Certified mail is a "signed-for" mail service that requires you to physically sign for an item in order to receive it. The U.S. Postal Service (USPS) assigns a unique tracking number to certified mail so the item is traceable at every stage of its journey. The tracking number doesn't identify the sender, however, and it's impossible to tell who sent the certified mail until you have the envelope in your hands.
USPS regulations require you to sign for certified mail before you receive and open it. You can't tell who sent it until you physically accept it.
There are several types of certified mail. The basic service provides a unique tracking number that the sender can check online to confirm that the item arrived at its destination. USPS requires a signature before the carrier hands over the item. Anyone at a business address can sign for the mail piece unless the sender has restricted delivery to an individual addressee. In the case of a residential delivery, if no one is home at the time of delivery, USPS leaves a delivery reminder slip in the mailbox and the addressee or an authorized agent must go to the local post office to sign for the item and pick it up. Businesses and lawyers often use certified mail because it gives them a clear paper trail and a legally recognized proof of delivery.
The USPS tracking code indicates where the item came from and the type of mail service the sender used. It does not identify the sender. This is deliberate; otherwise, you could refuse to accept a court summons, legal papers, notice from the landlord, a letter from a collection agency and other undesirable pieces of mail. You cannot hold, view or open the mail piece until you sign for it. It's impossible to know who sent you certified mail until you accept the letter.
Once the letter is in your hands, look at the return address. Certified mail requires the sender to write a return address on the mail piece, so you can see the sender's address before making a decision about whether to open the envelope. By this point, however, you have signed for the delivery. Even if you choose not to open it, you are deemed to have received it by a court of law. USPS maintains official delivery records for two years.
It's possible to refuse certified mail by not being present when the item is delivered, by refusing to sign for the letter, or by refusing to collect it from the local post office. If no one accepts the letter after three delivery attempts, USPS marks the letter "unclaimed" and returns it to the sender. Refusing certified mail still has consequences. If you're facing a complaint in the small claims court, for example, the other party may send a summons by certified mail. Upon your refusal of the item, the other party is able to show that he tried to contact you and serve the summons but you rejected it. You won't have notice of the court hearing, and the court may enter a judgment in your absence.