lib/Mailer.php
public function send(MessageInterface $message)
    {
        $response = $this->doSend($message);

        // We are all clear if status is HTTP 2xx OK
        if (in_array($response->getStatusCode(), range(200, 206), true)) {
            return;
        }

        $this->handle($response);
    }
public function send(MessageInterface $message)
    {
        $response = $this->doSend($message);

        // We are all clear if status is HTTP 2xx OK
        if (in_array($response->getStatusCode(), range(200, 206), true)) {
            return;
        }

        $this->handle($response);
    }
{@inheritdoc}