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I think he implied it but there are postal codes that refer to a single Mail Drop location.

For example, sometimes your tax return will have its own zip code in the USA.

Any mail addressed to members of ships' crews on vessels transiting the Detroit River can be delivered to them via J. W. Westcott II by being addressed "Vessel Name, Marine Post Office, Detroit, Michigan, 48222." (wikipedia)

At my university there were postcodes per large building

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