S.D. Codified Laws § 58-8-10
Service of process in any such action, suit or proceeding shall in addition to the manner provided in §§ 58-8-8 and 58-8-9, be valid if served upon any person within this state who, in this state on behalf of such insurer, is:
and a copy of such process is sent within ten days thereafter by registered or certified mail by the plaintiff or plaintiff's attorney to the defendant at the last known principal place of business of the defendant, and the defendant's receipt, or the receipt issued by the post office with which the letter is registered or certified, showing the name of the sender of the letter and the name and address of the person to whom the letter is addressed, and the affidavit of the plaintiff or plaintiff's attorney showing a compliance herewith are filed with the clerk of the court in which such action is pending on or before the date the defendant is required to appear, or within such further time as the court may allow.
SDCL 58-8-10