deepOfix is a mail server in a box licensed under the GPL. deepOfix is LDAP-driven with an OpenLDAP server, brings SpamAssassin and ClamAV support with it and offers Webmail and the ubiquitious SMTP, POP3 and IMAP services. I spent an hour test driving this software and it looks good. A clean web interface to manage the lot, shell access for root and optionally for individual users offer what a small business would need. Note to self: keep an eye on this project.