On the Effectiveness of Pre-Acceptance Spam Filtering

Modern SMTP servers apply a variety of mechanisms to stem the volume of spam delivered to users. These techniques can be broadly classified into two categories: pre-acceptance approaches, which apply prior to a message being accepted (e.g. blacklisting and whitelisting), and post-acceptance techniques which apply after a message has been accepted (e.g. content based signatures). In recent years, pre-acceptance techniques have attracted a lot of attention. In addition to cutting down spam, effective and accurate pre-acceptance filtering is crucial to reducing the load on SMTP servers.