def get_by_fqdn(fqdn_listname):
    """Return the mailing list with the given name, if it exists.

        :param fqdn_listname: The fully qualified name of the mailing list.
        :type fqdn_listname: str
        :return: the matching mailing list or None if no matching list is
            found.
        :rtype: IMailingList
        """
