Работа с socks5

           HttpWebRequest request = (HttpWebRequest)WebRequest.Create("сайт");
           request.Proxy = new WebProxy(proxy.Trim());
            request.Method = "POST";
            request.UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.167 Safari/537.36";
            request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8";
            request.ContentType = "application/x-www-form-urlencoded";
            request.Headers["Accept-Encoding"] = "gzip, deflate, br";
            request.Headers["Accept-Language"] = "ru-RU,ru;q=0.9,en-US;q=0.8,en;q=0.7,en-GB;q=0.6,en-AU;q=0.5";
            request.Headers["Cookie"] = "куки";
            request.AllowAutoRedirect = false;
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls11;
          
                var param = "параметры";
                byte[] sentData = Encoding.UTF8.GetBytes(param);
                request.ContentLength = sentData.Length;
                Stream sendStream = request.GetRequestStream();
                sendStream.Write(sentData, 0, sentData.Length);
                sendStream.Close();
                WebResponse res = request.GetResponse();
                Stream ReceiveStream = res.GetResponseStream();
                StreamReader sr = new StreamReader(ReceiveStream, Encoding.UTF8);
                Char[] read = new Char[256];
                int count = sr.Read(read, 0, 256);
                string Out = String.Empty;
                while (count > 0)
                {
                    String str = new String(read, 0, count);
                    Out += str;
                    count = sr.Read(read, 0, 256);
                }
 
            if (Out.Length > 500)
            {
                MessageBox.Show("Не удачно");
            }
            else if (Out.Length < 200)
            {
                MessageBox.Show("Удачно");
            }

string headers;
using (WebResponse res = request.GetResponse())
{
    headers = res.Headers.ToString();
}

var enumerator = (IEnumerator<KeyValuePair<string,string>>)response.EnumerateHeaders();
while (enumerator.MoveNext())
{
    string header = enumerator.Current.Key;
    string value = enumerator.Current.Value;
    ...
}