If you run Snow Leopard on your Mac, you can use the Autodiscover feature to connect to your McCombs email.
Instructions (taken from http://www.apple.com/macosx/exchange/):
Just open the Accounts pane in Mail, enter your Exchange user name and password, and check the box to automatically set up your other applications. That’s it. Mail uses the Autodiscover feature in Exchange (if enabled) to grab all the pertinent information from the server and configure your settings.