function isEmail(aStr){
    var reEmail=/^[0-9a-zA-Z_\.-]+\@[0-9a-zA-Z_\.-]+\.[0-9a-zA-Z_\.-]+$/;
    if (!reEmail.test(aStr)) {
        return false;
    }
    return true;
}

function chkfrm(theForm) {
    if (theForm.email.value == "") {
        alert ("Please enter valid Email address.");
        theForm.email.focus();
        return false;
    }
    if (!isEmail(theForm.email.value)) {
        alert ("Please enter valid Email address.");
        theForm.email.focus();
        return false;
    }
    return true;
}