Why do we put stamps in the top right hand corner of an envelope?
Some interesting variations on this theme are posted in this article.
Gp
Or a more prosaic answer would simply be … that’s where the automatic franking and postmark machines are set to mark the sending office codes.
And before the age of machines took over? You try going through a heap of rectangles o’ folded paper, each one with a different damn stamp position. Same principle why banks prefer all banknotes either face-up or face-down, and all the same way up, when presented to tellers, into machines, etc.
Interestingly, I talked yesterday with a friend who has collected “covers” all his life. He is a serious philatelic student but didn’t have a quick answer. We did agree that, if there was ever a postal regulation, it pre-dated the advent of the adhesive stamp in the US in 1847. We have covers going back 50 years before that, when the postage amount was hand-written or “stamped” and it is almost always in the general upper righthand corner. I would suggest that there may have been a regulation, perhaps based upon a British regulation prior the the advent of the US postal system.