Exchange 03 Server with multiple emails

This is a Server/Exchange 03 issue I?m having.

We run a 03 exchange server and own 2 domains (.net, and .org). 1 domain is already set up on the exchange server (.org) and is set to only connect through a private VPN connection for emails.

They want to set up another email system using the other domain they own (.net), but would like it to be a public email system, therefore not using the VPN.

They currently have the local ISP doing their DNS, but I will be changing it to our server.

How would I go about setting this new email service up? Is it as simple as adding a new smtp and pop server to the exchange box, or is there a lot more here than meets the eye?

Many thanks in advance,