From Longman Dictionary of Contemporary Englishcertified mailˌcertified ˈmail noun [uncountable] American EnglishTCM a way of sending post in which someone records that you have sent it, and the person it is sent to must sign their name to prove they have received it
Examples from the Corpus
certified mail• It also sent the memo by certified mail, with return receipt requested.• The Giants suggest sending the tickets by certified mail.From Longman Business Dictionarycertified mailˌcertified ˈmail American English a postal service which, for an additional payment, provides proof that a letter or package has been posted and deliveredSYNRECORDED DELIVERY BrEAll replies must be sent by certified mail. → mail 