I did the following migration: SBS 2003+Exchange+SQL05 from old Raid to new Raid (same Server, HAL - execpt raid-controller & hdds). Everything finde, reinstalled Exchange, backup via ntbackup, reconnected all the users.
User can access, read, delete his emails (pop3-connector to external mailbox).
User can't create any Subfolder within his "Inbox". The Error message is "Can't create folder".