spam blocker

Spam blocker is the phrase used to describe a type of computer software that is designed to prevent spam, or unsolicited e-mail sent in bulk to a large number of recipients, from going directly to the inbox of your e-mail client.

Also known as spam filters, spam fighters or anti-spam utilities, spam blocking software has evolved from simply watching for keywords in the subject line of messages to using advanced technology like Bayesian and similar heuristic filters to help identify spam through suspicious word patterns or word frequency.

See All About Software: categories of applications software explained.
Also see "Getting Rid of Spam" and "All About Spam, Spim and Spit" in the Did You Know section of Webopedia.