mail sending asp.net c# script

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script

//Name Space:
using System.Web.Mail;

//Btn click:

MailMessage mail = new MailMessage();
mail.To = "user@gmail.com";
mail.From = "admin@admin.com";
mail.Subject = "Confirmation";
mail.Body = "Acoount confirmed....................";
SmtpMail.SmtpServer = "1:1:2:1";

try
{
  SmtpMail.Send(mail);
  Response.Write("Mail send successfully");
}
catch (Exception ex)
{
  Response.Write("sending failure:  "+ex.Message);
}

I wrote this code for sending mail in asp.net c# script. But an error has occured.
error is:

The transport failed to connect to the server

What is the reason for this error? I don't understand what is the correct problem of this error