We are currently running Exchange 2003 and are planning to upgrade to 2010. We are doing one role at a time (slowly over a few weeks) to make sure we don't break anything. I need a back out plan for the CAS portion. If for some reason the CAS breaks something after we repoint our DNS entries and VIPs, is there a way to revert back to the 2003 environment? Can we just change the DNS entry back to the original as it was before?
Is there anything that installs with CAS that makes this impossible? We have lots of users using ActiveSync as well so I'm curious if CAS somehow magically takes over a portion of the traffic beyond a simple DNS/url redirect.