- Set your messenger preferences such that you can only get messages from people on your contacts list
- Message someone who is NOT on your list and ask them to reply
- They can't! They are blocked because of your privacy settings
This seems a bit ridiculous. You are not warned (that I've noticed) that the recipient will be blocked from replying. Equally well, I believe this should be a specific exception to the setting - if you message someone they should be able to reply.
I can see a few possible ways around this but as it stands it's not really satisfactory. You message someone and never get a reply and have no idea why.