Mailboxes are private boxes for mails of individuals from the post office. Yours truly and my DH have our own and I can see people living here in United States of America have their own mail boxes unless otherwise if the person is a homeless, or no contact to any person living in a house. When we say living in a house, it could either he/she rented it, already owned (no balances in the bank, not a loan anymore), or still paying the house from a loan. Rented apartment, condominiums, townhouses and alike considered already a house, a house rented that is. And I (with my DH) living in an apartment, yes rented apartment and we considered this as our abode. The mailboxes here is called cluster mailboxes, a vertical one. Each apartments have own and an own key (of course). An apartment complex is a commercial building hence the owner of this business have to purchase commercial mailboxes before the opening of this complex (which the owner purchased way back then) business. 

This cluster mailboxes comprised of Cluster Box Unit or CBU mailboxes to which as I said, one for every apartment. I have also seen horizontal apartment mailboxes near in the apartment complex we live or around the city. I can tell having an apartment rental, mailbox(es) is a must and a business owner should comply before operating. Yes community mailboxes, is really a must. Ooh yeah, that is one of the steps of operating a business like apartment rental and of course the mailboxes where a business would buy must be approved by USPS. Apartment complex by the way is a community of people living in an apartments.