That's a serious issue also in my building of about 70 apartments, each one receiving some leaflets every day in the mailbox then throwing them away in a dedicated trashcan which has to be emptied at least twice a week. No way to complain with anyone since there's no postal service involved. During a residents meeting I suggested collecting all than junk for one year, then delivering it back in person to all businesses that spammed us, making it clear that they'd be going to be submerged by their trash, and apparently someone was considering that option. The problem is the huge waste of paper and materials, but the cost of printing and delivering by underpaid improvised irregular workers is so low that say only 2 people actually reading that junk might turn it into a deal for the spammers.