How do I block certain senders in Postfix?

Further to my post a few weeks or so ago, how do I block emails from being accepted by postfix. The emails in particular are from one of 2 different IP addresses. I suppose I could block only those 2, or perhaps the entire range if need be. I read a bit on this in the docs, but am unsure if I should make a "hash" for it, or use canonical, and if so, how. I do have a hash for check_recipient_access which is working great. But I don't know how to block a particular IP address for a sender. I'm running Suse 10.0, mostly standard postfix. Many thanks for any pointers. Jim Flanagan