just add this to your code.html

<!-- by using indexOf( ) u can customize the condition about what are the valid email add u accepted.
-->

<script language="JavaS cript">
<!--
function isValid() {
var email=document. form1.t1.value;
if (email.indexOf( ' ')==-1
&& 0<email.indexOf ('@')
&& email.indexOf(' @')+1 < email.length...