Greylite
Greylite is a greylisting solution for qmail. Greylite may be preferred to other greylisting solutions because:
it does not require patching qmail, it is simply plugged in the top of the qmail chain; thus is works smoothly with already-patched installations
it does not depend on bigger RDBMSs like PostgreSQL or MySQL, it is self-contained because it uses sqlite
Greylite is easy to setup and maintain, and it is small and fast.
Visit Greylite to download latest version.