Greylisting + MS Exchange 2003

I’m using greylisting to filter spam. It works quite well. If you aren’t of the technique this is how it works. Greylisting filters spam by testing the RFC compliance of the server that is trying to send mail to you. RFCs 2821 and 821 describe the meat and potatoes of sending email on the internet. The RFCs both specify that the receiver may tell the sender to queue the message and retry later because the receiver is temporarily out of resources. Greylisting exploits this to sift spam from legitimate email because many Spam sending programs cannot queue mail. As a method of spam detection Greylisting is great because it takes almost no resources on the receiving side to filter. Other methods of filtering are not so resource friendly. I find that Greylisting is rejecting over my inbound 90% of the spam. I used to say that it did this with 0 false positives but after reading these two threads I’m not so sure:

Leave it to Microsoft to rain on the parade.

I’m not going to stop Greylisting. It’s just been too effective at spam removal for me to even consider going without. I’m also aware of several people who are using Exchange to contact me who have not run across this problem. For me the solution to this potential problem is to contact some of the people who I know that are running Exchange and see what their awareness is on this problem.