I have started my Exchange 2010 install. Been researching this for months but I've obviously missed something as OWA and Activesync were dead this AM. Last night I installed the CAS server. That is the only role I currently have installed. I have not modified any SSL certs, or DNS records, or firewall rules. Existing Exchange 2003 BE and FE remain untouched. But login to 2003 OWA results in HTTP/1.1 503 Service Unavailable. I was under the impression that until I applied the new certificate and modified DNS this would not be an issue. HELP!!!