Can your niece receive mail at your USPS PO box?

Yes, your niece can receive mail at your USPS PO box, provided she uses your PO box address as the mailing address. However, it's essential to ensure that her name is included on the mail or that you inform the post office about the arrangement to avoid any issues. You may also want to check with your local post office for any specific policies they may have regarding handling mail for non-registered users.