Managing exchange online with server 2012 Essentials

Hi,<o:p></o:p>

I need to integrate an office 365 account (Exchange online) with server 2012 essentials.  There are 23 email accounts in total but I only need 15 of these users to be able to log on to the server.<o:p></o:p>

Is there a way of keeping them separate without using up the allowance for the server Cals?<o:p></o:p>

Regards,<o:p></o:p>

Dave<o:p></o:p>