Stop SMTP mail

[David W. McSpadden]

I have an Exchange 2003 Standard sp2 server.
I have some legacy smtp addresses laying around in ADUC of
n...@im_dom1.indianafcu.com.
I would like Exchange to not relay those emails to the Internet.  Just keep
them in house. 
Is there a way to not allow *...@im_dom1.indianafcu.com to relay to the
Internet addresses???