header - Php Mailer problem - messages marked as spam -

A few days ago I upgraded Php Mailer and now some email providers my messages mark as spam. This is what I see in the headers of the marked messages:

X-SpamTest-Info: {TO: header missing}

This is from my php file.

$mail->From       = $sender;
$mail->FromName   = $sender_name;
$mail->Subject    = $subject;
$mail->Body       = $body;
$mail->AddAddress($recipient,$recipient_name);
$mail->AddReplyTo($replyto,"No-Reply");

Dont know how to add "to" header and can't understand how it's possible that "to" is missing but email arrives to the correct "to" address...