Awesome idea, IF you are US only and don't cover edge cases and (want to depend on an external API or want to have some sort of eventually outdated map of city

Awesome idea, IF you are US only and don't cover edge cases and (want to depend on an external API or want to have some sort of eventually outdated map of city <> postcode). It is possible to do this properly, e. G., DHL and UPS do a somewhat okay job of it but isn't easy.