code: public static function findSentByPid($intPid, array $arrOptions=array())
  	{
  		$t = static::$strTable;
  		$arrColumns = array("$t.pid=?");
  
  		if (!static::isPreviewMode($arrOptions))
  		{
  			$arrColumns[] = "$t.sent=1";
  		}
  
  		if (!isset($arrOptions['order']))
  		{
  			$arrOptions['order'] = "$t.date DESC";
  		}
  
  		return static::findBy($arrColumns, $intPid, $arrOptions);
  	}
docs: Find sent newsletters by their parent ID
  
  @param integer $intPid     The newsletter channel ID
  @param array   $arrOptions An optional options array
  
  @return Collection|NewsletterModel[]|NewsletterModel|null A collection of models or null if there are no sent newsletters