[Exim] stop delivery to local users

I am running exim 4.14 on machine1.msu.edu which has a user named
testuser. When I try to send a message from machine1 to
testuser@??? exim delivers this locally to
testuser@???. Is there a setting I'm missing to make this go
to testuser@???? Right now I'm using the stock configuration
file but I've tried everything I can find in the docs and some that I
didn't.

Thanks,

Tony