I'm installing 2 new physical servers from scratch. My main server will be Windows Server 2012 R2 Essentials with AD, DNS, DHCP and Anywhere Access enabled and configured. My second server will be my Exchange Server 2013 in Windows Server 2012 R2 Standard. I've read the MS TechNet articles on this setup which state that the CAS role should be installed on the "Internet facing" server. I'm not clear on weather I should install Exchange Server 2013 with the mailbox role and CAS role together on the same mail server or install CAS on my main server and only the mailbox role on the mail server. Please clarify.