I have Exchange 2010 at my main office and have set up a second Exchange 2010 server at another office to provide DR/BC. I am using Database Availability Groups (DAG) to replicate the databases to the remote site. I know that Outlook 2007/2010 can use the SRV records to find AutoDiscover, and therefore find the secondary server if there is a failure.
The question is: can I set up automatic failover for Outlook Web App and ActiveSync clients (specifically the iPhone and iPad)? Will OWA and/or ActiveSync clients use AutoDiscover to find the secondary server, or is there something else I need to do to help these clients reconfigure automatically?
Check this:
http://www.msexchange.org/articles_tutorials/exchange-server-2010/high-availability-recovery/load-balancing-exchange-2010-client-access-servers-using-hardware-load-balancer-solution-part1.html
You could also use a NLB cluster.
Next you configure a CAS Array:
http://blogs.technet.com/b/ucedsg/archive/2009/12/06/how-to-setup-an-exchange-2010-cas-array-to-load-balance-mapi.aspx