Can you reuse a stamp from a mailed letter that did not get postmarked?

Sadly, no.

I was guessing that would be the answer, but I figured it was worth checking. For some reason, the stamps on the DadMail I receive seem to go unmarked by the post office an unusually high percentage of the time. I received a letter from him today with four forever stamps on it, all unmarked, which seemed like a waste. So I wondered… I don’t suppose I could scrape those off and slap them on another letter?

According to 18 U.S.C. § 1720, paragraph 3,

Whoever knowingly uses in payment of postage, any postage stamp, postal card, or stamped envelope, issued in pursuance of law, which has already been used for a like purpose—
Shall be fined under this title or imprisoned not more than one year, or both[.]

So it looks like the Post Office is way ahead of me on that one.

But now here’s another question. I am reasonably certain the letter my dad sent me was not nearly heavy enough to warrant four stamps. I’m pretty sure it could have gotten by on two. If I were to go to the trouble of weighing it and checking the requirements, and found two of them were in fact not needed, would it be a violation to use just those two? Tragically, I think even the unnecessary stamps are now forfeit, as “which has already been used for a like purpose” suggests yes, their use for the purpose of mailing — even if the use was not required — now makes them tainted.

And anyone else remember hearing about that old trick where you write the receiver’s address in the sender space, and the sender’s address in the receiver space, so that when you don’t attach any postage it gets “returned” to the intended recipient? I wouldn’t exactly recommend trying it, but it looks like that’s only punishable by a fine under 18 U.S.C. § 1725. Although I am sure there is a fraud statute lurking out there you could tag that under as well.