Greylisting is of marginal utility at best. The only thing that it accomplishes is slowing down all of your regular mail. SPF/DK don't slow down your mail and a

Greylisting is of marginal utility at best. The only thing that it accomplishes is slowing down all of your regular mail. SPF/DK don't slow down your mail and actually do a pretty decent job of getting rid of unsophisticated mail spammers, but do nothing for "marketers". "Spammers don't retry" was something that happend in the 1990s, they figured out they could fill their MTA queues full and get actual delivery a long time ago. There may be proxy mail spammers out there that don't retry still, but they're amateurs at best, the pros have all this stuff figured out. Don't kid yourself that you're wasting their time, your server is a small speck in the ocean of mailservers, and what they really care about is delivery to all of the big MSPs like gmail/yahoo/msft/rr/etc. That all said, if it makes you happy to feel like you're "messing with spammers", I'm all for it! I derive great satisfaction in running my own boxes for vanity so I'm hardly one to deny that feeling to anyone else :)