If the correct ports are open on the Exchange server...( i believe that its simply port 80 and 81 But i might be wrong)...Simply act as if you were inside the network and add an Exchange server. and instead of typing the server name.....type its external Ip address, when you type your account name into the prompts, and click Check Name, you should see your server name pop up, and your full Account name fill in....you should now be connected to your exchange server from outside the office