Effectiveness of Greylisting

I have now implemented Greylisting on many mail sites, from small, to the largest being the mailhosts for the University of Alberta (@ualberta.ca). Generally, mail volume in terms of smtp sessions is reduced by 50 to 65%, sometimes more

The current sample I'm showing you pieces of has roughly 850 000 connections to the greylister over a 36 hour period. During that time about 600,000 smtp sessions were processed by the mail servers.

This reduction can vary of course, depending on how big of a target your site is.

Common Call: "Mail is Broken!" (People get scared when they don't get spam)