IPN delivery failed. Unable to connect to the specified URL. Please verify the URL and try again.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Text;
using System.Net;
using System.Net.Mail;
using System.IO;
using System.Collections.Specialized;

public partial class IPNListener : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {


        string strSandbox = "https://www.sandbox.paypal.com/cgi-bin/webscr";
        string strLive = "https://www.paypal.com/cgi-bin/webscr";
        HttpWebRequest req = (HttpWebRequest)WebRequest.Create(strSandbox);
        //Set values for the request back
        req.Method = "POST";
        req.ContentType = "application/x-www-form-urlencoded";
        byte[] param = Request.BinaryRead(HttpContext.Current.Request.ContentLength);
        string strRequest = Encoding.ASCII.GetString(param);
        string strResponse_copy = strRequest;  //Save a copy of the initial info sent by PayPal
        strRequest += "&cmd=_notify-validate";
        req.ContentLength = strRequest.Length;

        //for proxy
        //WebProxy proxy = new WebProxy(new Uri("http://url:port#"));
        //req.Proxy = proxy;
        //Send the request to PayPal and get the response
        StreamWriter streamOut = new StreamWriter(req.GetRequestStream(), System.Text.Encoding.ASCII);
        streamOut.Write(strRequest);
        streamOut.Close();
        StreamReader streamIn = new StreamReader(req.GetResponse().GetResponseStream());
        string strResponse = streamIn.ReadToEnd();
        streamIn.Close();

        if (strResponse == "VERIFIED")
        {
            //check the payment_status is Completed
            //check that txn_id has not been previously processed
            //check that receiver_email is your Primary PayPal email
            //check that payment_amount/payment_currency are correct
            //process payment

            // pull the values passed on the initial message from PayPal

            NameValueCollection these_argies = HttpUtility.ParseQueryString(strResponse_copy);
            string user_email = these_argies["payer_email"];
            string pay_stat = these_argies["payment_status"];
            //.
            //.  more args as needed look at the list from paypal IPN doc
            //.


            if (pay_stat.Equals("Completed"))
            {
                SendEmail(user_email);
            }


            // more checks needed here specially your account number and related stuff
        }
        else if (strResponse == "INVALID")
        {
            //log for manual investigation
        }
        else
        {
            //log response/ipn data for manual investigation
        }
    }

    protected void SendEmail(string userEmail)
    {

        string MailFrom, MailTo, MailSub, MailMsg;


        MailFrom = "support@practicelifeintheuktest.co.uk";
        MailTo = "mmalik15@gmail.com";
        MailSub = "A user has made a payment";
        MailMsg = "Dear Support,<Br /><Br />" + userEmail.ToString() + " has made us a payment at " + DateTime.Now.ToShortDateString() + ". <br /> Thankyou.";

        DT_SendEmail obj = new DT_SendEmail(MailTo, MailFrom, MailSub, MailMsg);
        obj.SendEmailWithOutCC();

    }
}

Select allOpen in new window