WebClient请求失败,因为客户端被视为过时的浏览器

当我打开IE或Chrome并键入URL时,请求工作正常。

这是我的代码:

    string url = @"https://www.royalmail.com/track-your-item?trackNumber=" + track.TrackingNumber;
        WebClient client = new WebClient();
        client.Headers.Add("user-agent", "Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; Trident/6.0)");
        string content = client.DownloadString(url);

我尝试调用的URL示例: https://www.royalmail.com/track-your-item?trackNumber=FP065628015GB