protected function sendResponseMail( $recipientmails = '', $templateName, array $data = NULL, $type = self::MAILFORMAT_TXT, $subjectSuffix = '' )
    {
        $oldSpamProtectSetting = $GLOBALS['TSFE']->spamProtectEmailAddresses;
        // disable spamProtectEmailAddresses setting for e-mails
        $GLOBALS['TSFE']->spamProtectEmailAddresses = 0;

        $recipients = explode(',', $recipientmails);

        $from = [$this->settings['sendermail'] => $this->settings['sendername']];
        $subject = $this->settings['responseSubject'];

        // add suffix to subject if set
        if ($subjectSuffix != '') {
            $subject .= ' - ' . $subjectSuffix;
        }

        $mailHtml = '';
        $mailText = '';

        switch ($type) {
            case self::MAILFORMAT_TXT:
                $mailTextView = $this->getPlainRenderer($templateName, 'txt');
                break;
            case self::MAILFORMAT_HTML:
                $mailHtmlView = $this->getPlainRenderer($templateName, 'html');
                break;

            /** @noinspection PhpMissingBreakStatementInspection */
            case self::MAILFORMAT_TXTHTML:
                $mailHtmlView = $this->getPlainRenderer($templateName, 'html');
            default:
                $mailTextView = $this->getPlainRenderer($templateName, 'txt');
                break;
        }

        if (isset($mailTextView)) {
            $mailTextView->assignMultiple($data);
            $mailText = $mailTextView->render();
        }
        if (isset($mailHtmlView)) {
            $mailHtmlView->assignMultiple($data);
            $mailHtml = $mailHtmlView->render();
        }

        foreach ($recipients as $recipient) {
            $recipientMail = [trim($recipient)];
            $this->sendEmail(
                $recipientMail,
                $from,
                $subject,
                $mailHtml,
                $mailText
            );
        }

        // revert spamProtectSettings
        $GLOBALS['TSFE']->spamProtectEmailAddresses = $oldSpamProtectSetting;
    }