For anyone else wondering why isn't National Five-Digit ZIP Code and Post Office Directory in public domain like every other work of the US government:

>Works by certain independent agencies, corporations and federal subsidiaries may not be considered "government works" and may, therefore, be copyrightable. For instance, material produced by the United States Postal Service are typically subject to normal copyright.

https://en.wikipedia.org/wiki/Copyright_status_of_work_by_th...