Returns obsolete valid messages after operation.
        @type domain: str
        @rtype: dict

def get_obsolete_messages(self, domain):
        """
        Returns obsolete valid messages after operation.
        @type domain: str
        @rtype: dict
        """
        if domain not in self.domains:
            raise ValueError('Invalid domain: {0}'.format(domain))

        if domain not in self.messages or \
            'obsolete' not in self.messages[domain]:
            self._process_domain(domain)

        return self.messages[domain]['obsolete']