namespace HelperLib

{

    public class Pop3Utility

    {

​

        public static bool IsValidAccount(string hostname, int port, string username, string password, string proxyIp, int proxyPort)

        {

            var client = new Pop3Client();

            var tcpClient = ProxyTcpClient(hostname, port, proxyIp, proxyPort, null, null);

            var sslStream = new SslStream(tcpClient.GetStream());

            sslStream.AuthenticateAsClient(hostname);

            client.Connect(tcpClient.GetStream());

            return true;

        }

​

        public static TcpClient ProxyTcpClient(string targetHost, int targetPort, string httpProxyHost, int httpProxyPort, string proxyUserName, string proxyPassword)

        {

            const BindingFlags Flags = BindingFlags.NonPublic | BindingFlags.Instance;

            Uri proxyUri = new UriBuilder

            {

                Scheme = Uri.UriSchemeHttp,

                Host = httpProxyHost,

                Port = httpProxyPort

            }.Uri;

            Uri targetUri = new UriBuilder

            {

                Scheme = Uri.UriSchemeHttp,

                Host = targetHost,

                Port = targetPort

            }.Uri;

​

            WebProxy webProxy = new WebProxy(proxyUri, true);

            webProxy.Credentials = new NetworkCredential(proxyUserName, proxyPassword);

            WebRequest request = WebRequest.Create(targetUri);

            request.Proxy = webProxy;

            request.Method = "CONNECT";

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            Stream responseStream = response.GetResponseStream();

            Type responseType = responseStream.GetType();

            PropertyInfo connectionProperty = responseType.GetProperty("Connection", Flags);

            var connection = connectionProperty.GetValue(responseStream, null);

            Type connectionType = connection.GetType();

            PropertyInfo networkStreamProperty = connectionType.GetProperty("NetworkStream", Flags);

            NetworkStream networkStream = (NetworkStream)networkStreamProperty.GetValue(connection, null);

            Type nsType = networkStream.GetType();

            PropertyInfo socketProperty = nsType.GetProperty("Socket", Flags);

            Socket socket = (Socket)socketProperty.GetValue(networkStream, null);

​

            return new TcpClient { Client = socket };

        }

​

    }

}