Validator

I've follow a MSDN example as below (at the moment for check e-mail address only) but the validator not work!! Where is my error?



<!DOCTYPE html PUBLIC "-//W3C//Dtd XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/Dtd/xhtml1-transitional.dtd">
<%@ Page Language="c#" %>
<%@ Import Namespace="System.Text" %>
<%@ Import Namespace="System.Web.Mail" %>
<script runat="server">

protected void Page_Load(System.Object sender, System.EventArgs e)
{
  lblStatus.Text = "";
}
private void btnSend_Click(System.Object sender, System.EventArgs e)
{
  //Creates the message
  StringBuilder sb = new StringBuilder();
  MailMessage msg1 = new MailMessage();
 
  // ...