can't send mail back and forth between debian & local domain

["Richard E. Hawkins" <hawk@hawkins.cba.uni.edu>]

I can send mail from  my debian box to anywhere except my local domain.

The debian box is hawkins.cba.uni.edu, and any mail to any account at 
uni.edu yields the result,

  hawkins at uni.edu: loses; [USER] 550 '<hawkins@uni.edu>' 
<hawkins@(nodomain)> not matched: (ERR_100) unknown user.
post: 1 addressee undeliverable

Message not delivered to anyone.



--