In the US the post office will no longer deliver to "boxes" unless they are specified as boxes. At least that is the stated policy.

you used to be able to use 123 main st #100 or ste 100 but now supposedly you have to use box 100.

In most cities there are places that specialize providing peple or businesses with an actual address instead of a box #.

This is usually more expensive. For my US addresses I pay about $70.00 per month and that includes mail forwarding (plus postage). In Canada I just use regular boxes.

I travel a lot and have a few businesses so this is better than opening a place in each city.