Charles Kenyon Junk mail is unsolicited commercial mail in which we have no interest. My junk mail may be your prize. Generally, though, we each get far more junk than we do prizes.
Papers are a major source of clutter.
That includes good offers, catalogs, free recipes, and sweepstakes entries. Each time you fill out one of those drawing entries at a commercial place, you are giving your name to at least one more mailing list. That list may be sold to many others. The second place your junk mail comes from is your registration of warranties, software, etc. Those registrations almost always have a box to check asking that your name not be given out or used for promotional mailings.