I am not really sure about this, shall I really do that? What is the benefit for me, the owner of my family email domain But Apple already proved to be incorrect, so I guess I will just trust you in this.
Just to confirm is this the normal - dash character like on the US keyboard next to zero number, or some kind of special minus sign?
Normal minus sign. Itās a small change that allows you to decide what happens to the IPs not in the iCloud allowed list of senders. The tilde is a soft fail, meaning they fail, but are allowed through, the minus is a hard fail, so they donāt pass.
I have mine all set to the minus. Just remember that only iCloud is allowed to send emails, if you use any other service you need to add it there and allow it (as you should regardless).