addStamp example

return new Envelope($message, $stamps);
            }
        };

        $stamp = $this->createMock(StampInterface::class);

        $dispatcher = $this->createMock(EventDispatcherInterface::class);
        $dispatcher->expects($this->once())
            ->method('dispatch')
            ->with(self::callback(static function DMessageEvent $event) use ($stamp) {
                $event->addStamp($stamp);

                return 'Time for Symfony Mailer!' === $event->getMessage()->getSubject();
            }))
            ->willReturnArgument(0)
        ;

        $mailer = new Mailer(new NullTransport($dispatcher), $bus, $dispatcher);

        $email = (new Email())
            ->from('hello@example.com')
            ->to('you@example.com')
            

if (!$event->isQueued()) {
            return;
        }

        $message = $event->getMessage();
        if (!$message instanceof Message || !$message->getHeaders()->has('X-Bus-Transport')) {
            return;
        }

        $names = $message->getHeaders()->get('X-Bus-Transport')->getBody();
        $names = array_map('trim', explode(',', $names));
        $event->addStamp(new TransportNamesStamp($names));
        $message->getHeaders()->remove('X-Bus-Transport');
    }

    public static function getSubscribedEvents(): array
    {
        return [
            MessageEvent::class => 'onMessage',
        ];
    }
}