function valid_email(email) {
 var filter  = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
 if (filter.test(email)) {
  return true;
 } else {
  return false;
 }
}
function check_form() {
if (!document.contact_us.name.value) {
 alert('One or more mandatory fields are empty. All fields with a blue * are required.');
 return false;
}
if (!document.contact_us.email.value) {
 alert('One or more mandatory fields are empty. All fields with a blue * are required.');
 return false;
}
if (!document.contact_us.message.value) {
 alert('One or more mandatory fields are empty. All fields with a blue * are required.');
 return false;
}

}