Postfix - Mail Trasfer Agent
Cluebringer / Policyd - Postfix policy server
ClamAV - Antivirus
SpamAssassin - AntiSpam
Amavisd - interface between Postfix and SpamAssassin, ClamAV
Dovecot - Mail Delivery Agent: POP3/POP3S, IMAP/IMAPS, Managesieve service
OpenLDAP / MySQL - user database
Roundcube - Web Client accessible from any modern browser
Sogo - Groupware: Calendar, Events, Tasks
Fail2ban - scans log files and bans addresses that indicate malicious connection
Awstats - Apache and Postfix log analyzer