I have added this lines under $unsublink in /classes/es-sendmail.php
// LIST-UNSUBSCRIBE HEADER
$headers .= "List-Id: Your List identification\n";
$headers .= "List-Unsubscribe: <" . $unsublink . ">, <mailto:your_mail@email.com?subject=Remove " . $subscriber[0]['es_email_mail'] . " from mailing>\n";
//
Worked fine.
