def is_banned(email):
    """Check whether a specific email address is banned.

        `email` must be a text email address; it cannot be a pattern.  The
        given email address is checked against all registered bans, both
        specific and regular expression, both for the named mailing list (if
        given), and globally.

        :param email: The text email address being checked.
        :type email: str
        :return: A flag indicating whether the given email address is banned
            or not.
        :rtype: bool
        """
