Adding headers to email sent as a Laravel Notification

Question

Someone knows how to add headers to emails sent through Laravel Notification System?

I am not talking about Mailable classes where I can set header through the

Answer 1

Actually I've found 2 ways to append headers.

When the notification is sent via mail channel an Illuminate\Mail\Events\MessageSending event is fired.

Append a listener to it. In handle() you will get the Swift_Message object.

Or in the AppServiceProvider's register() method override the MailChannel with your own and append the header in the send() method.

$this->app->bind(
    \Illuminate\Notifications\Channels\MailChannel::class,
    MyMailChannel::class
);