[krylon]

I see. ;-)

I hope you succeed. Filtering out bad actors via DNS is a good idea, you will have to be very careful about false positives, though. ;-)

I think a similar approach is already being used for mail servers to detect spam... but I am short on details, because the only mail server I have ever taken care of is the Exchange server at work, and Exchange is not all that proactive when it comes to spam.

[jlgaddis]

DNSBLs [0] are very popular. Pretty much anyone running a mail server that accepts connectiona from the public Internet use them -- you have to! I manage several mail servers and I use many different DNSBLs, including one of my own.

The best anti-spam advice I could give WRT your Exchange box (I've managed those too) is to put another box in front of it to handle the spam filtering (Postfix + SpamAssassin + friends in my case, but you have many options), though IIRC even Exchange can directly use these blacklists nowadays.

[0]: https://en.wikipedia.org/wiki/DNSBL