Cannot send a notification email

I'm trying to send a notification email as follows:

$post= Post::findOrFail($id);

$user = new User(['email' => '[email protected]']);

$user->notify(new ReportPost($post));

But this isn't working for some reason. No error, but I'm not receiving any email. But if I fetch a user from the database and try the same thing, it will work. Any idea?