Final answer:
Undeliverable standard mail without an Ancillary Service Endorsement is treated as waste and disposed of by the USPS, as there are no handling instructions provided for these mail items.
Step-by-step explanation:
Undeliverable standard mail that lacks an Ancillary Service Endorsement is typically treated as waste by the United States Postal Service (USPS). This means it is not returned to the sender or forwarded. Instead, undeliverable mail without such an endorsement is disposed of by the USPS, as there are no instructions provided on how to handle the mail if delivery cannot be completed.
In contrast, adding Certified Mail service or an appropriate endorsement would provide specific handling instructions, such as return to sender or forwarding, and could allow for tracking, providing evidence of mailing and delivery.