On Tue, Feb 14, 2006 at 01:10:29PM +1300, Craig Whitmore said:
I have been playing around with greylisting recently on a couple of test domains and it works pretty well (reduces the number of spam coming from malwared machines who don't retry sending their spam by over 90% before any spam checkers get to it), but I've noticed a number of real mail NZ servers not knowing what a 451 SMTP message is, and they treat it like a fail and they don't send the message again. (Yes I know I can whitelist good known NZ SMTP Serversto not Greylist from them)
If anyone else has tried greylisting before , or has any comments on it, let me know.
We've been using greylisting here for the last six months, and it's made a huge difference to the amount of noise that the downstream spam filters have to deal with. I've had to whitelist one external mail server, and a couple of internal ones, but all in all, I'm well pleased with the results. It's particularly useful to have running over mailman owner addresses to reduce the crap that arrives there. I would set your timeout to be really low - 15 seconds would be as effective as 30 minutes, as far as I can see. Cheers Si