private function swiftEventFilter(TranslatorInterface $translator, $event): string
    {
        switch ($event) {
            case \Swift_Events_SendEvent::RESULT_SUCCESS:
                return $translator->trans('RESULT_SUCCESS');
            case \Swift_Events_SendEvent::RESULT_FAILED:
                return $translator->trans('RESULT_FAILED');
            case \Swift_Events_SendEvent::RESULT_SPOOLED:
                return $translator->trans('RESULT_SPOOLED');
            case \Swift_Events_SendEvent::RESULT_PENDING:
                return $translator->trans('RESULT_PENDING');
            case \Swift_Events_SendEvent::RESULT_TENTATIVE:
                return $translator->trans('RESULT_TENTATIVE');
            case -1:
                return $translator->trans('RESULT_DELETED');
        }

        return '';
    }