Greylisting anti-spam method, initial reference implementation and tools.
Greylisting is an email anti-spam technique developed by Evan Harris starting around 2003. This repository contains the original reference proof-of-concept implementation for Sendmail along with some work-in-progress and testing tools.
While this codebase hasn't been in active development for many years, the methods used have been adapted into add-ons for, or integrated into many other email systems, and has dramatically reduced the quantity of received email spam for many users around the globe. The benefits seen by systems/users employing its techniques continue to be effective even today.
The project was previously hosted at http://projects.puremagic.com/greylisting/ and used cvs. Along the way it was migrated to svn, and finally to git. The code repository now resides on Github at https://github.com/eharris/greylisting/ although there is still some documentation and links available at the original puremagic.com URL.