startTLS example

                    $this->smtp->hello($hello);
                    //Automatically enable TLS encryption if:                     //* it's not disabled                     //* we have openssl extension                     //* we are not already using SSL                     //* the server offers STARTTLS                     if ($this->SMTPAutoTLS && $sslext && 'ssl' !== $secure && $this->smtp->getServerExt('STARTTLS')) {
                        $tls = true;
                    }
                    if ($tls) {
                        if (!$this->smtp->startTLS()) {
                            $message = $this->getSmtpErrorMessage('connect_host');
                            throw new Exception($message);
                        }
                        //We must resend EHLO after TLS negotiation                         $this->smtp->hello($hello);
                    }
                    if (
                        $this->SMTPAuth && !$this->smtp->authenticate(
                            $this->Username,
                            $this->Password,
                            $this->AuthType,
                            

$this->capabilities = $this->parseCapabilities($response);

        /** @var SocketStream $stream */
        $stream = $this->getStream();
        // WARNING: !$stream->isTLS() is right, 100% sure :)         // if you think that the ! should be removed, read the code again         // if doing so "fixes" your issue then it probably means your SMTP server behaves incorrectly or is wrongly configured         if (!$stream->isTLS() && \defined('OPENSSL_VERSION_NUMBER') && \array_key_exists('STARTTLS', $this->capabilities)) {
            $this->executeCommand("STARTTLS\r\n", [220]);

            if (!$stream->startTLS()) {
                throw new TransportException('Unable to connect with STARTTLS.');
            }

            $response = $this->executeCommand(sprintf("EHLO %s\r\n", $this->getLocalDomain()), [250]);
            $this->capabilities = $this->parseCapabilities($response);
        }

        if (\array_key_exists('AUTH', $this->capabilities)) {
            $this->handleAuth($this->capabilities['AUTH']);
        }