Kainaw's Journal: Why not dig?

Ferriera, my anti-spam project, uses 'dig +short' to get a list of the IP addresses of the URLs in emails. As a good side-effect, it also returns the proper domain name for many URLs. It has been working wonders for me, blocking a good 95% of all spam without any false-positives. But, everyone tells me that it is the absolute dumbest idea in the world because dig takes too long to lookup all those IP addresses. So, I have to wonder... What if dig times out on three or four IP addresses in a row? What if it takes a good six minutes to parse one email? What happens? Am I supposed to believe that my email server will suddenly crash, or explode, or take on an evil form of artificial intelligence and start raising killer bees in the Napa Valley region to put a thorn in the side of the major wine producers of America? Since this is the reason I am always given for NOT doing an IP lookup, I want to know why I shouldn't do it.