code: public function notifyOfReply(Contao\DataContainer $dc)
  	{
  		// Return if there is no active record (override all) or no reply or the notification has been sent already
  		if (!$dc->activeRecord || !$dc->activeRecord->addReply || $dc->activeRecord->notifyReply)
  		{
  			return;
  		}
  
  		$objNotify = Contao\CommentsNotifyModel::findActiveBySourceAndParent($dc->activeRecord->source, $dc->activeRecord->parent);
  
  		if ($objNotify !== null)
  		{
  			while ($objNotify->next())
  			{
  				// Prepare the URL
  				$strUrl = Contao\Idna::decode(Contao\Environment::get('base')) . $objNotify->url;
  
  				$objEmail = new Contao\Email();
  				$objEmail->from = $GLOBALS['TL_ADMIN_EMAIL'];
  				$objEmail->fromName = $GLOBALS['TL_ADMIN_NAME'];
  				$objEmail->subject = sprintf($GLOBALS['TL_LANG']['MSC']['com_notifyReplySubject'], Contao\Idna::decode(Contao\Environment::get('host')));
  				$objEmail->text = sprintf($GLOBALS['TL_LANG']['MSC']['com_notifyReplyMessage'], $objNotify->name, $strUrl . '#c' . $dc->id, $strUrl . '?token=' . $objNotify->tokenRemove);
  				$objEmail->sendTo($objNotify->email);
  			}
  		}
  
  		$this->Database->prepare("UPDATE tl_comments SET notifiedReply='1' WHERE id=?")->execute($dc->id);
  	}
docs: Notify subscribers of a reply
  
  @param Contao\DataContainer $dc