private void timer1_Tick(object sender, EventArgs e)
        {
                label1.Text = getIP();
        }

        private string getIP()
        {
            try
            {

                WebRequest myRequest = WebRequest.Create("http://network-tools.com");

                using (WebResponse res = myRequest.GetResponse())
                {
                    using (Stream s = res.GetResponseStream())
                    using (StreamReader sr = new StreamReader(s, Encoding.UTF8))
                    {
                        string html = sr.ReadToEnd();
                        Regex regex = new Regex(@"\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b");
                        string ipString = regex.Match(html).Value;
                        return ipString;
                    }
                }
            }
            catch (Exception ex)
            {
                return "Error";
            }
        }

namespace test4
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void timer1_Tick(object sender, EventArgs e)
        {

                label1.Text = getIP();

        }
      private string getIP()
        {
            try
            {

                WebRequest myRequest = WebRequest.Create("http://network-tools.com");

                using (WebResponse res = myRequest.GetResponse())
                {
                    using (Stream s = res.GetResponseStream())
                    using (StreamReader sr = new StreamReader(s, Encoding.UTF8))
                    {
                        string html = sr.ReadToEnd();
                        Regex regex = new Regex(@"\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b");
                        string ipString = regex.Match(html).Value;
                        return ipString;

                    }
                }
            }
            catch (Exception ex)
            {

            }
        }
}

       public void SendMail(String ip)
        {
            System.Net.Mail.MailMessage msg = new System.Net.Mail.MailMessage();
            msg.To.Add("you@yahoo.com");
            msg.From = new MailAddress("you@gmail.com", "IP Changed!!!", System.Text.Encoding.UTF8);
            msg.Subject = ip; 
            msg.SubjectEncoding = System.Text.Encoding.UTF8;
            msg.Body = "Your System ip changed to :"+ip +" at " +label4.Text ;
            msg.BodyEncoding = System.Text.Encoding.UTF8;
            msg.IsBodyHtml = false;
            msg.Priority = MailPriority.High;

            SmtpClient client = new SmtpClient();
            client.Credentials = new System.Net.NetworkCredential("you@gmail.com","password");
            client.Host = "smtp.gmail.com";
            client.EnableSsl = true;
            object userState = msg;
            try
            {
                client.SendAsync(msg, userState);
            }
            catch (System.Net.Mail.SmtpException ex)
            {
            }
        }