Is there some free software mail server for Linux (at least IMAP + SMTP), offering also some web interface and good spam filtering, which is specialized for small MX (in the DNS) sense, and few email accounts. (e.g. less than 40 email accounts, and one or a few thousand emails per day, including spam). Actually I have two DNS domains on the same VPS (at OVH in France).
Ideally, I would like a single software package doing all that. (and of course, my goal is to avoid gmail).
(I don't mind some configuration work, and I am using Linux since 1994)
All the SMTP + IMAP servers I know (exim, postfix, sendmail, dovecot) are optimized for large traffic and many accounts; I would like something more integrated, but reliable. And SPAM filtering is done thru addons, all this being difficult to set up.
Some promising solution might be IredMail (which does not work on Ubuntu 15.04)
PS my VPS is Ubuntu 15.04 (but I could change it to Debian 8 Jessie).