Email Validation

I have this form with these validators
<tr>
            <td><span class = "Normal">Your Email Address:</span></td>
            <td>
            <asp:TextBox ID="emailText" runat="server"></asp:TextBox>
             <asp:RegularExpressionValidator ID="validEmail"
                 runat="server"
                 ControlToValidate="emailText"
                 ErrorMessage=" ...