[parent5446]

That's like saying if I send an email via Gmail, Google should feel free to do whatever it wants with the headers, because it's supposed to be publicly viewable so the mail server knows where it should go. (See also the NSA phone call metadata scandal.)

In reality, when you send a letter, you are placing it into the care of the postal service. Your letter is only handled by postal employees, and mailbox privacy is codified in federal law. There's clearly an expectation that the postal service is not releasing your information to third parties without your consent. The information on the outside of the envelope is not meant for, nor is it needed by, anyone other than the postal service

[jlarocco]

That's an interesting idea, but it's not true.

Nowhere does it say that post office employees are the only ones who can handle your mail, and in reality the postal service has a ton of contractors that also handle the mail. They do stuff like bulk delivery and OCRing hand written addresses.

A friend of mine contracted with one of the companies that does the hand writing recognition, and if the computers can't recognize an address then a picture of the envelopes get sent off to a team of data entry people who see the address on a screen and type it in by hand.

It's also fairly common for delivery people to screw up and deliver mail to the wrong address, especially in large apartment complexes.

There's also nothing special about postal employees. Why would you trust them more than anybody else? They're bound by the same federal mail tampering laws as everybody else, but nothing above and beyond that.

[gowld]

That's not true. Both your USPS envelopes and ISP/webservice headers are not protected by any law. The info can and is often shared with law enforcement based on simple request (without a warrant), if the 3rd party chooses to share -- which they often do. Sometimes Google and others have an official policy of resistance, but that's their choice, not your choice.