A situation arose in my company where I had to move an email address from an existing user to a newly created user. Here's what I did:
1. Created a new mailbox and user object
2. Renamed the email address on the existing account
3. Added the email address that was on the old mailbox to the newly created mailbox.
4. Restarted the transport service and waited for over 12 hours.
So at the moment mail from outside exchange goes to the correct mailbox, but mail sent from inside the organistion goes to the old mailbox. Any ideas on how to fix this?