OWA Exchange 2007 Blocked File Types

Exchange console, CAS server settings, Properties on OWA virtual directory, tabs private and public access.
If you want to add something that is explicitely blocked, you must remove it first from the block list. REMEBER the check the MIME types as well. I was trying to allow XML files and was getting screwed because the mim types text/xml and application/xml were blocked as well.

http://msexchangeteam.com/archive/2007/03/30/437366.aspx