MTASTS-MX-MISMATCH
An MX host is not listed in the MTA-STS policy
What it means
In enforce mode senders refuse MX hosts that do not match an mx: line.
How to fix it
- 1Add the host (or a wildcard pattern) to the policy and bump the policy id in the DNS record.
Re-check after the change
DNS changes can take up to the record's TTL to be seen; use Re-run on the result page to bypass our 10-minute cache.