After performing a Cross Org mailbox migration, administrators need to enable mail redirection from the source to the target forest. Even though GALSync remains the recommended tool for this purpose, the initial synchronization process can take some time which means that messages queued during the move and messages sent from users in the source forest before the contacts objects were created will NDR.

To address this issue, Exchange 2007 added to Move-mailbox a parameter called SourceMailboxCleanupOptions to determine what "source cleanup" will be done after the move.

For RTM