Someone must be available to sign for each USPS Certified letter. If you are mailing to a residential address and no one is home, a delivery reminder slip (Notice) is to be left in the mailbox by the letter carrier. This reminder informs the person that a USPS Certified Mail letter is being held at the local Post Office for pick-up. The recipient must go to the Post Office to sign for the letter and pick it up. After 15 business days, if the letter has not been picked up, it will be returned to the sender. However, a second delivery attempt within the 15 days can be scheduled by the sender. To learn more about scheduling a redelivery attempt, visit