The addressee has 15 calendar days to pick up your registered mail with confirmation of receipt (in the Post Office or Post Point mentioned on the failed delivery notice). If the addressee does not pick up your mail within 15 calendar days, it will be sent back to you.
Certified Mail provides proof of mailing and a delivery record, primarily used for important documents where confirmation of receipt is necessary. It is less expensive and faster than Registered Mail but offers less security.