The default INFO logs are more oriented towards debugging and can be
a bit too verbose when looking for high-level information.
This patch introduces a new "maillog" package, used to log messages of
particular relevance to mail transmission at a higher level.
This patch adds initial support for SMTPUTF8, which for now consists of just
advertising it.
We support most of it, but sending emails over SMTP requires further work, as
the SMTP courier does not support this yet (it's not in Go's standard
library). That will come in subsequent patches, along with IDNA handling.
https://tools.ietf.org/html/rfc6531.html