trackFilter example

$sql = 'SELECT email FROM s_campaigns_mailaddresses WHERE id=?';
            $email = Shopware()->Db()->fetchOne($sql, [$mailaddressID]);
            $user = $this->getMailingUserByEmail($email);
            $template->assign('sUser', $user, true);
            $template->assign('sCampaignHash', $hash, true);
            $template->assign('sRecommendations', $this->getMailingSuggest($mailing['id'], $user['userID']), true);
        }

        $body = $template->fetch('newsletter/index/' . $mailing['template'], $template);

        if (!$this->Request()->getParam('id')) {
            $body = $this->trackFilter($body, $mailing['id']);
        }

        if (empty($mailing['plaintext'])) {
            $body = $template->fetch('newsletter/index/' . $mailing['template'], $template);
        } else {
            $body = $template->fetch('newsletter/alt/' . $mailing['template'], $template);
        }

        if (empty($mailing['plaintext'])) {
            if (!$this->Request()->getParam('id')) {
                $body = $this->trackFilter($body, $mailing['id']);
            }