protected function partIdIsChildOfAnAttachment($checkPartId)
    {
        foreach ($this->parts as $partId => $part) {
            if ($this->getPart('content-disposition', $part) == 'attachment') {
                if ($this->partIdIsChildOfPart($checkPartId, $partId)) {
                    return true;
                }
            }
        }
        return false;
    }