I agree using the preferred city name works just fine for USPS, though maybe not for UPS/Fedex.

What I want to know is: Why isn't this preferred city+state mapping dataset for zip codes publicly available from USPS? It would be like 40kb of data for the entire thing. Why is this not public domain from the US Government?

Edit: or is this what I'm looking for (the "Physical City", "Physical State" columns? https://postalpro.usps.com/ZIP_Locale_Detail

It's missing 00501 at least (which zippopotam has), and military zip codes (which zippopotam doesn't have). Military zip codes are included in this file: https://postalpro.usps.com/areadist_ZIP5

Also fun fact 88888 is for "Operation Santa" uspsoperationsanta.com, which zippopotam is missing, but appears in the areadist_ZIP5 file.