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.
Primarily, certified letters are sent so that the sender knows for sure the letter has been delivered and someone(a real person) has accepted the mailpiece. If this isn't as important, they may just elect to send the mailpiece with a tracking number, so they know when it was delivered.
What Is The Delivery Time For Registered Mail? Delivery DistanceLocalInternational Delivery Time In Business Days 2 4 to 7