So it's Peachtree towers in MegaCity 1.

Judge Dredd approves.

China: Bulldozes Kowloon Walled City

Also China:

Mailroom aside, if a delivery guy is fine crossing a city with 20/30k people horizontally in traffic, I don't really see why this is such a bad thing when you break it down.

I count 35 floors, so you can cut it down to ~850 people on each floor after an elevator ride, and a building like this will probably have at least 4 elevator areas sectioning the building almost equally.

So you're down to about ~210 people after entering the right side of the building, that's like a big street / small neighborhood (and how far you have to walk should scale closely to that). And with this much people in one area you can really easily batch deliveries. And a delivery place will probably settle quite closely to such a hub of people anyways.

They probably have a number of diverse food kitchens in there, and would most likely "buy local", anyway. That building being basically a slum, I doubt that there is much delivery from the outside.

Luckily each unit has a number that indicates the floor and each floor probably has a floormap near the elevator, so you won't have to go knocking on random doors until you find the person.

Same thing for making deliveries in cities of several million. If there's an effective addressing system, it's usually trivial to find the destination, or at least to get very close to it and switch to "ok wtf is going on here with the last bit of this address?" mode.

where is the parking

Delivery guy was there.

One single letter box.

Just do what my delivery drivers do. Leave it at the main entrance and mark it delivered.