public static function instance($server = null, $email = null, $password = null)
 {
     if (is_null(self::$_instance)) {
         self::$_instance = new self($server, $email, $password);
     }
     return self::$_instance;
 }
function mdrop_connect_server()
{
    $user_id = get_current_user_id();
    $server = mdrop_get_server($user_id);
    $email = mdrop_get_email($user_id);
    $password = mdrop_get_password($user_id);
    return MDROP_Attachment_List::instance($server, $email, $password);
}