We are currently migrating from Exchange 5.5 to 2003. We have successfully installed the main Exchange 2003 into the first of our two Exchange 5.5 sites. However, we do not appear to be able to create a mailbox using ADUC on the Exchange 2003 server as yet. Is this expected behaviour, and we need to create the mailbox in 5.5, then migrate it until we get rid of Exchange 5.5? Or is there an underlying issue I need to resolve?