The DU Lounge

If it's the last line of an address. The scanners and readers will easily determine it's the zip. A picture is taken of almost every piece of letter mail, and if the automated machines can't read it, the image is forwarded remotely to live agents working somewhere, who can provide more assistance. They would then input the needed info while the letter is still in the loop of the machine processing, and the next time it is scanned, that input would be applied to the barcode sprayed on the right lower portion of the envelope. The technology has come a long way. Of course the Post Office has a myriad of other issues that may affect deliver time, outside of an address, LOL.