When you are using the default OWA configuration you have to specify the “exchange” virtual directory in order to check your email. The URL looks like this: “httpss://mail.mydomain.com/exchange”.
The following screencast demonstrates how to use the main URL: “httpss://mail.mydomain.com” by configuring a redirection to a URL.

New: How to Configure OWA as the Default Web Page in IIS7, Exchange Server 2007

Step 1 Click here to watch the Screencast …