Recipient Unavailable

If you are the sender of Certified Mail and no recipient is available when your letter is delivered, then the USPS postal worker will typically leave a notice for the recipient to pick the letter up at a specified post office location near to them.

Since the USPS is required to capture a signature for certified mail they can't simply leave the letter in the recipients' mailbox or at their door.

You can also attempt to schedule redelivery of your letter through the USPS website.