function validateEmail(email) {
   var reg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
   if(reg.test(email) == false || email=='joe@ask.com') {
      alert('Invalid Email Address');
      return false;
   }
}