public function rename_folder($folder, $new_name)
    {
        if (!strlen($new_name)) {
            return false;
        }

        if (!$this->check_connection()) {
            return false;
        }

        $delm = $this->get_hierarchy_delimiter();

        // get list of subscribed folders
        if ((strpos($folder, '%') === false) && (strpos($folder, '*') === false)) {
            $a_subscribed = $this->list_folders_subscribed('', $folder . $delm . '*');
            $subscribed   = $this->folder_exists($folder, true);
        }
        else {
            $a_subscribed = $this->list_folders_subscribed();
            $subscribed   = in_array($folder, $a_subscribed);
        }

        $result = $this->conn->renameFolder($folder, $new_name);

        if ($result) {
            // unsubscribe the old folder, subscribe the new one
            if ($subscribed) {
                $this->conn->unsubscribe($folder);
                $this->conn->subscribe($new_name);
            }

            // check if folder children are subscribed
            foreach ($a_subscribed as $c_subscribed) {
                if (strpos($c_subscribed, $folder.$delm) === 0) {
                    $this->conn->unsubscribe($c_subscribed);
                    $this->conn->subscribe(preg_replace('/^'.preg_quote($folder, '/').'/',
                        $new_name, $c_subscribed));

                    // clear cache
                    $this->clear_message_cache($c_subscribed);
                }
            }

            // clear cache
            $this->clear_message_cache($folder);
            $this->clear_cache('mailboxes', true);
        }

        return $result;
    }