For TLS over UDP there's DTLS [0] which is probably still problematic for your use case since it still requires the typical TLS handshake.
337 karma · joined March 29, 2013
Is a TCP mode planned? This would be useful for networks where outbound UDP isn't allowed. (hotel wifi, other public wifis)
Do you plan to add automatic key rollover/expiry?
If you are running postfix as your mail server, you could use something like [0] (or write your own solution, utilizing a database or whatever, of course).