Exchange 2003 owa connection during Exchange 2007 transition

Hi all -
We are currently moving through an Exch 03 - 07 transition.
We have 3 mail servers in the Exch 03 environment in 3 different AD sites that handle owa access. We will be implementing an Exch 07 environment that includes 1 CAS, 1 HUB and 2 mailbox servers (in a CCR configuration) in our data center. We will not have any mailboxes on the cluster initially. We will not have an Edge server in place; per recommendations we will be implementing an ISA server in the DMZ for the OWA/RPC/ActiveSync traffic to route through.
So I have 3 questions:
1. If CAS is up, but the external mail relay is not pointed to it, everything continues to route to the Exch 03 organization, just as it does now, correct?
2. After we bring up the CAS server and start routing the email from our host relay service to the CAS server, and given that we do not immediately have mailboxes set up in the Exch 07 environment, is OWA access going to remain as is for all the Exch 03 users until we actually get OWA access going to CAS?
3. Once OWA access routes through ISA and points to CAS, do we simply take down the current OWA connections, and will CAS automatically do the routing to those servers for OWA?
See attached diagram
Visio-F-P-Exchange07-Interim-Ste.pdf
SJ53Asked:
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NpatangCommented:
First Question , you are correct: Till then the external mail is not pointed its not going to perform any issues.
Changing the host Relay servive doesn't affect OWA until the URL you use for the OWA point to the CAS BOX from ISA. ( I think you get the Answer for question 3 as well )
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SJ53Author Commented:
Thanks! I was able to get additional confirmation on this from a consultant we are working with, so I feel much better about the transition plan.
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