Like I said, I can't really test this, so you may have to search around for some of these options, but on the setup page (if you already have the account set up, as opposed to being stuck in the account setup wizard, you should be able to modify the existing config from Tools→Account Settings) you should see something like "More Settings". Then, maybe under a "Connection" tab, there will be a checkbox for something like "Connect to Microsoft Exchange using HTTP". Then there should be more config options related to that (an "Exchange Proxy Settings" button, maybe?). You should be given a place to enter the URL you use to access it from your web browser. There are probably a bunch of other options that you might have to play around with.