owner's report@_mta-sts.example.com inbox, documenting compliance successes and failures.
These reports help domain administrators identify when other mail servers fail to connect securely to their domain, or when the published MTA-STS policy itself is unreachable. For example, a report might indicate that Mail Server X attempted delivery but couldn't validate the STARTTLS certificate, or that the policy file was temporarily unavailable.
Reports are aggregated daily and sent in TLSRPT (TLS Reporting) format, allowing administrators to monitor the effectiveness of their mail security policy and debug connectivity issues between MTAs.