How do I make custom mail notification events?

To create an event that shows up in the Mail Notifications part of the admin your event needs to extend Aero\Events\ManagedEventand have Aero\Events\ManagedHandleras a registered listener.
To create an event you need to create a class that extends Aero\Events\ManagedEvent.
<?php
namespace Acme\MyModule\Events;
use Aero\Events\ManagedEvent;
class MyEvent extends ManagedEvent
{
   //
}
To register Aero\Events\ManagedHandleras a listener of your event you need to add your event and the managed handler to a $listenarray inside of a service provider.
<?php
namespace Acme\MyModule;
use Acme\MyModule\Events\MyEvent;
use Aero\Common\Providers\ModuleServiceProvider;
use Aero\Events\ManagedHandler;
class ServiceProvider extends ModuleServiceProvider
{
   protected $listen = [
       MyEvent::class => [
           ManagedHandler::class,
       ],
   ];
   public function setup()
   {
       //
   }
}