A program which prevents certain emails from being read. A major use for such software is for the identification and disposal of spam. It can also be used for screening off harmful emails from children. An email filter rejects emails using a large number of criteria, including the length of the email, keywords in the header of the email, the sender of the email, the size of the email, and the occurrence of certain words in the body of the text. There are many email filters, ranging from the simple ones found in the major email programs to sophisticated stand-alone utilities. See also anti-spam software and Bozo list.