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.Port = 587;
            client.EnableSsl = true;
            object userState = msg;
            try
            {
                client.SendAsync(msg, userState);
            }
            catch (System.Net.Mail.SmtpException ex)
            {
            }
        }