[ILUG-BOM] relay deny to authenticated users

Hi,

I just realized that uu.net (appear so me to be an ISP) has many spamers are their clients. I am wondering what is the solution to this. If a spammer will signup for a account from uu.net then he can authenticate himself and send spams to many people. How can uu.net stop this? It appears to me that uu.net is listed as a spaming domain (sorry for this slang language but I do not have the proper term for this) and mails from this domain are not accepted if we disable the mail delivery from blacklisted domains. How can I as a sysadmin make sure that uu.net spams are not welcomed but genuine users from uu.net are no problems. Thanks in advance.

Bye.