Microsoft Exchange Outlook Web Access - OWA - Can't Log On

I was recently troubleshooting a problem for a client were they couldn't access Outlook Web Access (OWA) from the outside of the network. I turns out the problem was caused by the means of authentication defined in Internet Information Services (IIS) was defined as Windows Integrated Authentication. This allows Windows clients on the Windows domain the ability to login to OWA without a user or password. The authentication is passed to the webserver by Windows. When outside the local network or on a computer not joined to the domain the authentication is not passed.
Solutions:
1. Have the users login using the domainname\username at the login prompt. This is the easiest solution.
2. Using IIS Admin, right click the website properties, click the Directory Security tab, click the Edit button under Anonymous access and authentication control. Add Basic Authentication, click the Edit button and add your Windows domain, and remove the Integrated Windows Authentication check box. There is the warning about passwords being sent in clear text, if that is a concern consider using SSL.