Based on what I have heard, using mailbox and messages is not hard, “all you do is put a text on a message to be sent (ex.open) and the mailbox that you have sent the messages to will then trigger (Mailbox/Out:destroyer)” but it does not work on mine for some reason. I may be missing something
You can play inside the editor to see if everything is running ok… like if the message is sent or is recevied and then you can find out whats missing.
If you can’t find it by yourself you can comment the game the link and one of us will help. 
Make sure the mailbox has matching text.