Email prioritization: reducing delays on legitimate mail caused by junk mail

Abstract

In recent years the volume of junk email (spam, virus etc.) has increased dramatically. These unwanted messages clutter up users' mailboxes, consume server resources, and cause delays to the delivery of mail. This paper presents an approach that ensures that nonjunk mail is delivered without excessive delay, at the expense of delaying junk mail. Using data from two Internet-facing mail servers, we show how it is possible to simply and accurately predict whether the next message sent from a particular server will be good or junk, by monitoring the types of messages previously sent. The prediction can be used to delay acceptance of junk mail, and prioritize good mail through the mail server, ensuring that loading is reduced and delays are low, even if the server is overloaded. The paper includes a review of server-based anti-spam techniques, and an evaluation of these against the data. We develop and calibrate a model of mail server performance, and use it to predict the performance of the prioritization scheme. We also describe an implementation on a standard mail server.