code: public function onToggleVisibility($blnDisabled, DataContainer $dc)
  	{
  		if (!$dc->id)
  		{
  			return $blnDisabled;
  		}
  
  		$objUser = $this->Database->prepare("SELECT email FROM tl_member WHERE id=?")
  								  ->limit(1)
  								  ->execute($dc->id);
  
  		if ($objUser->numRows)
  		{
  			$this->Database->prepare("UPDATE tl_newsletter_recipients SET tstamp=?, active=? WHERE email=?")
  						   ->execute(time(), ($blnDisabled ? '' : '1'), $objUser->email);
  		}
  
  		return $blnDisabled;
  	}
docs: Synchronize the newsletter subscriptions if the visibility is toggled
  
  @param boolean       $blnDisabled
  @param DataContainer $dc
  
  @return boolean