Sending Email through ASP.Net Error

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ASM

Dear Friends

Using asp.net application i am trying to send email but receive the error message.please rectify it

Failure sending mail.

my code is as follows:-

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

namespace Letter
{
public partial class WebForm1 : System.Web.UI.Page
{


protected void btnSendmail_Click(object sender, EventArgs e)
{
// System.Web.Mail.SmtpMail.SmtpServer is obsolete in 2.0
// System.Net.Mail.SmtpClient is the alternate class for this in 2.0
SmtpClient smtpClient = new SmtpClient();
MailMessage message = new MailMessage();

try
{
MailAddress fromAddress = new MailAddress(txtEmail.Text, txtName.Text);
smtpClient.Host = "localhost";
smtpClient.Port = 25;
message.From = fromAddress;
message.To.Add("theadminking@gmail.com");
message.Subject = "Feedback";
message.IsBodyHtml = false;
message.Body = txtMessage.Text;
smtpClient.Send(message);
lblStatus.Text = "Message have been sent successfully";
}

catch (Exception ex)
{
lblStatus.Text = "Send Email Failed.
" + ex.Message;
}


}
}
}