MTA-STS DNS record is malformed
ATTENTIONWhat it means
The record at _mta-sts.example.com is not a valid announcement, so senders never look for your policy file. The policy you are hosting is being ignored.
How to fix it
Publish exactly: v=STSv1; id=<a value you change on every policy edit>. The id must be 1, 32 alphanumeric characters.
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 3.1. 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_TXT_INVALID
Every fix on this site is yours to implement. If you would rather someone did it, I take this work directly.