The "official" log line format is (as of right now at least):
"[socket] [protocol] [user/host-ID] [! if error]message"
Hopefully I can remember that when I add new log messages.

Also setting the protocol to SMTPS, POP3S, SEND/TLS, when appropriate and
passing it around to pretty much any function that can log a message.
Added debug-level log output when the mail sever is sending message body text
(every 100 lines).