protected function _send($message)
    {
        $options = [
            'headers' => ['Authorization' => 'Bearer ' . $this->getConfig('api_key')]
        ];
        $response = $this->http->post('/api/mail.send.json', $message, $options);
        if ($response->getStatusCode() !== 200) {
            throw new SendgridEmailException(sprintf(
                'SendGrid error %s %s: %s',
                $response->getStatusCode(),
                $response->getReasonPhrase(),
                implode('; ', $response->json['errors'])
            ));
        }

        return $response->json;
    }