Iowa Code § 321.505: Proof of service.

Proof of the filing of a copy of said original notice of suit with the director, and proof of the mailing or personal delivery of said notification to said nonresident shall be made by affidavit of the party doing said acts. All affidavits of service shall be endorsed upon or attached to the originals of the papers to which they relate. All proofs of service, including the restricted certified mail return receipt, shall be forthwith filed with the clerk of the district court.