I have Exchange 2010 SP3 with three servers in two separate sites. We originally designed with two servers and a single mailbox/CAS server in each site and DAG. All active databases are in the same site. To do maintenance or failover everyone would get the new CAS server when their mailbox failed over, and we would often times have to modify DNS for the CAS arrays because older Android clients didn't know how to fail over properly. We have now added a second mailbox server in the main site and I am thinking about how to add the CAS role quickly without requiring a hardware load balancer. My thought is to add the CAS role to the second server, and then just change DNS to point to one server or the other as required for doing maintenance or emergencies. I know that it isn't automated failover, and it isn't load balanced, and I am totally okay with that. I am just looking for a way to be less disruptive when I need to do maintenance on a server. Has anybody tried this, or know of why it would or wouldn't work? Eventually I would like to get Kemp. I know not to do round robin DNS.