ارسال ایمیل در ASP.NET

با سلام و وقت بخیر.برای ارسال ایمیل از نرم افزار و ارتباط با Mailserver کد زیر رو نوشتم: مسول شبکه گفتن که باید برای تمام certification ها مقدار true برگرده منم کد زیر رو اضافه کردم

  ServicePointManager.ServerCertificateValidationCallback = delegate { return true; }; 

using System;
using System.Collections.Generic;
using System.Net.Mail;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Net;
using System.Security.Cryptography.X509Certificates;
using System.Net.Security;

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

    }




    protected void button1_Click(object sender, EventArgs e)
    {


        try
        {
            SmtpClient client = new SmtpClient();
            client.DeliveryMethod = SmtpDeliveryMethod.Network;
            client.EnableSsl = true;
            //client.Host = "mail.scu.ac.ir";
            client.Host = "192.168.168.20";
            client.Port = 465;
            client.Credentials = new System.Net.NetworkCredential("rms@scu.ac.ir", "****");
           
            client.DeliveryMethod = SmtpDeliveryMethod.Network;
            client.EnableSsl = true;
            ServicePointManager.ServerCertificateValidationCallback = delegate { return true; }; 
            MailMessage mail = new MailMessage();

            //Setting From , To and CC
            mail.From = new MailAddress("***@scu.ac.ir", "RMS");
            mail.To.Add(new MailAddress("***@scu.ac.ir"));
          

            ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };
           

            client.Send(mail);

            Response.Write("<script>alert('mail Send');</script>");
            Label4.Text = "mail Send";
        }

        catch (Exception ex)
        {
            //Response.Write("<script>alert(ex.ToString());</script>");
            Label4.Text = (ex.ToString());

        }


    }
}

اما هنوز خطا زیر رو برمیگردونه 

System.Net.Mail.SmtpException: Failure sending mail. ---> System.IO.IOException: Unable to read data from the transport connection: net_io_connectionclosed. at System.Net.Mail.SmtpReplyReaderFactory.ProcessRead(Byte[] buffer, Int32 offset, Int32 read, Boolean readLine) at System.Net.Mail.SmtpReplyReaderFactory.ReadLines(SmtpReplyReader caller, Boolean oneLine) at System.Net.Mail.SmtpReplyReaderFactory.ReadLine(SmtpReplyReader caller) at System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint) at System.Net.Mail.SmtpClient.GetConnection() at System.Net.Mail.SmtpClient.Send(MailMessage message)