Nice to know poste.io is using the same stack for building email server I am running for a few years already. It's Haraka SMTP server, Dovecot imap server, rspamd for spam filtering and roundcube for accessing messages through the web.
Poste.io ~ complete mail server
Full featured solution for your Email server. Native implementation of last anti-SPAM metods, webmail and easy administration included.poste.io