Transition from Exchange 2003 to Exchange 2010

Posted on 2014-01-06
Medium Priority
Last Modified: 2014-03-07

Our current Exchange environment has only one Exchange 2003 server and we would like to transition to Exchange 2010.

The Exchange 2010 implementation will have three servers with the roles as below.


I have tested the transition process successfully in a test environment but wanted to know whether there would be any client connection or mail flow issues with the current Exchange 2003 environment if I were to introduce the first Exchange 2010 CAS/HUB server with no further configuration for the time being.

An extract from training material provided to me by Learning Tree International suggests the following within quotes.

“In order for the CAS server to handle Exchange 2003 mailbox connections, the CAS server must not hold the Mailbox server (MB) role.

-Servers that hold CAS and MB roles can only access Exchange 2010 mailboxes”

Could someone also kindly verify this statement?

Thank you.
Question by:bestway_it
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LVL 63

Accepted Solution

Simon Butler (Sembee) earned 75 total points
ID: 39759066
It is no longer considered best practise to separate the roles out. Therefore I would deploy all three roles on all of the servers.
As soon as you have your first CAS role holder in place, you should configure an RPC CAS Array. Furthermore clients will start to use it for Autodiscover.


Not really sure what the statement that you have posted is on about, as to the best of my knowledge, for OWA access, Exchange 2010 can only redirect, not proxy the traffic.
The usual co-existence method is to have two URLs - an Exchange 2010 URL and an Exchange 2003 Legacy URL.

This guide from TechNet should be the one that you follow:


Author Comment

ID: 39759238
Hello Simon,

Thank you for your quick reply.

Two of the servers will eventually be having all three roles. The one server with only the MBX role will be used for journaling.

Due to the Learning Tree International statement, I was going to install EXCHSRV1 with just CAS/HUB and EXCHSRV2 with MBX until all Exchange 2003 mailboxes were moved over to EXCHSRV2.

EXCHSRV3 would be worked on last.

Are you suggesting that there would be no issues with current client connectivity and mail flow following installation of EXCHSRV1 and EXCHSRV2 with all three roles during the Exchange 2010 installation wizard?

The only expected issue with Outlook 2007 and higher clients will be end users receiving certificate prompts until the RPC CAS ARRAY is configured and required SAN certificates registered.

Other than that, mail flow and mailbox connectivity should not be effected.

I would like to have the Exchange 2010 servers with their respective roles in place and achieve successful backups before moving incoming/outgoing emails and mailboxes to them.

Does this sound correct?
LVL 63

Expert Comment

by:Simon Butler (Sembee)
ID: 39759343
I completely missed it was only 50 points. I don't usually touch 50 point questions.
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Author Comment

ID: 39759392
Wow, I have never heard that before.

What kind of points are you looking to work with?
LVL 11

Expert Comment

ID: 39761896
Remember you are trying to perform a transition.

Install only one 2010, move 1 mailbox and test everything, owa, autodiscover, mobile devices, etc.; Then remove your 2003 and then install the other server for your other needs.

It is not recommended to transition to a complicated or more elaborated environment.

As to my knowledge... keep it simple and it will be easy to manage in case of problems.

Author Comment

ID: 39762057

Yes, I plan to take things one step at a time which is why the main query was whether it would be okay to perform an Exchange 2010 installation (on one server) with just the CAS/HUB roles and no further configuration without having an impact on the existing Exchange 2003 environment.

By impact I am referring to mail flow and client connectivity issues (MAPI, AS and OWA).

My understanding thus far is that I should go ahead and install all three roles (CAS/HUB/MBX) on the first Exchange 2010 server and the only issue that may arise is Outlook 2007 and above clients receiving certificate warnings every time they open the application.

Following installation of the first Exchange 2010 server and taking care of Internal DNS entries and RPC CAS Array, I intend to generate a Certificate Request for a SAN certificate and submit it to one of the online Certificate Authorities.

I will only work on directing (incoming/outgoing) mail flow through the RPC CAS Array (which for the time being will point to one of the CAS servers until we install hardware load balancers) once I know that the certificates are in place.

All remaining tasks will be completed once the above is in place and fully functional.

Could you please confirm this to be correct.

Thank you.
LVL 11

Assisted Solution

hecgomrec earned 75 total points
ID: 39762243
Yes, this should be ok.

You can just go to your certificate authority and request your actual key to include the new name of the server.  Most of the time your cert. can include up-to 5 names.

So when installing your 2010 you can install your actual certificate you just re-key with this server name.

While you are in transition, if you have no problems with the connector between 2010 and 2003, your AD will find the mailbox in either server for the specific user regardless the GUI, OWA, Outlook, iOS, Android, etc....

Just, remember to try with one account first, if possible yours not to affect the rest of the users.  Then, move more but non critical that use mobile devices and test, test and test until you start moving everyone to the new server.

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