Outlook Anywhere Scenario

I have the following scenario:

An exchange server behind a router which connects via pop3 connectors to an external Email server with popsecure. In essence this exchange server is not “Live”.

Presently people can connect easily on LAN and via VPN, but I need users to connect directly without VPN, is this possible? Can anyone show me the steps taking into consideration this server is actually hosting domain emails.

Thanks