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HttpWebRequest myHttpWebRequest = (HttpWebRequest)HttpWebRequest.Create("https://meineURL.com/Script.php");
                myHttpWebRequest.Method = "POST";

                myHttpWebRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0";
                myHttpWebRequest.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
                myHttpWebRequest.ContentType = "application/x-www-form-urlencoded";

                NameValueCollection nv = HttpUtility.ParseQueryString(String.Empty);
                nv["value"] = this.textBox1.Text;
                byte[] data = Encoding.ASCII.GetBytes(nv.ToString());
                myHttpWebRequest.ContentLength = data.Length;

                Stream requestStream = myHttpWebRequest.GetRequestStream();
                requestStream.Write(data, 0, data.Length);
                requestStream.Close();

                HttpWebResponse myHttpWebResponse = (HttpWebResponse)myHttpWebRequest.GetResponse();
                Stream responseStream = myHttpWebResponse.GetResponseStream();
                StreamReader myStreamReader = new StreamReader(responseStream, Encoding.Default);

                string pageContent = myStreamReader.ReadToEnd();

                myStreamReader.Close();
                responseStream.Close();
                myHttpWebResponse.Close();

                MessageBox.Show(pageContent, "Page Content");					

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string URL = @"https://meineURL/Script.php";
            WebClient webClient = new WebClient();

            NameValueCollection formData = new NameValueCollection();
            formData["value"] = this.textBox1.Text;

            byte[] responseBytes = webClient.UploadValues(URL, "POST", formData);
            string responsefromserver = Encoding.UTF8.GetString(responseBytes);
            webClient.Dispose();
            MessageBox.Show(responsefromserver);