I set up a new domain and added a user to that domain. When the new user was unable to get mail, I decided to stop and restart Dovecot. The problem now is that Dovecot will not start up. The error is:
Failed to start Dovecot :
Starting Dovecot Imap: Error: Both mail_location and default_mail_env set. Use only one of them.
Fatal: Invalid configuration in /etc/dovecot.conf