When you apply for a post office box (PO Box) at any United States post office, you must fill out USPS form ps1093. This form requires the disclosure of your physical address.
The USPS form ps1093 requires more disclosure than just the physical address of the PO Box applicant. It also requires information related to forms of personal identification that match the physical address.
Purpose of Disclosure
The United States Postal Service requires this information to provide a method of physical contact should a legal situation ever arise, as the details you provide confirm your identity and are traceable. The post office states at the bottom of ps1093 that the form details can be disclosed to USPS auditors and to law enforcement if needed as part of their duties.
The USPS publishes a "Privacy Act Statement" at the end of the form, stating that your information is never disclosed to third parties outside of the exceptions stipulated on the form. In some instances, a protective court order can be filed with the postmaster to prevent any form of disclosure without a separate court order being issued.