Mailgun\Messages\MessageBuilder::setOpenTracking PHP Method

    public function setOpenTracking($enabled)
    {
        if (filter_var($enabled, FILTER_VALIDATE_BOOLEAN)) {
            $enabled = 'yes';
        } else {
            $enabled = 'no';
        }
        $this->message['o:tracking-opens'] = $enabled;
        return $this->message['o:tracking-opens'];
    }

 /**
  * Toggles opens-tracking on a per-message basis.
  * This setting has a higher priority than the domain-level setting.
  *
  * @param bool $enabled
  *
  * @return \Bogardo\Mailgun\Mail\Message
  */
 public function trackOpens($enabled)
 {
     $this->messageBuilder->setOpenTracking($enabled);
     return $this;
 }