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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.


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Take a read of this blog post from the MS Exchange team about getting Exchange 2010 to proxy ActiveSync requests to Exchange 2003. – Ben Pilbrow Mar 14 '11 at 20:51
You can revert/rollback just by reversing your DNS and firewall changes, that should be fine. – Paul Cunningham Mar 15 '11 at 0:48
up vote 1 down vote accepted

The CAS will not; reverting the DNS entries should do the trick (as long as your users aren't yet on new servers' mailboxes, of course). Be careful about the Hubs; as soon as you link a send connector you may have outbound mail trying to use it.

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Thanks, this is what we were wondering. We're taking a tip-toe approach to the install by doing one role at a time since the organization is so large. – liquid101 Mar 15 '11 at 11:53

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