parseCapabilities example

try {
                return parent::executeCommand(sprintf("HELO %s\r\n", $this->getLocalDomain()), [250]);
            } catch (TransportExceptionInterface $ex) {
                if (!$ex->getCode()) {
                    throw $e;
                }

                throw $ex;
            }
        }

        $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.');
            }