Allow users to change their expired passwords via OWA.

One common scenario is that user's passwords expire when they are out of town or remote, and they are unable to change their password.  Starting with Exchange 2007 Service Pack 3 (and 2010/2013), users have the ability to change their expired password via OWA if you set a registry key to turn this functionality on.

 - On your Exchange CAS server, open regedit and navigate
to HLKM\SYSTEM\CurrentControlSet\Services\MSExchange OWA

 - Create a DWORD value called ChangeExpiredPasswordEnabled, and set the value data to 1.  If it already exists, simply change the value data to 1.

 - Close regedit, open the command prompt and type 'iisreset /noforce' to restart IIS.