The question may seem elementary. But I imagine the mail-sorting and delivering process is almost entirely automated. It’s machines checking the postage stamps on those hundreds of millions of pieces of mail daily, not people.
Stamps don’t seem all that sophisticated - just sticky paper with printing on them. So, does the system spit out incorrect stamps and insufficient postage? How?
Are these letters delivered, but the error discovered when a postal worker puts them in a P.O. box or prepares to deliever them to a house?
If I wrote ‘34’ on a Barney sticker, as it appears on legal stamps, would it get past their machinery?
(The USPS web site is full of boring stuff about trying to sell you their services. They don’t answer cool questions like this. :D)