Ben Paypal IPN benim önceki $_SESSION['cart'] almak istiyorum

Paypal IPN Code I use. Everything working fine and script got the $_POST verileri bir örnek.

if (strcmp ($res, "VERIFIED") == 0) {
        $subject = time();
        $to      = 'my@email.com';
        foreach ($_POST as $key => $value) { 
        $body .= "\n$key: $value";
        }
        mail($to, $subject, $body); 
}

Question

if (strcmp ($res, "VERIFIED") == 0) {
 // 1. How to get my previous $_SESSION['cart'] here? 
 // 2. When I call my $_SESSION['cart'] here not ouput will come & it's empty.
 // 3. Or this code only to get $_POST data from Paypal website only?
}