The statistical technique is known as the Bayesian technique and its use for spam was first described by Paul Graham in his article A Plan For Spam. Gary Robinson, in his weblog Rants, suggests some refinements for improved discrimination between spam and ham. Bogofilter's primary algorithm uses the f(w) parameter and the Fisher inverse chi-square technique that he describes.
Bogofilter is run by an MDA script to classify an incoming message as spam or ham (using wordlists stored by BerkeleyDB). Bogofilter provides processing for plain text and HTML. It supports multi-part MIME message with decoding of base64, quoted-printable, and uuencoded text and ignores attachments, such as images.