Do i need Windows Server 2012 CAL's if only accessing the Exchange Server?

I am about to implement a deticated Exchange 2013 enterprise server, with windows 2012 server its going to be a central server for 250 users, this means the server is on a central location and users are connecting remotely to this server.

The clients will only be accessing trough outlook , i understand i need 250 Exchange 2013 User CAL's, but do i also need need Windows Server 2012 CAL's ?

thanks in advance !