function isValidEmail(sEmailAddress) {
  var regexPattern = /[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}/i;

  if (sEmailAddress.match(regexPattern))
    return true;
  else
    return false;
}

function CustomEmailValidator(sender, args) {
  if (isValidEmail(args.Value))
    args.IsValid = true;
  else
    args.IsValid = false;
}

function isValidEmailAddress(emailAddress) {
  var pattern = new RegExp(/^(("[\w-\s]+")|([\w-]+(?:\.[\w-]+)*)|("[\w-\s]+")([\w-]+(?:\.[\w-]+)*))(@((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$)|(@\[?((25[0-5]\.|2[0-4][0-9]\.|1[0-9]{2}\.|[0-9]{1,2}\.))((25[0-5]|2[0-4][0-9]|1[0-9]{2}|[0-9]{1,2})\.){2}(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[0-9]{1,2})\]?$)/i);
  return pattern.test(emailAddress);
}