We did this for my old company, with Cyrus IMAPd and spamassassin. The mail directories are regular directories on the server, and then it's just a cronjob. I r

We did this for my old company, with Cyrus IMAPd and spamassassin. The mail directories are regular directories on the server, and then it's just a cronjob. I regret that we didn't think of Google's priority inbox, which would have been trivial to implement!