This is exactly why we custom built a declude reverse DNS check as well as have been begging SmarterTools to FIX the RDNS lookup check or at least add an option to verify the forward of the reverse.

 

When 74.63.201.23 connects and SM does it's RDNS check, it passes. It should not pass. 74.63.201.23 resolves to 23-201-63-74.static.reverse.lstn.net however a forward check 23-201-63-74.static.reverse.lstn.net resolves to nothing. So that SHOULD fail the RDNS check, but does not.

 

Since we use Declude we wrote a simple .net application that does the reverse and forward lookups resolve and match. I hate doing this at the content level, but since SmarterMail's RDNS check is only halfway, this is our only choice.

Note that this IP is also listed in Spamhaus Zen, so you could also add their RBL check to your spam checks. We've found them to be extremely effective.