Exchange 2003 to 2010 Migration - External Users / OWA


I am in the process of migrating an Exchange 2003 server onto Exchange 2010 on a 2003 Server based domain. A plan is written but I have a question regarding how external users are going to be connected during the transition and how it is best set this up,  which I hope someone could help with?

For information:
The Exchange server is to have the 3 standard roles on one system.
At present our external users connect via
Our mobile phone users connect in with the exchange setup option pointing to
We have an external IP address that the firewall Nats to our internal exchange server.

My questions relating to this are:

When I start the install process of 2010 there is a section "Configure Client Access Server External Domain" - Enter the domain name you will use with your external Client Access servers"
I believe I tick the Client Access server role will be internet facing. For the Domain do I add in the current 2003 ?

Once this is setup, how will I ensure that the external users will still receive mail on their devices and webmail will continue to work?

I have read about the setting and adding an addition external IP address that points to the new 2010 webmail address. If this is the best way to do it, could someone please explain this and what is the process to do it?

Thanks in advance for any help!

Phil AskeyAsked:
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Jamie McKillopIT ManagerCommented:

This article will take you step-by-step through the transition process. You must use the URL during the transition. The reason for this is that Exchange 2010 cannot proxy request to Exchange 2003. Those request must be redirected to the legacy URL.


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Phil AskeyAuthor Commented:
Hi Jamie,

Thanks for the reply. I will take a look through the document!
To get me started, in relation to the setup of Exchange 2010, during the section : Configure Client Access Server External Domain" - Enter the domain name you will use with your external Client Access servers" do I add in our current address?

I would like to start the install and if this is something that will not effect the current exchange setup ( users going to the current webmail address on 2003 until I make the change over to legacy.webmail )  am I right that I'm ok to progress?


Jamie McKillopIT ManagerCommented:
Yes, you can go ahead and install Ex2010. You would use your current external domain name. Later in the process you will change your DNS records to point this domain name to the external IP of your Ex2010 server and legacy will point to the external IP of the Ex2003 server.

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Phil AskeyAuthor Commented:
Thanks for the reply,sorry for the delay in my getting back to you.

I will press on with the install. Can I just ask that this process is correct?

1. At present external IP points to the on 2003 exchange
2. Change the 2003 address to
3. Add a second external ip address and point it to
4. Change the firewall to point traffic from to the 2003 Exchange server
5. Change the firewall to point traffic from to the new 2010 Exchange server.

So at that point anyone connecting to will be routed to the 2010 server and if their mailbox is not located on 2010 it would forward the request to 2003.

Thanks again,

Jamie McKillopIT ManagerCommented:
That is correct.  All your client traffic will hit 2010 first. If the mailbox is still on 2003, the 2010 server will send the client a redirect to legacy.

Phil AskeyAuthor Commented:

Just want to say thanks very much for the help. I feel much better prepared to start the migration.


Phil AskeyAuthor Commented:
Excellent help. Thanks very much.
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