Postgrey
Those are the directions I used to setup an almost complete OpenSource Mail server running NetBSD and pkgsrc.
The Mail server will feature:
E-mail exchange (MX) role on the Internet; E-mail gateway (SMTP) for internal LAN users ; E-mail access (IMAP) for internal LAN users ; Secured (TLS and SASL) access for internal users; Greylisting, RFC check and RBL mail filtering ; Directory (LDAP) for e-mail entries ;Continue reading...