Use this code:
protected void Button1_Click(object sender, EventArgs e)
{
System.Net.Mail.MailMessage MailMessage1 = new System.Net.Mail.MailMessage();
MailMessage1.To.Add("YourMailAdress");
MailMessage1.From = new System.Net.Mail.MailAddress("YourMailAdress");
MailMessage1.Subject = "Mail Subject";
MailMessage1.Body = TextBox1.Text;
MailMessage1.IsBodyHtml = false;
System.Net.Mail.SmtpClient SmtpClient1 = new System.Net.Mail.SmtpClient();
SmtpClient1.Host = "smtp.gmail.com";
SmtpClient1.Port = 587;
SmtpClient1.Credentials = new System.Net.NetworkCredential("YourEmail", "Your Password");
SmtpClient1.EnableSsl = true;
try
{
SmtpClient1.Send(MailMessage1);
Response.Redirect("SendMailSuccess.aspx");
}
catch
{
Response.Redirect("SendMailFail.aspx");
}
}