protected function getPreviewFilePath(Swift_Mime_SimpleMessage $message)
    {
        $to = str_replace(['@', '.'], ['_at_', '_'], array_keys($message->getTo())[0]);

        $subject = $message->getSubject();

        return $this->previewPath.'/'.str_slug($message->getDate()->getTimestamp().'_'.$to.'_'.$subject, '_');
    }