Spam Filter

A spam filter is software that automatically identifies and separates out unwanted bulk email, commonly by scoring each incoming message against rules or statistical models trained on known examples of spam. Programmer Paul Graham popularized a practical statistical approach using Bayesian probability in his 2002 essay A Plan for Spam, which influenced many of the spam filters built into email services afterward. Modern spam filters combine content analysis, sender reputation and machine learning to keep the great majority of unwanted email out of a user's inbox before it is ever seen.