milter manager is a flexible and low administrative cost anti-spam system that can be used with MTAs that support milters like Sendmail and Postfix. It provides an effective solution by combining a range of existing milters.
The SPSmtpGate is a transparent anti-spam SMTP proxy server. SPSmtpGate has support for the Sendmail version 8 Milter (mail filter) protocol. SPSmtpGate is easy to set up because it requires only minor changes to the configuration of your mail transfer agent.