Mich. Comp. Laws § 8.11: Statutes; definition: registered mail.

Sec. 1.

Wherever there is contained in the statutes of this state the term or terms, or direction for the use of, "registered mail" or "registered mail, return receipt requested," such term or terms shall be deemed to include the term or terms "certified mail" or "certified mail, return receipt requested," and in the case of certified mail the receipt of mailing shall be postmarked.