Hi,
use this javascript
function checkEmail() {
var email = document.getElementById('txtEmail');
var emailFormat = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
if (!emailFormat.test(email.value)) {
alert('Invalid Email');
email.focus;
return false;
}
Good Luck