Email: 
<asp:TextBox ID="TextBox1" Runat="server"></asp:TextBox>
  &nbsp;
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" 
  Runat="server" ControlToValidate="TextBox1" 
  Text="You must enter an email address" 
  ValidationExpression="\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*">
</asp:RegularExpressionValidator>
