string _email = "294243780@qq.com";
        Regex Rzz = new Regex(@"(.{2}).+(.{2}@.+)", RegexOptions.IgnoreCase | RegexOptions.Singleline | RegexOptions.IgnorePatternWhitespace);
        _email = Rzz.Replace(_email, "$1****$2", 1);
        Response.Write(_email);