I recently migrated some mailboxes from one exchange 2003 server (remote) to another 2003 exchange server(local) across a WAN. When trying to configure one of the mailboxes that migrated successfully it would error out saying it was not configured. I made sure replication had run between sites to rule out any DNS or other issues. I then opened the system manager and expanded both servers mailbox stores and ran the cleanup agent on the remote server. I tried to add the test account again and it still said not configured and closed out. I then ran the cleanup agent on the local server and tried to configure it and this time it resolved the local exchange name and was able to open the mailbox in outlook.