@gulthaw @xssfox New Zealand has a lot like that - including mine. It's the postcode for one small office with a couple of thousand mailboxes in it. And - like at least 20% of NZ postcodes - it's a tiny enclave within another postcode.

The classic NZ postcode though is 9818. It covers the whole of the third largest island of NZ - and has absolutely no delivery points. Any mail to that island goes to (last I checked) the airport booking office (postcode 9846) until someone picks it up.