A better idea is to list the with thr rbl list. Look at www.mail-abuse.org One known there as an open relay they will be listed and routing their data will have a lot of problems in North America. I am not sure how to list them there, but they have a database and some routers tap into it to disable routing. Very interesting. I had a client in China. His mail servers IP was in the database and from that day on he had a lot of problems with the emails he was sending.
