/** * 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); } }