Setting Outlook Web App as the default page in Exchange 2010 CAS server makes life easier for end users. It saves them the effort to type the precise OWA address, and of course the error messages when they mistype it or forget to use secure socket layer (SSL) connection.
Using https redirection for the Default Web Site and forwarding all requests to the OWA directory might seem as an easy approach but it brings up two problems. First, changes in the root directory settings are propagated automatically to all subfolders and affect all Exchange virtual directories. Cleaning up the mess and restoring the default settings of the subdirectories should be done manually. Second, the permissions of the web.config file, generated under the OAB directory prevent local Outlook users as well as remote Outlook Anywhere users from downloading the Offline Address Book – adjusting the security settings of this file is required.
In this Screencast, we demonstrate how to configure OWA in Exchange 2010 CAS server as the default web page. The Exchange 2010 server is running on Windows Server 2008 R2, and we are dealing with IIS7.5.
For your convenience, we have provided the text file with the config file which we are using in the demo .

Step 1 In the first step, we demonstrate how to redirect https://yourexchangeserver to the OWA page. This approach is easier to implement, and is suitable for companies which do not allow HTTP access to the internal Exchange 2010 CAS server.

Step 2 In this step, we add the option to redirect HTTP requests to the default Exchange 2010 page, to the encrypted OWA address. Again, the main goal is to keep the changes to the default IIS 7.5 and Exchange 2010 CAS configuration minimal, while preserving the security settings. The corporate firewall should be configured to allow requests on TCP port 80 to the internal exchange CAS, in this case.