using System.Net.Mail;
using System.Net;

on button click()
{
string toaddress = "abc@xyz.com"; //write reciver mail address there
MailMessage mm = new MailMessage(TextBox2.Text, toaddress);
MailAddress copy = new MailAddress("avx@yts.com"); //write reciver mail address there
mm.CC.Add(copy);
mm.Subject = "some message: " + TextBox3.Text;
mm.Body = "Name:" + TextBox1.Text + "\r\n" + TextBox4.Text;
mm.IsBodyHtml = false;
SmtpClient smtp = new SmtpClient("server name");
smtp.Send(mm);
Label1.Text = "Thanks";
TextBox1.Text = "";
TextBox2.Text = "";
TextBox3.Text = "";
TextBox4.Text = "";
TextBox1.Focus();