public static MailFactory GetInstance()
 {
     if (_instance != null)
     {
         return(_instance);
     }
     lock (_locker)
     {
         if (_instance == null)
         {
             _instance = new MailFactory();
         }
     }
     return(_instance);
 }
        public static MailFactory GetInstance()
        {
            if (_instance == null)
            {
                lock (_locker)
                {
                    if (_instance == null)
                    {
                        _instance = new MailFactory();
                    }
                }
            }
            return _instance;

        }