Volume is key.
Having worked for over nine years as a mail carrier, I had moments where I despised junk mail. The "circulars" that went one to a house were the worst. However, while millions whine and try to determine how to eliminate the bothersome nuisance of "junk mail," most miss the point.
The cost of operating the United States Postal Service is tied directly into volume of mail handled. The less mail you have moving through the system, the higher it will cost per piece. Bulk business mail, which is classified as third class mail, represents more than fifty percent of the mail volume. Because of it, the cost to the average person to mail a letter of greater personal importance is kept lower. If you were to eliminate the horrible blight of "junk mail" it would likely mean doubling the cost of the stamp on your heartfelt letter to Aunt Ellie.
The postal service expends great time and effort to court companies who want to send out mass mailings. They do so because a very large portion of their annual expenses are paid for by these mass mailers.
It never ceased to amuse me how often people would leave "junk mail" in their mailbox and write across the front of it "return to sender" and assorted nonsense like that. Third class mail is not returnable. It is sent at a reduced cost because, unless it carries an address correction request, it is flying on a one-way ticket. It is technically illegal for the mail carrier or the post office to throw away the profaned junk mail, but it ends up happening. It does not go back to the sender. It won't unless you put a stamp on it. The mail carrier is not even allowed to pick it up without a stamp. Yet, they do, because it just isn't worth arguing over, and then they toss it in the undeliverable bin.
So you've received some third class mail you don't want. So you somehow feel extremely bothered by the concept of throwing away an envelope. So you decide to expend hours of effort figuring out how to get revenge on the mailer of the "junk mail." Remember that it doesn't much matter. Just throw it away. You're making a federal case about something that in the end is saving you money, unless you never have any reason to mail something.
Just throw it away
And get on with your life
Yes, indeed, a terrible waste of trees and such. Thanks for reminding me.