MTA-STS policy file is malformed
URGENTWhat it means
The policy file is served but does not parse (the offending value). Senders discard a policy they cannot read, so TLS is not enforced despite everything being in place.
How to fix it
The file needs version: STSv1, a mode:, one mx: line per mail host, and max_age:. Each on its own line, no leading spaces.
Check your own domain
This page describes the condition. To find out whether your domain has it, run the MTASTS test or the full checkup, which examines every record at once.
Understand it properly
This page covers one condition. For the whole picture, MTA-STS, defined, or start at the Health Library.
Where this comes from
We judge this against RFC 8461 section 3.2. Every finding on this site cites the specification behind it so you can check the work rather than take our word for it.
Other MTASTS conditions
MTASTS_POLICY_INVALID
Every fix on this site is yours to implement. If you would rather someone did it, I take this work directly.