public function swiftSend(
        $from_name,
        $receivers,
        &$successfulRecipients,
        &$failedRecipients,
        $subject = '',
        $body = '',
        $content_type = 'text/html',
        $charset = 'UTF-8'
    ) {
    
        if ($this->isSingle()) {
            Swift::component()->send(
                $from_name,
                $receivers,
                $successfulRecipients,
                $failedRecipients,
                $subject,
                $body,
                $content_type,
                $charset
            );
        }
    }