First is a regular mail. It is for domestic first class or airmail. On the arrival at the destination of the mail, the addressee or a person at the address has to sign to get it. This is to ensure that it has got to the destination safety. If there is no one to receive it and sign, a notify is left to inform the addressee to collect it at the post office. Within one or two months if nobody shows up to collect it at the post office, the mail will then be sent back to the sender.