function checkEmail() {
  if(!document.getElementById('email').value.match(/^[\w\-\.\+]+\@[a-zA-Z0-9\.\-]+\.[a-zA-z0-9]{2,4}$/)) {
    alert('Please check your email address!');
    document.getElementById('email').focus();
    return false;
  } else {
    return true;
  }
}