How should undeliverable unendorsed Standard Mail be handled?

Undeliverable unendorsed Standard Mail should be discarded in the Undeliverable Bulk Business Mail (UBBM) container because this method is specifically designated for handling such mail. When mail is unendorsed, it does not carry any instructions for forwarding or returning to the sender, making it necessary to dispose of it properly according to postal regulations. By utilizing the UBBM container, postal workers ensure that the mail is handled in compliance with established guidelines for undeliverable items, thus maintaining the integrity of the mail processing system and minimizing unnecessary delays in service.

The other handling methods indicated in the options do not align with the established protocols for undeliverable unendorsed mail. For instance, returning it to the sender or holding it for future delivery is not permissible without proper endorsements or instructions. Similarly, forwarding would require specific guidelines that unendorsed mail does not meet. Therefore, disposal in the UBBM container is the precise and correct procedure.