Mailgun\Messages\MessageBuilder::setReplyToAddress PHP Method

    public function setReplyToAddress($address, $variables = null)
    {
        $this->addRecipient('h:reply-to', $address, $variables);
        return $this->message['h:reply-to'];
    }

 /**
  * Apply reply-to address from config.
  */
 protected function setConfigReplyTo()
 {
     $address = $this->config->get('mailgun.reply_to.address');
     $name = $this->config->get('mailgun.reply_to.name');
     if ($address) {
         $name = $name ? ['full_name' => $name] : null;
         $this->messageBuilder->setReplyToAddress($address, $name);
     }
 }