Interesting. Meanwhile, does SMTP have something like HTTP Strict Transport Security? It would be nice for an impartial party to compile a list of mail servers

Interesting. Meanwhile, does SMTP have something like HTTP Strict Transport Security? It would be nice for an impartial party to compile a list of mail servers that pledge to accept encrypted connections, and for sending MTAs to treat it as a connection failure if the destination is on that list but doesn't appear to support encryption.