filterpostie.php Not being called

I have put a filterpostie.php file within my theme however none of the functions are being called

here is the demo function i tried to test

add_filter(‘postie_post_pre’, ‘my_postie_post_pre’);

function my_postie_post_pre($email) {
//Do something
$email[‘headers’][‘subject’] .= ‘ processed by postie_post_pre’;
return $email;
}