"SpamAssassin" Anti-spam has a built in configuration interface for SPAM rules server wide or on a per mailbox basis. Use this add-on and eliminate SPAM.
Spam wastes is a waste of your time and money. The SpamAssassin filter will help you combat this all too common problem and is a flexible tool that allows the user to define what they consider to be Spam and have the filter catch it. No one is making choices for you. The user can add and remove addresses, keywords, and phrases, basically letting the program 'learn' what is Spam and what is not.
SpamAssassin Anti-SPAM Software