Thanks to Dave Howe for pointing out this newly released hotfix. With the release of KB.883652, it’s now possible to script cross-site mixed-mode moves based on the Exchange 2003 SP1 feature. Before applying this hotfix, if you are doing scripted moves with the MoveMailbox method of the IMailboxStore interface and you select a destination in a different site you will get an error like:
This mailbox cannot be moved to a different Exchange Server 2003 administrative group while in a mixed Exchange 5.5/Exchange Server 2003 Organization.
Error code: -1056749031
With the hotfix in place, a new parameter (FCrossAG) is exposed that allows you to specify that the move should be cross-site. Also included with this hotfix is exposure of a parameter that allows you to control the Skip Bad Items feature of Exchange 2003 mailbox moves (IMaxBadItemsToSkip).