Installing your first Exchange 2010 CAS – Part 3

This is the third, and last, part of the “Installing your first Exchange 2010 CAS” tutorial. In part 1 we discussed migration from Exchange 2003 to Exchange 2010, In part 2 migration from Exchange 2007 to 2010. Today we will discuss the case of mixed Exchange 2003 – 2007 environment.

If you managed to get your Exchange 2003/2007 environment working together then you already know that Exchange 2007 CAS can proxy requests to Exchange 2003 mailbox servers. We also know from part 1 of this tutorial that it is not the case for Exchange 2010.

Right now you have your Exchange 2007 CAS that is internet facing and handling all incoming requests by itself. Basically you should think of this as a combination of part 1 and part 2, one thing is common and it is that the newly introduced Exchange 2010 CAS will be dealing with incoming requests.

For Exchange 2007 Mailboxes

For users to be able to access their mailbox on Exchange 2007 every thing we covered in part 2 of this tutorial still holds true, a quick summary would be

If you have an Exchange 2007 mailbox server in the same Active Directory site

  1. You will need to have an internet facing, or published, Exchange 2007 CAS in the same site.
  2. Exchange 2010 CAS will redirect clients to the ExternalUrl set on your Exchange 2007 CAS
  3. For this to work seamlessly Form Based Authentication should be enabled on the OWA virtual directory of you Exchange 2007 CAS

If you have an Exchange 2007 CAS and mailbox server in a different Active Directory site

  • If ExternalUrl is set on the Exchange 2007 CAS, Exchange 2010 CAS will redirect the clients to it, this redirection is however not automatic, clients presented with a web page containing that URL
  • If ExternalUrl is not set on the Exchange 2007 CAS, Exchange 2010 CAS will proxy the request to the 2007 CAS
  • You can force the 2010 CAS to proxy (instead of redirect) even if the ExternalUrl is set on the 2007 CAS by running the following on your 2010 CAS
  • Set-OwaVirtualDirectory "owa (default Web site)" -RedirectToOptimalOWAServer:$false

For Exchange 2003 Mailboxes
Here also we will use the same concept we discussed in part 1 of this tutorial with the only difference that the Exchange2003Url on the Exchange 2010 CAS will be set to the same as the ExternalUrl set on the Exchange 2007 CAS. So we will be using the Exchange 2007 CAS to access the 2003 mailboxes no matter in which Active Directory site they are.

You shouldn’t forget that, for this redirection to work seamlessly, Form Based Authentication should be enabled on the OWA, Exchweb and Public virtual directories on the 2007 CAS and on the 2003 mailbox server.

I hope you enjoyed this 3 parts tutorial and that I was able to shed some light on how to introduce your first Exchange 2010 CAS to your organization.

Part 1: Installing your first Exchange 2010 CAS in an Exchange 2003 organization
Part 2: Installing your first Exchange 2010 CAS in an Exchange 2007 organization
Part 3: Installing your first Exchange 2010 CAS in a mixed Exchange 2003/2010 organization

I have been working in IT consultancy and solution integration since 1998 and I consider myself lucky to be, one in a few, making a living out of my passion. I am also member of the famous Experts Exchange (profile here) online community where I try my best to share what I have learned along the road.

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