/**
* Add an unsubscribe email to the List-Unsubscribe header if applicable
*
* @param Events\EmailSendEvent $event
*/
public function onEmailSend(Events\EmailSendEvent $event)
{
if ($unsubscribeEmail = $event->getHelper()->generateUnsubscribeEmail()) {
$headers = $event->getTextHeaders();
$existing = isset($headers['List-Unsubscribe']) ? $headers['List-Unsubscribe'] : '';
$unsubscribeEmail = "<mailto:{$unsubscribeEmail}>";
$updatedHeader = $existing ? $unsubscribeEmail . ", " . $existing : $unsubscribeEmail;
$event->addTextHeader('List-Unsubscribe', $updatedHeader);
}
}