code: public function setTransporter(TransportInterface $transporter)
      {
          if ($transporter->validate()) {
              $this->transporter = $transporter;
          } else {
              throw new \Exception(
                  sprintf('Transporter "%s" is not valid for current environment!', get_class($transporter))
              );
          }
          return $this;
      }
docs: Set a transporter
  
  @param \MimeMailer\TransportInterface $transporter
  @return self
  @throws \Exception if the default `transporter::validate()` does not return `true`