This is a little feature request:
I kindly suggest to allow each user to set up own Mail Connector. Otherwise the root user will allways know the users password for the external mail (e.g. gmx, yahoo),
I I had a wish, I would put it on the same side, where a user can log in an changs his password.
Perhaps consider the POP3 proxy instead of the POP3 connector. That way the connection is controlled by the end user, and as a (possible) benefit, the user does not need an account in NS.