Hi there,
Yes, I know that situation, almost the same problem is when the email accounts need to be migrate to the new server.
Here is the way how to do this: in outlook, add a new account (with the same address, but with a new password) and just, still in outlook, copy e-mails from an old account to the new.
It works, but of course may be time-consuming if there is huge amount of data to send/synchronise
Adam