qgreylist is a 'lite' version of greylisting. It greylists only by
source IP address, mainly because it's written as a wrapper for
qmail-smtpd so has no other information available. For home and
small office use this works nearly as well.

Homepage:
https://web.archive.org/web/20170701214830/https://jonatkins.com/page/software/qgreylist/
