The checkout form posts directly to the confirm page. The set session value server behavior on the checkout page will never trigger.
Move this code:
<?php
if (!session_id()) session_start();
if(isset($_POST["Checkout_x"])) {
$_SESSION["Email"] = "".((isset($_POST["email"]))?$_POST["email"]:"") ."";
}
?>
from the checkout page to the confirm page.