Trilent Mail Proxy   
http://www.trilent.net

This firewall-friendly mail (SMTP/POP3) proxy enables small network users to access and distribute email via a single Internet connection, eliminating the need for dedicated mail servers. This is an application-level proxy. It enhances network security by enforcing mail protocol rules and offering many security promoting features, such as access control and event logging. Once configured, the proxy works unobtrusively in the background and requires minimal attention. It offers "install-and-forget" operation. The proxy is designed with reliability in mind. Its modular, multi-threaded design and implementation as a Windows service contributes to its superior stability (it carries the "Designed for Windows" logo.) The proxy supports up to 30 concurrent mail connections, offers extensive compliance with Internet standards and includes a simple mail monitor, capable of monitoring mail connections. Note: To run the program you need a free trial registration key from publisher's Website.

No Spam Today! for Servers Freeware   
http://www.byteplant.com

No Spam Today! is an SMTP/POP3 proxy server based spam filter that sits between the internet and your mail server. Incoming mail is accepted from the Internet and checked for spam and viruses. NoSpamToday! uses the award-winning SpamAssassin engine to flag spam mail in the subject line and add a filtering report to spam mails according to your configuration. NoSpamToday! works with products of all vendors of mail client or server software, and also allows simple integration of third-party virus checkers. When installing No Spam Today! you will get: 1. A complete one stop setup routine that installs one of the world's most advanced and thorough spam filters on your server in a matter of minutes. 2. A reliable SMTP/POP3 proxy service software that makes it easy to integrate No Spam Today! into any existing email infrastructure 3. An easy to use Admin Wizard to configure all important settings of No Spam Today! and the SpamAssassin engine 4. Updates, e.g. when new versions of the SpamAssassin engine are released 5. An attachment blocker, and built-in support for third-party virus checkers 6. Free support (commercial licenses only) NoSpamToday! is available as freeware for personal and non-commercial use. Several commercial licenses are available, offering exceptional value at low prices.