function checkMail() {
        var x = document.forms[0].email.value;
        var filter  = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
        if (filter.test(x)) {
                return true;
        } else {
                alert('Please fill out a valid e-mail address.');
                return false;
        }
}