Which of the following forms of mail requires the sender to have a confirmation of delivery?

Certified mail requires the sender to have a confirmation of delivery, making it the correct choice. This service provides proof that the letter was sent and allows for tracking until it reaches the recipient. Additionally, when the letter is delivered, the recipient must sign for it, which generates a delivery receipt. This evidence of delivery is important for legal and official correspondence where confirmation is necessary.

While other mailing options like Express mail also offer tracking and expedited delivery, they do not inherently require a signature for delivery confirmation as a standard practice. Priority mail functions similarly, providing faster delivery but lacking the same confirmation requirements unless specifically requested. Standard mail, on the other hand, is not designed for confirmation of delivery at all, focusing instead on cost-effective delivery without tracking or acknowledgment. Thus, certified mail stands out for its specific requirement for sender confirmation of delivery.