This will return a summary record for each message in a project. If
        you specify a category_id, only messages in that category will be
        returned. (Note that a summary record includes only a few bits of
        information about a post, not the complete record.)

def message_archive(self, project_id, category_id=None):
        """
        This will return a summary record for each message in a project. If
        you specify a category_id, only messages in that category will be
        returned. (Note that a summary record includes only a few bits of
        information about a post, not the complete record.)
        """
        path = '/projects/%u/msg/archive' % project_id
        req = ET.Element('request')
        ET.SubElement(req, 'project-id').text = str(int(project_id))
        if category_id is not None:
            ET.SubElement(req, 'category-id').text = str(int(category_id))
        return self._request(path, req)