Moving mailboxes from Microsoft Exchange Server 2010 to Exchange Server 2007? Consider the following:
- The move process is performed offline, and end-users won’t be able to access their mailboxes during the move.
- You can’t move mailboxes to or from servers running Exchange 2007 Service Pack 1 (SP1) or earlier. The target database must be on a server running Exchange 2007 SP2 or later.
- Perform the move from an Exchange 2010 server by using the move request cmdlets in the Exchange Management Shell. You can’t use the Move-Mailbox cmdlets in Exchange 2007 to move the mailboxes.
- If the mailbox that you’re moving has an archive mailbox associated with it, you must disable the archive before moving the mailbox.
- If you’re moving a mailbox to Exchange 2007, you must disable single-item recovery and purge the Recoverable Items folder. For details, see Clean Up the Recoverable Items Folder.
Reff:
http://technet.microsoft.com/en-us/library/dd638124%28v=exchg.141%29.aspx
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