I want to be able to use the Exchange 2010 OWA with mailboxes on an Exchange 2007 server.

I want to maintain my mailboxes on the 2007 server and maintain my 2007 HUB/CAS role. My setup is all Windows 2008 x64 servers, 3 Exchange 2007 servers (2 mailbox servers (CCR Active/Passive clustering) and 1 HUB/CAS server).

My goal is to maintain the current environment and have all the mailboxes on 2007, maintain the 2007 HUB/CAS for mail flow and for mobile phone access (2010 is still buggy with some mobile platforms) and have a NEW Exchange 2010 CAS server that only acts as a web portal for mail (the 2010 OWA blows away the 2007 OWA as you are not required to use IE to get real features). This will run on a separate internal server and use a separate hostname from the inside and outside.

Right now I have everything running, the 2007 servers and the 2010 with ONLY the CAS role installed. My problem right now is when I access the 2010 OWA and log in, it opens up the mailbox using the 2007 version of OWA.

So with all that said, is what I am trying to do possible?

I did find It is possible to use the Exchange 2010 web client with an Exchange 2007 mail server? as a relevant post but with no real help except a link I have already read over in my few hours of research into this.

Any help is appreciated.

3 Answers 3


From the playing around i have done i don't think you can view 2007 mailboxes using CAS2010 unless it proxies to a CAS2007. I have found this which seems to say the same thing:

CAS 2010 can only open 2010 mailboxes; it cannot connect to 2003 and 2007 mailboxes. The only time CAS2010 will do anything OWA related with 2007 is if the user's mailbox lives in a non-internet facing AD site and only has CAS2007 boxes in that AD site. When this happens the CAS2010 box in the Internet facing AD site will proxy to CAS2007, which in turn opens the 2007 mailbox. In this one particular case you'll have to copy the CAS2007 binaries to the CAS2010 server for this to work.


This also seems to confirm that it can't be done: http://social.technet.microsoft.com/Forums/en-US/exchange2010/thread/96d63d71-c536-4dab-a401-f26c425c29c9

Sorry i couldn't provide a solution.

  • Thanks, thats what I thought but I just didn't want to believe it! Jul 1, 2010 at 15:47

No, it is not possible.


2010 cannot proxy for OWA on 2007, it redirects. It does proxy transparently for imap, pop, activesync and RPC, however.

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