Mail relaying by SMTP auth. (At last! Use mail.artifex.org,
port 587 as your outgoing mail, require TLS, and supply your username
and password – and you can finally send mail without relying on
a gmail account.)
Mail retrieval (IMAP and POP, though POP’s not automatically tested.)
Spam filtering. (Spam goes into spam/, no user configuration
or bogofilter required.)