Locating individuals that don't have proper physical addresses can often prove difficult. Sometimes people search for an address and only come up with a PO Box (aka POB) address, or a postal mail box (aka private mail box or PMB). You typically can't rent a PO Box or PMB without showing photo ID and have an alternate mailing address associated with it. However, once you obtain the POB or PMB address if you move your physical address no one is usually the wiser.
Obtaining someone's residential address from a Private Mail Box or P.O. Box address is something that investigator assisted searches can help with. Investigators have access to information and resources unavailable to the general public (and for good reason).
A Private Mailbox is different from PO Box rented in a Post Office. A Private Mailbox typically has a valid street address of a Commercial Mail Receiving Agent, such as a UPS Store, Postal Annex, Mail Boxes Etc or other private mail box store fronts.