Exchange 2010 and 2007 co-exsistance- mailboxes on 2010 are still getting emails throuhg 2007 CAS

We have exchange 2010 and 2007 environment. The mailboxes on 2010 are getting emails through exchange 2007 CAS array. Why is that?  Second, is there some way to force 2010 mailboxes traffic to come through 2010 CAS array. We also have barracuda appliances ( if they are cause of this behavior--don't know)