How do customers access their mail in a P.O. Box?

Customers access their mail in a P.O. Box using a key or combination that is provided to them upon renting the box. This access method is standard and ensures that only the individual who has rented the P.O. Box can retrieve their mail. The key or combination lock is specifically designed for security, preventing unauthorized access to the contents of the box.

Other methods like passwords or biometric scanners are not typically used for P.O. Box access, and while personal identification is important in various postal services, it does not pertain to the actual retrieval process at the box itself. Thus, the provision of a key or combination stands out as the established and secure means for customers to access their mail.