You can modify the beginning of AutumnBHs script to disable unwanted header injection.
Code:
if($_POST['posted'] == 'yes') {
$name = trim(preg_replace('/\s+/s', ' ', $_POST['name']));
$email = preg_replace('/[\s<>]+/s', '', $_POST['email']);
$subject = trim(preg_replace('/\s+/s', ' ', $_POST['subject']));
// etc