EX5.5 on DMZ and internal network!

Does anyone know how to setup inbound SMTP on the DMZ Ex5.5 server and outbound SMTP from the internal Ex5.5 server?
I would like to setup my SMTP inbound stops at the Ex5.5 DMZ server (any mails are transferred inside over the site connector), outbound SMTP from internal Ex5.5 sends out directly.
Please help us out and thanks for your time.