Yes, you read right ! Let me explain : I setup 1 Exch2007 server in our lab, created some mailboxes, then installed Exch2010 servers (CAS/HUB and MBX) to test out migration. Worked great ! Now I was asked to restore the 2007 server from a production backup (where only 2007 servers exist), to simulate the prod environment... But the 2007 server I installed has already been removed and there only remains the 2010 servers in the lab environment. Is it possible to install a 2007 server in this 2010 environement (lab)? Or does the Exchange schema update to 14726 not allow this?

If I get you right, the answer is no. Take a look here: If you have transitioned from Exchange 2007 to Exchange 2010 and the last Exchange 2007 server has already been decommissioned, the answer is again no. You will not be able to install Exchange 2007 at a later time in this organization because it’s now considered a pure Exchange 2010 organization. Exchange Queue & A http://technet.microsoft.com/en-us/magazine/ff394355.aspxMCTS: Messaging | MCSE: S+M

Thanks Jon-Alfred, I was afraid of that. Oh well, I guess I need to create yet another lab environement and restart an AD under 2007 ... Thanks, again ! Thread closed.