Welcome Will to Tikiwiki community! ,
I've done my best to improve the documentation page
I suggest you to try
3. Under "Admin home > Login", you may want to modify these preferences:
- Checkbox "Users can opt-out internal messages:"
- Checkbox "Users accept internal messages by default:"
Can you try this, and if they solve your problem, can you improve documentation at doc.tw.o?
Or if you feel that this is a mistake and should be fixed, consider adding a bug report here:
Thanks, and welcome again ;-)