Remote Access to Internal Exchange Svr.

My current network is a small NT4 LAN using fast Ethernet. MS Exchange 5.5 is deployed for email. MS Proxy 2.0 is installed on the same server with Exchange for internet connection (using DSL). I need to move Proxy to a different server and allowremote acceess to the network for checking email. Security is an important issue. What is the best strategy for this scenario?
Thank you.