This should be OK althought I haven't done it myself. The same process we go through to get a mailbox after it's moved between Excahnge home stores should apply here - we'll try to open the mailbox with our cached MailboxDN handle and if that fails we fall back to ask AD to give us another handle to the users' mailbox and then log in again. After you bring Unity up we need to log into everyone's mailbox to monitor for MWIs and notification events so this process should happen in the background. If folks call in to check messages before that's complete they'll experience a short delay while we attempt to get their mailbox handle.
Short sotry, AD always knows where your mailbox is and we have the DirectoryID of the user in AD and if we can't open it using the cached copy of the handle we know how to get another one so it should be fine.
