Registered mail and certified mail are two distinct services offered by USPS. Registered mail is a service that provides the sender with a receipt acknowledging delivery or attempted delivery of mail; it also provides insurance coverage for the item. In contrast, certified mail provides proof of mailing and delivery, but does not include insurance coverage. Certified mail also requires the recipient to sign for the item when it is delivered.
When sending an item, the sender can choose to use either registered or certified mail—or neither—depending on their needs. If the sender wants to ensure that the item has been delivered to the correct address, they should use certified mail. If they want to ensure the contents of the envelope, they should use registered mail. Either service can be tracked online, but registered mail requires additional fees beyond the standard postage.