Runs in your browser
TLS-RPT checker
Look up the SMTP TLS reporting policy.
The lookup goes from your browser straight to a public service. We never see the domain.
What this checks
SMTP TLS Reporting (TLSRPT) is a DNS record at _smtp._tls.<domain> that asks other mail servers to report back when they fail to deliver mail to this domain over an encrypted connection.
What to look for
A working record needs a rua= address. Without one, a sending server that hits a broken or downgraded TLS connection has nowhere to tell you, and the failure goes unnoticed.
Not the same as MTA-STS
TLSRPT only reports problems; it does not enforce encryption. Enforcement is a separate record, MTA-STS, checked by its own tool.