Ditto on the previous 2 posts, and also, change this:
mail($email_to,$subject,$feedback);
to this:
mail($email_to,$subject,$feedback) or die('Mail error: Mailer could not send message!');
This way, we know if the problem is ocurring before the message ever hits the internet (i.e. config problem) or if it's perhaps just not reaching the intended recipient (spam filters, et. al.)
A good way to test your host's mail() ability (recommended if we're to help debug this for you) would be to send a very simple message, i.e.
mail('insert_your@email.here', 'test', 'Mail test successful!') or die("Couldn't even send the message.. likely config problem");