The post office will hold certified mail for up to 15 days.
After 15 days if the person didn't sign for and pick up the certified mail that was sent to them, the post office will then return the certified mail to the sender and the sender will not get their money back.
Sending certified mail does not guarantee that the certified mail will be delivered, it's just a way for the sender to track the certified mail and get confirmation on when it's been signed for and delivered.
The postal carry or post office will attempt to deliver the certified letter or certified mail and will leave a notice if the recipient of the certified mail is not available to sign for the certified mail.
After 15 days of holding the certified mail it will be sent back to the sender.
You can refuse certified mail if you want to refuse as there's no legal requirement to sign for or accept certified mail as it is not illegal to refuse certified mail.
Certified mail is just mail that has been sent to you with a signature required to receive it so that the sender of the certified mail can have proof that you got the mail they sent.
There's no legal requirement to accept certified mail or sign for it.
You can either let the post office or postal worker know that you're refusing the certified mail and they will return it to the sender.
Even if the certified mail is from a court, legal system, attorney, city etc you are never required by law to sign for the certified mail.