Migration from Pop3 Server to Exchange

Hello All
I have set up Exchange 2007 and configured it with one mailbox for the time being as i have a pop3 program taking care of mail.
I want to migrate users accross slowly so i have set up a forward for my mail to my exchange mailbox

the only problem is when i mail anyone on the same domain as me it looks for the reciepient locally as it shoudl do.

Is there a way to tell exchane to forward the mail for all non existant users back to the SMTP so i can more users over slowly and still allow internal communication???
Thanks in advance?