Do we have to purchase a license for an Exchange 2013 server that just has the Client Access Server role (CAS) installed?

According to the Exchange Server 2013 Licensing page, you need a license for each instance of the server software.  

http://office.microsoft.com/en-us/exchange/microsoft-exchange-server-licensing-licensing-overview-FX103746915.aspx

If we do have to purchase a license for a server that just has the CAS role installed, would it be only the Standard edition?

Thanks.

 

Hi,
Every installation of Exchange Server (=instance of the server software as the license pages refered to) needs a license yes and since a CAS Role doesn't hold any mailboxes...Standard Edtion would be the best choice.