Domain Admins are able to Spoof any email Address

Hello,

DC setup: Server 2012
Exchange server: Exchange 2013 Standard Version 15.0 (Build 516.32) on Server 2012 Standard

Domain Admins are able spoof any email address. Login as a Domain admin to OWA and they are able to spoof any email address by changing the "from" Field. I have come across about this for Ex 2007 (the link below), but nothing on Ex 2013

http://technet.microsoft.com/en-us/library/bb310792.aspx

Please help me to find a way to remove this. Thanks