Exim Error: Sender Domain must Exist

[Sebastian Canagaratna <scanagar@canax2.onu.edu>]

Hi:

   I am using Debian Potato from home and connect by modem to my
   university network using exim. The connection uses DHCP. My machine
   is named sebastian. I can collect, using fetchmail, my mail
   coming to the university post office server, but when I send mail
   to the university or outside, I get the error message; Sender
   domain must exist. My machine is interpreted as sebastian@onu.edu
   which is clearly not recognized as an legitimate machine. I guess
   it recognizes the IP address given to me by the DHCP server, 
   but how do I configure exim to look after this?

   Thanks in advance.

   Sebastian Canagaratna
   Department of Chemistry
   Ohio Northern University
   Ada, OH 45810