help fighting spam

[Jon Bjorn Njalsson]

Greetings

I have been recieving tons of spam with random subject like "how's your
ramrod", "+ 5 inches or money back" etc, all of them containing URL to
random sites, but all sites resolve to the same ipaddress 216.40.47.17.

I have written over 30 rules based on the domain name but I was
wondering isn´t it possible to have SA do a lookup of the domain name,
get the ipaddress, then lookup the ipaddress and check if that ipaddress
is listed in some rbl and score acordingly ?

regards
Jon