I have implemented such policy server: it lookups MTA-STS policy, caches and updates it as RFC 8461 defines.
Github: https://github.com/Snawoot/postfix-mta-sts-resolver PyPI: https://pypi.org/project/postfix-mta-sts-resolver/ Daemon lacks some features required by standard like proactive policy fetch, reporting and ratelimit, but it serves its main purpose - TLS policy discovery. I use it for my personal mailserver. Hope it'll be useful for someone. -- Sent from: http://postfix.1071664.n5.nabble.com/Postfix-Users-f2.html
