I found this article too:
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Does it ever seem like junk mail is most of the stuff that comes through the letterbox? Stopping Junk Mail sometimes seems the hardest thing to do. Glossy brochures, special offers for things you don’t want, claims that you’ve won prizes from dodgy-looking companies you’ve never heard of? You’re not alone. More and more people want to stop junk mail. It wastes your time, produces unnecessary waste, and is frankly just plain annoying.
You may have read about stopping junk mail in the news lately, with reports of postman Roger Annies being suspended from his job for informing his customers how they could opt out of the junk mail he had to deliver on behalf of the Post Office. You may even have tried, already, to opt out of receiving junk mail yourself, but have found it a tricky process. You may have put up a “Stop Junk Mail” sign by your letterbox – and had it ignored.
First, let’s look at how you can stop junk mail by looking at how you get it in the first place.
There are two main types – junk mail that has been addressed to you (or to your house), and mail that has no address or name on it. Mail with addresses on has usually been sent to you because a company you have done business with has passed on your personal information to other companies, either for a payment or for some other reason. Often these other companies re-sell or otherwise share your personal information with still more companies! Junk mail with no addresses on is actually delivered by Royal Mail, in exchange for a payment from the companies sending it out.
What can you do about it? The first thing you can do for stopping junk mail is to “opt out” – a process that lets you tell the companies and organisations who send you junk mail that you don’t want any more.*****
I found it here: Articles on How to Stop Junk Mail Enjoy!