So, to set this up for my domain, I have to make a TXT record like this: _mta-sts.example.com. TXT "v=STSv1; id=20180928;" Where id is just a unique identifier for the current version of the STS policy, then I configure a webserver to respond to requests for https://mta-sts.example.com/.well-known/mta-sts.txt that looks like this: version: STSv1 mode: testing mx: mx1.example.com mx: mx2.example.com max_age: 86400 Am…
At this moment there are no MTA-STS support in postfix. But this thread [1] in postfix-users mailing list suggests acceptable solution: use external policy server for MTA-STS discovery. I have implemented such server: package on PyPI [2], source on Github [3]. Works for me.
[1] http://postfix.1071664.n5.nabble.com/MTA-STS-when-td95086.ht... [2] https://pypi.org/project/postfix-mta-sts-resolver/ [3] https://github.com/Snawoot/postfix-mta-sts-resolver