public function folder_exists($folder, $subscription = false)
    {
        if ($folder == 'INBOX') {
            return true;
        }

        $key = $subscription ? 'subscribed' : 'existing';

        if (is_array($this->icache[$key]) && in_array($folder, $this->icache[$key])) {
            return true;
        }

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

        if ($subscription) {
            // It's possible we already called LIST command, check LIST data
            if (!empty($this->conn->data['LIST']) && !empty($this->conn->data['LIST'][$folder])
                && in_array_nocase('\\Subscribed', $this->conn->data['LIST'][$folder])
            ) {
                $a_folders = array($folder);
            }
            else {
                $a_folders = $this->conn->listSubscribed('', $folder);
            }
        }
        else {
            // It's possible we already called LIST command, check LIST data
            if (!empty($this->conn->data['LIST']) && isset($this->conn->data['LIST'][$folder])) {
                $a_folders = array($folder);
            }
            else {
                $a_folders = $this->conn->listMailboxes('', $folder);
            }
        }

        if (is_array($a_folders) && in_array($folder, $a_folders)) {
            $this->icache[$key][] = $folder;
            return true;
        }

        return false;
    }