One of my Exchange requirements is to allow ActiveSync from the outside but no other Exchange services. It has worked well to create an additional IIS site, create an new virtual directory (New-ActiveSyncVirtualDirectory) on a separate port, and NAT/port change at the firewall for both Exchange 2007 and later 2010. Exchange 2013 has some different frontend/backend IIS sites and creating a third site on a different port gives an IIS error using Admin Center to make Virtual Directory URL changes on any of these boxes. Functionality is returned when the third IIS site is stopped. The new IIS site is on a CAS only box.
Has anyone used a separate IIS site for ActiveSync and gotten this to work in Ex2013? I was thinking of setting up a new CAS box and trying to remove the other virtual directory as a test.