def _dispose(mlist, msg, msgdata):
    """Dispose of a single message destined for a mailing list.

        Called for each message that the runner is responsible for, this is
        the primary overridable method for processing each message.
        Subclasses, must provide implementation for this method.

        :param mlist: The mailing list this message is destined for.
        :type mlist: `IMailingList`
        :param msg: The message being processed.
        :type msg: `email.message.Message`
        :param msgdata: The message metadata.
        :type msgdata: dict
        :return: True if the message should continue to be queued, False if
            the message should be deleted automatically.
        :rtype: bool
        """
