Milter-greylist

Consider also cutting down on the length of time you greylist for. If someone doesnt return in 3 days, screw em. They are either coming from a broken mta, or a bot. Originally we greylisted for 5 days and this caused problems due to the size of the db. Since cutting that down to 2 or 3 days depending on circumstance, we have not had any problems at all. Definitely utilize whitelists as suggested by Matt+, as they definitely make the process much more bearable.