certified mail
noun [ U ] US uk/ˌsɜː.tɪ.faɪd ˈmeɪl/ us/ˌsɝː.t̬ə.faɪd ˈmeɪl/ (UK recorded delivery)
（收件人签名的）记录式邮递，记录式投递
If a letter is sent by certified mail, the person who receives it must sign their name to show that it has been received.