The logic to perform cross-forest move mailboxes has changed considerably and you'll need to do a lot of extra steps to prepare for the move mailbox. Microsoft release a script that helps you with these pre-requisites such as synchronizing the msExchMailboxGUID.
This sample Windows Powershell script supports the first part by synchronizing mailbox users from an Exchange 2003, Exchange 2007 and Exchange 2010 source forest to Exchange 2010 target forests as mail enabled users. This is accomplished by synchronizing Active Directory attributes in the online help and by calling the Update-Recipient cmdlet to turn the target objects into mail enabled users.
You can download the sample Windows Powershell script from the Prepare for Online Mailbox Move [ http://go.microsoft.com/fwlink/?LinkId=177882 ] download page. For more information about using and writing scripts, see Scripting with the Exchange Management Shell [ http://technet.microsoft.com/en-us/library/bb123798.aspx ] .
To run this sample script, you need the following:
- a source forest running Exchange 2003, Exchange 2007 or Exchange 2010, where the mailbox currently resides
- a target forest with Exchange 2010 installed, where the mailbox will be moved to
For more information on cross-forest move mailbox have a look at this technet article: