def new_message_accepted(self, msg):
raise NotImplementedError<EOL>
This method is called when a new message was accepted by the server.
        Now the MTA is then in charge of delivering the message to the
        specified recipients. Please note that you can not reject the message
        anymore at this stage (if there are problems you must generate a
        non-delivery report aka bounce).

        There will be one deliverer instance per client connection so
        this method may does not have to be thread-safe. However this method
        may get called multiple times when the client transmits more than one
        message for the same connection.