You get your postmark from the originating post office. If I drop something in the mail here, the local post office marks the item (verifying & invalidating the

You get your postmark from the originating post office. If I drop something in the mail here, the local post office marks the item (verifying & invalidating the postage), perhaps encodes the address in the barcode at the bottom (I don't recall whether that's centralized work or not), and sends it along its merry way to the destination. The postmark is obviously printed by a modern (impact?) printer. Why the post office would accept a mailing with incorrect postage for current times is notable - maybe someone making the call just shrugged it off an allowed it to pass.