code: public static function getTransport($domain, $key)
      {
          if (empty($domain) || empty($key)) {
              throw new InternalServerErrorException('Missing one or more configuration for MailGun service.');
          }
  
          return new MailgunTransport(new Client(), $key, $domain);
      }
docs: @param $domain
  @param $key
  
  @return \Illuminate\Mail\Transport\MailgunTransport
  @throws \DreamFactory\Core\Exceptions\InternalServerErrorException