How to pass SIDF test.

QUESTION: How do I pass SIDF test?
The following is code that I use for reply email.
The code works great except that Hotmail reports the email as possibly unsafe because it does not pass the Sender ID Framework test.
Is there header information that I'm neglecting to send?
$from=$_SESSION["SendersEmail"];

$email=$_SESSION["RecipEmail"];

$subject="[MyAirParts.com] {$_SESSION["Subject"]}, Item#: {$_SESSION["ItemID"]}";
$message = wordwrap($values["Message"],70);
$headers = "From: <".$from.">";// . "\r\n";

mail($email, $subject, $message, $headers);