public function get_special_folders($forced = false)
    {
        // getting config might be expensive, store special folders in memory
        if (!isset($this->icache['special-folders'])) {
            $rcube = rcube::get_instance();
            $this->icache['special-folders'] = array();

            foreach (self::$folder_types as $type) {
                if ($folder = $rcube->config->get($type . '_mbox')) {
                    $this->icache['special-folders'][$type] = $folder;
                }
            }
        }

        return $this->icache['special-folders'];
    }