I was told that I posted this question to the wrong forum, so I am reposting here:
We are preparing for our migration from our old regular (not Hosted) Exchange 2007 system to our new Hosted Exchange 2010 system (they are in different forests, as apparently a Hosted 2010 server cannot exist in the same forest as regular 2007). I have been reading a Microsoft whitepaper on the migration process (Overview - HMC to Hosted Exchange 2010 Migration Guide version 1.0, published September 2010), and I spotted this note about OWA:
Note: Exchange Product Group researching solution in which Exchange 2010 could proxy connections back to Exchange 2007 for users who haven’t had their mailboxes migrated yet.
One of the biggest hurdles we've been trying to clear is the proxying of connections back to the 2007 Exchange server. Our research so far suggests that it is only possible if we were migrating to regular Exchange 2010, not to Hosted 2010....but this whitepaper is about Hosted 2010, so I gotta ask about it. If this was still being researched back in September of 2010, and it is now 2012, is it possible that a workable proxying method has been created by now? If so, who would I have to contact to get that information? Is there maybe a similar option for Outlook Anywhere and ActiveSync? I really hope it can be done, it would revolutionize this entire process since this is a production 2007 system and some transparency for the users would make this whole transition easier for everyone.....
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In my earlier posting to the incorrect forum, this whitepaper was suggested to me:
http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=28714 (Migrating Exchange From HMC 4 5 to Exchange Server 2010 SP2)
but it covers items (such as migration of Public Folders) that I know do not exist in Hosted 2010, so I wonder how applicable it is to our situation. I really just need to know if it is possible to have regular 2007 and Hosted 2010 coexist enough so that we can use the CAS server on the Hosted forest to communicate with both the 2010 and 2007 Exchange installations, and access users on whichever side contains their mailbox.
Sorry for being so long-winded, I realize I'm probably still stomping all over a bunch of forum conventions in my ignorance, but I don't submit to forums very often...I'll do my best to learn the proper methods, but I'm a real forum noob at this point, and it will show....
A few comments.
If you haven't already started, don't build a new forest using /hosting mode. If you haven't read about this, start here http://blogs.technet.com/b/exchange/archive/2011/10/13/future-of-hosting-mode.aspx
If you have, and want to carry on, then no, I'm afraid you cannot proxy or redirect OWA or Activesync users between forests. You can redirect Outlook Anywhere users, but typically you don't want to split tenant between two forests, it is both very hard to do, and limits functionality severely.
If you have 2007 today, and want to go to 2010, and don't use /hosting, you could stay in the same forest and make your life much easier. It all depends on what you have, and what you are really trying to do.
No joy, no. So no, you can't do forest to forest redirect, and you might also want to get familiar with this document and set of tools: http://blogs.technet.com/b/exchange/archive/2012/02/03/released-migrating-from-exchange-server-2010-in-hosting-mode-to-exchange-server-2010-sp2-whitepaper.aspx
- Proposed as answer by Greg Taylor [msft]Microsoft employee Tuesday, February 21, 2012 7:27 PM