SpamAssassin is the most widely used open source Spam identification application. It uses a wide variety of local and network tests to identify spam signatures, making it hard for spammers to craft messages that might get around less advanced Spam filters.
Your email server comes pre-configured to destroy spam with the industryleading SpamAssassin software. No config needed!
If you would like more information on SpamAssassin, visit the project's official website.