Wow, I live in Queensland, Australia, and here if you put up a sign on your letterbox that says "Australia Post Only" or "No Junk Mail" or similar, your junk mail intake drops to basically zero immediately -- it's really effective. So effective actually that I've never had to lookup what actions to take if I still receive junk mail, because it just never happens. I looked it up just now and found this: https://www.ehp.qld.gov.au/waste/advertising-material.html