public static function delete_dir($dir)
    {
        // This code can be executed from command line, make sure
        // we have permissions to delete keys directory
        if (!is_writable($dir)) {
            rcube::raise_error("Unable to delete $dir", false, true);
            return false;
        }

        if ($content = scandir($dir)) {
            foreach ($content as $filename) {
                if ($filename != '.' && $filename != '..') {
                    $filename = $dir . DIRECTORY_SEPARATOR . $filename;

                    if (is_dir($filename)) {
                        self::delete_dir($filename);
                    }
                    else {
                        unlink($filename);
                    }
                }
            }

            rmdir($dir);
        }

        return true;
    }