One of the things that changed overtime from Exchange 4.0 through Ex2K is that you could always access any mailbox with the ServiceExchange service account.
When Microsoft released Ex2K3 they made it a lot harder to get this ‘feature’ to work. Now in Ex2K7 it’s even harder.
No matter what the reason is that you need this ‘feature’, some companies just need it.
Check out the link to find out how you can leverage powershell to make it work: