This is what the law says:
While most of the time, people can and do get away with not stamping mail, violating the law can lead to a stiff fine and/or the unstamped mail being returned to the sender with postage due.
Oddly enough, yesterday I actually witnessed someone putting unstamped mail in the bank of mailboxes near our house. I had my two dogs with me and they were freaking out because they always do when strangers are around. I was struggling to walk them and had just dodged a car that was driving along our dirt lane. I had almost reached the mailbox and some woman pulled up in a minivan. She had a little girl with her. The girl got out of the car and put stuff in one of the mailboxes. I waited patiently for her to finish, not knowing if she was picking up mail for someone. She got back in the minivan. I glanced at her mom, who seemed to think my dogs' barking and carrying on was hysterically funny.
So then mom and daughter drive down the road. I was hoping that was the last of them so I could pick up my mail and get home. But instead of going to the end of the road, mom and daughter turned around and came back toward me and the dogs. There are no sidewalks on our road because it's a private dirt and gravel lane. Consequently, I was juggling the mail and my dogs, who were still barking like crazy. Mom was still laughing and I heard her kid make some shitty remark out the window. Merry fucking Christmas to you, too.
When I got back to the house, I started thinking about people who think it's okay to leave unstamped mail in mailboxes. A quick search on the 'net led to comments by people who think this rule is akin to it not being legal to pull the tag off a mattress. Another outraged comment came from someone who just wanted to save a little money by doing the legwork himself. Someone else claimed that she had self-delivered mail because she didn't know a friend's address, but did know where her friend lived. She said, "This rule can't apply to every situation, can it?" It was as if she felt she should be excused from committing a crime because she had good intentions and didn't know any better.
Here's the thing. The postal service may suck, but it needs money to survive. Across the country, post offices are closing and services are being cut because there's not enough money for them. People are not using the mail as much as they used to because they can use email and the Internet to conduct business. Cheating the postal service out of revenue means that people will eventually lose their jobs because there won't be enough money to pay them or maintain the infrastructure. Contrary to popular belief, the postal service is not a government agency paid for by taxes. It's a business.
Frankly, I don't want people putting stuff in my mailbox. The offenders are almost always people who are soliciting for their religion or business, not friends. Besides, mail is a sensitive thing. Maybe a lot of it nowadays is junk, but the mail can often contain sensitive information. Folks, this is how peoples' identities can get stolen. You may not be trying to steal mail when you drop off your unstamped Christmas card or wedding invitation, but someone else who would open a mailbox that isn't theirs might be. I just read this morning that people who would stoop to identity theft aren't necessarily strangers; in fact, they often tend to be friends and family who have more access to your information And how can we tell the difference between someone with friendly intentions and someone who means to do harm? We can't selectively apply rules to those who are up to no good. The rules have to apply to everyone.
We also need this rule in place to prosecute people who leave unsavory things in mailboxes. How would you like it if one of your neighbors decided to show their disdain for you by leaving a nice big pile of dog crap in your mailbox? If we allow people to put stuff in mailboxes that hasn't been through the mail system, how would you be able to prosecute someone who did something nasty? I can see it now... it's okay to leave cards, car keys, gift cards, compact discs, etc. But it's not okay to leave a pile of shit or live snakes or something equally unpleasant? What if you happen to think poop isn't gross or enjoy keeping snakes as pets? Nah... it won't work.
So that's my little PSA about the mail. It may seem like it's trivial and stupid and a pointless law, but really, there are good reasons why the rule exists. So be a good citizen and stamp your letters. Your postal worker will thank you.