ecureuil
In Configure this server screen on sme7 box (login as admin), nominate the gateway IP of sme 9 server, so the sme 7 can have Internet access.
On the sme 9 server gateway box, you need to setup port forwarding for all services & appropriate ports that are running on the sme 7 server.
On sme 9 for email, you can delegate all mail functions to another mail server ie in your case the sme 7 server.
Please read the FAQ (link at top of forums) & various of the Howtos for all the commands you need to do this.
If you use the delegate mail server command, then you do not need to port forward the mail server ports.