AcMailer\Service\Factory\MailServiceAbstractFactory::attachMailListeners PHP Method

    protected function attachMailListeners(MailListenerAwareInterface $service, ContainerInterface $container)
    {
        $listeners = $this->mailOptions->getMailListeners();
        foreach ($listeners as $listener) {
            // Try to fetch the listener from the ServiceManager or lazily create an instance
            if (is_string($listener) && $container->has($listener)) {
                $listener = $container->get($listener);
            } elseif (is_string($listener) && class_exists($listener)) {
                $listener = new $listener();
            }
            // At this point, the listener should be an instance of MailListenerInterface, otherwise it is invalid
            if (!$listener instanceof MailListenerInterface) {
                throw new InvalidArgumentException(sprintf('Provided listener of type "%s" is not valid. ' . 'Expected "string" or "AcMailer\\Listener\\MailListenerInterface"', is_object($listener) ? get_class($listener) : gettype($listener)));
            }
            $service->attachMailListener($listener);
        }
    }