>  POP3 Authenticated Relaying

CommuniGate Pro
A mail transport agent that supports users rules, routing, filtering, aliasing, mail relay rules, anti-spam and more.

Exim
A mail transport agent with options for verifying incoming sender and recipient addresses, for refusing mail from specified hosts, networks or senders, and for controlling mail relaying.

Postfix
A secure, modular (multiple components) and easy-to-configure MTA.