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Stevehe receipt I get from shipping something USPS without delivery confirmation/registered mail, etc. is just a receipt of paying for postage. It says nothing about whether the postage was actually used
It most certainly does.
It proves an item was sent because the receipt shows the zip code it was sent to.
The only receipt I get when I do not send a package is a receipt for stamps.
In this case the OP sent a parcel to the zip code.
Steve