A program which examines incoming emails and rejects those which the user has indicated that he or she is not interested in. There are a number of criteria for rejecting an email, ranging from the name of the sender to the occurrence of certain words in the header or body of the email. For example, a mail filter for spam includes words such as dollar, offer, make, and money. Mail filters can be found as part of a sophisticated mail reader or can be stand-alone programs. See also bozo list.