I think I've figured out how to stop receiving junk snail mail. Unlike Kramer's method to stop the intrusions into his mailbox by the Pottery Barn catalog, which required that he fill his mailbox with bricks, this method keeps the legitimate mail coming. In fact, you probably will still receive Pottery Barn catalogs, but I'm mostly concerned with stopping all of the newsprint advertisements that get shoved in my mailbox. I don't want the ads from Ralphs, Albertsons, Vons, Jons, Food4Less or Vallarta Supermarkets.
The trick is to leave the junk mail in the mailbox. Only take the real mail out. Then, when the postal worker comes to deliver more mail, there's not enough room for more junk. I've only been doing this for about a week, but it seems to work. The junk mail is folded vertically, and the real mail is also placed within the protective shield of junk. I simply remove the envelopes in the center and leave the undesirable outer crust. I'm thinking about stapling all the junk together to make for easy removal and reinsertion, and to prevent the possibility of real mail sneaking in between.
Updates: This passive-aggressive attempt to stop junk mail was unsuccessful, but you can join the fight to stop junk mail by refusing delivery of it. The struggle continues.
The state is that great fiction by which everyone tries to live at the expense of everyone else. - Frederic Bastiat