I had one exchange user that somehow ended up with duplicates of all their folders. Not only did they have an Inbox1 but they had a Tasks1, Calendar1 etc. These empty duplicate folders because the default so I created a new mailbox, exmerged all the users messages and appointments from the old account to the new mailbox.
I then disconnected both the new temporary user from the new mailbox and the problem users from his problem mailbox, then reconnected the problem user with the new mailbox.
He can now log on to Outlook and see all the proper folders with no duplicates. He can send mail okay and can receive mail from the outside which is delivered via a POP connector.
The problem is sending messages to this new user internally - for some reason, now when anyone tries to send him an email, we get a "Delivery Status Notification (Failure)" NDR from Exchange. What's going on here?