It's important to know which service to use when you need documentation for your important letter or parcel. The terms “Registered" and “Certified" are often used interchangeably but are actually for very different services.

Certified mail provides a mailing receipt, a trackable number and proof of receipt. It is often used for legal documents and other mail items requiring provable delivery by a specific date.

For a much higher cost and with strict packaging requirements, Registered mail provides the services of Certified mail, plus additional protection for items that are irreplaceable or have monetary value. Registered mail may currently be insured for up to $25,000. The Hope diamond was shipped to the Smithsonian institution via Registered mail in 1958 and was insured for $1 million.

Either service can be tracked using the item's tracking number. By adding a USPS return receipt (the PS Form 3811 “green card") to either a Certified or Registered mail piece, the sender will receive the card back in the mail after delivery, with a hand-written signature and date of delivery.​​