Apparently there was a court case years ago where a U.S. attorney argued that the act of placing an envelope in a U.S.P.S. mailbox made you a presumed surety for the U.S. debt. The Post Office was replaced with the U.S.P.S. and doing business with them is now presumed to be a "privilege" or in any case contracting with a private corporation. However, unlike with U.S. Notes vs FRN's you have no reasonable alternative to the U.S.P.S. Thus you are "without recourse" and can note that on the envelope whenever you send something through the mail to void any presumed agreement to be surety for the U.S. debt. Not sure if I am actually presumed to be a surety just for placing an envelope in the mail, but I see no harm in adding the phrase "without recourse" to the "care of" address that I use. I also spell out the state name, and write "non-domestic, United States of America" in place of a zip code.