"Other folk have been using whitelist based filtering, which is based on the idea that you keep a 'whitelist' of known email addresses, and filter unknown senders into a folder for occasional scrutiny. After a some bad spam weather, I decided to try combining this technique with content-based filtering, so that genuine messages from unknown addresses would also be separated from the most obvious spam. This document is mostly about the use of RDF to exchange whitelist data, so that we minimise false positives in whitelist based filtering."