I tweeted this link and mentioned "uptown" and @HackerNews. thank you for this link, upvote.
Of course, they have to detect your address with a computer.
But you can still drop a letter into a public mailbox, with no return address. Then only the recipient is tracked.
This will be a distant memory once the USPS declares that it's only going to accept eStamps from registered accounts. There will be a cross-platform app, though, so this change will be proclaimed by all media outlets to clearly be superior to all legacy solutions, and a sign of agile, efficient government.