Daemon which provides TLS client policy for Postfix via socketmap, according to
domain MTA-STS policy. Current support of RFC8461 is limited:

  - MTA-STS policy overrides DANE TLS authentication against RFC 8461, 2.
  - Daemon lacks some minor features:
    - Fetch error reporting.
    - Fetch ratelimit (but actual fetch rate partially restricted with
      cache_grace config option).

Server has configurable cache backend which allows to store cached STS policies
in memory (internal), file (sqlite), Redis database (redis) or in PostgreSQL
database (postgres).