I feel silly not knowing this since I own 5 buildings but the issue hasn't come up until now. So I bought a 4-family building a while back that had no lock on the main exterior door to the building. This is the door that opens to the foyer which is where the mailboxes are. A new tenant asked me to install a lock, so I did and distributed keys to all the tenants. But now I am thinking, how will the mailman get in? I have other buildings that are always locked from the outside and the mailman gets in there fine, but the locks were put on before I owned those buildings. Does the mailman have some master key or do I need to take a copy of the new key to the post office? Seems crazy that the mailman would have a key to each building. In this neighborhood his key ring would weigh 10 pounds as there are a lot of apartments!
Edit: I live in Ohio if that matters. USPS is federal but maybe some things vary by state...