For the curious out there: the address and the zip code in a letter are not redundant. The former informs WHERE to go, the latter informs HOW to get there. Each digit of the zip code maps to a USPS sorting center that your letter will pass through.

And the 4 extra codes that no one uses in the US refers to the last mile delivery route to your house.

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Public utility information!

All i know is 90210.

Over here we can technically leave out city name and street name. They have become redundant by what we actually call "postal code". It is still good to have the redundancy though since many are handwritten and ocr still has issues in a lot of cases.

In my town, the full zip code uniquely identifies my PO box. (We don't have delivery to street addresses.)

Ireland?

West Virginia. Not even the very rural part!

No, because post codes in Ireland do identify street addresses.