Spam Assasin is a fantastic tool in reducing spam. Email that Spam Asassin suspects to be spam based on several different algorithms, will be marked as SPAM when you receive it making your life a lot easier and less frustrating when going through email.
Spam Assassin
Spam Assassin is an automated mail filter that uses a wide range of heuristic algorithms on mail headers and message body text to identify "SPAM" (unsolicited email). Once identified, the mail is tagged as SPAM for later filtering using the user's desktop mail client.
Enabling the Spam Box feature will cause all mail marked by Spam Assassin as spam to be delivered to a separate mail box called 'spam'. You must use IMAP or Horde/IMP to check messages that are routed to this box.