问API调用在本地成功，但在网站发布后，即使在使用WebProxy之后也会失败。

EN

private async Task SendSmsUsingXML()
        {
            WebRequest req = null;
            WebResponse rsp = null;
            try
            {
                string fileName = Server.MapPath("~/App_Data/MultiTexterSMSFormat.xml");
                string uri = "https://www.multitexter.com/tools/xml/Sms.php";
                req = WebRequest.Create(uri);
                //req.Proxy = WebProxy.GetDefaultProxy(); // Enable if using proxy
                req.Method = "POST";        // Post method
                req.ContentType = "text/xml";     // content type
                //req.Proxy = new WebProxy("202.79.27.50", 8080);
                // Wrap the request stream with a text-based writer
                StreamWriter writer = new StreamWriter(req.GetRequestStream());
                // Write the XML text into the stream
                writer.WriteLine(this.GetTextFromXMLFile(fileName));
                writer.Close();
                // Send the data to the webserver
                rsp = req.GetResponse(); //I am getting error over here
                StreamReader sr = new StreamReader(rsp.GetResponseStream());
                string result = sr.ReadToEnd();
                sr.Close();
                Response.Write(result);

            }
            catch (WebException webEx)
            {
                Response.Write(webEx.Message.ToString());
                Response.Write(webEx.StackTrace.ToString());
            }
            catch (Exception ex)
            {
                Response.Write(ex.Message.ToString());
                Response.Write(ex.StackTrace.ToString());
            }
            finally
            {
                if (req != null) req.GetRequestStream().Close();
                if (rsp != null) rsp.GetResponseStream().Close();
            }
        }