Mailgun\Messages\MessageBuilder::setDkim PHP Method

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

 /**
  * Enable/disable DKIM signature on per-message basis.
  *
  * @param bool $enabled
  *
  * @return \Bogardo\Mailgun\Mail\Message
  */
 public function dkim($enabled)
 {
     $this->messageBuilder->setDkim($enabled);
     return $this;
 }