Exchange 2010 subdomain configuration

Question

Let me explain my situation as this is strange and I am baffled and new to this organization.  I work for a University and we have tons of email servers on campus.  Everyone has a  @university.edu email and account, but all the departments
/ colleges under the main university do their own thing.
So that means I work for @dpt.university.edu and we have our own Exchange 2010 server.  Oh, and @university.edu is a Linux free something or another.
We have been delegated the sub domain and manage our own dns they are secondary.  We have only 1 smtp on people's accounts (dpt.university.edu) but when people here send mail it is @university.edu.  When people respond it goes to @university.edu. 
I have been having people configure a forward rule from university to dpt.university.edu and that works.
So what am I missing?  Where else should I be looking?  I have not had to manage exchange since 2003.
Thanks
tim

Answer 1

So that is a bit confusing.  I am sure main campus has an edge transport for their site, but we are not setup as a forest or affiliated what so ever.  Interestingly enough you send mail to dpt.university.edu the full mail name is displayed. 
So we have 1 edge transport here at the dpt.university.edu, I cannot tell too much about central campus.  I feel like this could be a dns issue, but our dpt.university.edu has the mail subdomain with the mx record pointing to the smtp server. 
I will admit I did not set this up, but it bugs me that I cannot figure it out.
Tim
PS HUH? I looked at the link and things look setup correctly not sure what more I need to do.