Opening your mailbox and seeing a flood of junk fall out has become so normal that we don't even notice it. Odds are there is a recycling bin next to your mail room and you unconsciously dump all the random junk you get into that bin.
Luckily, there are a few tricks that we can do to stop getting so much paper spam in our mailboxes.
Opt out of Credit Card Offers
The most well known site is https://www.optoutprescreen.com/ - an official site ran by the three major credit bureaus. Ironically enough, you have to verify your SSN and other information first, but after that's done they will allow you to unsubscribe from all mail for the next 5 years.
Note: I have heard about some people having problems using the site if their Social Security Number is too new. If that is the case, I am told you have to mail in your application instead.
Opt out of Catalogs and Magazine Offers
You can register for DMCA Choice for $2, and then uncheck all the categories of mail:
The blue envelopes full of coupons come from Valpak. Seeing as you can get the same offers right on their site, you can remove your mailing address from their system via this link: https://www.valpak.com/coupons/show/mailinglistsuppression
Unfortunately, it is impossible to opt out of those endless coupons stuffed into your mailbox. This is called Every Door Direct Mail, which is a service provided by USPS to raise additional funds. Local businesses can pay USPS to stuff their ads into your mailbox. As it is not addressed directly to you, there is nothing you can do about it.