protected function smtpSend($header, $body)
    {
        $bad_rcpt = [];
        if (!$this->smtpConnect($this->SMTPOptions)) {
            throw new Exception($this->lang('smtp_connect_failed'), self::STOP_CRITICAL);
        }
        //Sender already validated in preSend()
        if ('' == $this->Sender) {
            $smtp_from = $this->From;
        } else {
            $smtp_from = $this->Sender;
        }
        if (!$this->smtp->mail($smtp_from)) {
            $this->setError($this->lang('from_failed') . $smtp_from . ' : ' . implode(',', $this->smtp->getError()));
            throw new Exception($this->ErrorInfo, self::STOP_CRITICAL);
        }

        $callbacks = [];
        // Attempt to send to all recipients
        foreach ([$this->to, $this->cc, $this->bcc] as $togroup) {
            foreach ($togroup as $to) {
                if (!$this->smtp->recipient($to[0])) {
                    $error = $this->smtp->getError();
                    $bad_rcpt[] = ['to' => $to[0], 'error' => $error['detail']];
                    $isSent = false;
                } else {
                    $isSent = true;
                }

                $callbacks[] = ['issent'=>$isSent, 'to'=>$to[0]];
            }
        }

        // Only send the DATA command if we have viable recipients
        if ((count($this->all_recipients) > count($bad_rcpt)) and !$this->smtp->data($header . $body)) {
            throw new Exception($this->lang('data_not_accepted'), self::STOP_CRITICAL);
        }

        $smtp_transaction_id = $this->smtp->getLastTransactionID();

        if ($this->SMTPKeepAlive) {
            $this->smtp->reset();
        } else {
            $this->smtp->quit();
            $this->smtp->close();
        }

        foreach ($callbacks as $cb) {
            $this->doCallback(
                $cb['issent'],
                [$cb['to']],
                [],
                [],
                $this->Subject,
                $body,
                $this->From,
                ['smtp_transaction_id' => $smtp_transaction_id]
            );
        }

        //Create error message for any bad addresses
        if (count($bad_rcpt) > 0) {
            $errstr = '';
            foreach ($bad_rcpt as $bad) {
                $errstr .= $bad['to'] . ': ' . $bad['error'];
            }
            throw new Exception(
                $this->lang('recipients_failed') . $errstr,
                self::STOP_CONTINUE
            );
        }

        return true;
    }