MTA-STS is in testing mode
MINORWhat it means
mode: testing means senders report TLS failures but deliver anyway. That is the correct first step, and it protects nothing on its own.
How to fix it
Once your TLS reports come back clean for a couple of weeks, change the policy to mode: enforce.
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 5. 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_MODE_TESTING
Every fix on this site is yours to implement. If you would rather someone did it, I take this work directly.