@EventHandler
public void onMessagingPrestart(AepMessagingPrestartEvent event) {
  event.setFirstMessage(new MyFirstMessage.create()); 
}

public class SomeComponent {
  @EventHandler
  public void onMessagingPrestart(AepMessagingPrestartEvent event) {
    event.addInitialMessage(new Component1InitialMessage.create()); 
  }
 
  public void onFirstMessage(Component1InitialMessage message) {
    /*do something*/
  }
}

public class SomeOtherComponent {
  @EventHandler

  public void onMessagingPrestart(AepMessagingPrestartEvent event) {
    event.addInitialMessage(new Component2InitialMessage.create()); 
  }


  public void onFirstMessage(Component2InitialMessage message) {
    /*do something else*/
  }
}