Blocking email to specific domains

I am trying to block email to specific domains or email addresses.
How should I best do this using Exchange?

The version is Exchange 2003 w/ (sp2)

Thanks,

You can block IP addresses through settings in the SMTP Virtual Server, and

You can block IP addresses through settings in the SMTP Virtual Server, and
recipient e-mail addresses through settings in Global Settings > Message
Delivery > Sender Filtering.
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Ed Crowley
MVP - Exchange