Symfony version(s) affected: 4.3.0-BETA1

Description
When sending email using a newsymfony/mailer component an event\Symfony\Component\Mailer\Event\MessageEvent us dispatched.
Mailer component has two subscribers for this event:
\Symfony\Component\Mailer\EventListener\MessageListener
\Symfony\Component\Mailer\EventListener\EnvelopeListener
but non of them are fired in case of an event.

Commandbin/console de:ev also doesn't shows these listeners.

How to reproduce

1. create one simple twig template for html part of email, for example:

# templates/email/hello.html.twig<p>Hi {{ email.to }}!</p>

2. create a console command and inject Mailer in constructor

private$mailer;publicfunction__construct(MailerInterface$mailer)    {$this->mailer =$mailer;parent::__construct();    }

3. put inexecute method something like:

$email =newTemplatedEmail();$email            ->from('no-reply@domain.com')            ->to('me@domain.com')            ->subject('Test email message')            ->htmlTemplate('email/hello.html.twig')            ;$this->mailer->send($email);

3. get an Exception

In HandleMessageMiddleware.php line 82:
A message must have a text and/or an HTML part.
In Email.php line 427:
A message must have a text and/or an HTML part.

This exception raised because\Symfony\Component\Mailer\EventListener\MessageListener was not fired.

Possible Solution
¯\_(ツ)_/¯

Additional context
symfony/messenger is installed with default configuration
symfony/swiftmailer-bundle is not installed