N.D. Cent. Code § 32-19-27
Proof of service of notice before foreclosure may be made by the return of a sheriff or other officer, or by affidavit of the person making personal service or mailing such notice. Proof of death of the title owner of record may be made by a certified copy of the death certificate or by affidavit of any person having knowledge of the fact. Proof of any other fact necessary to show the notice was properly served, service was attempted and refused or unclaimed, or the property is abandoned may be made by certificate of a proper officer or of an abstracter or by affidavit of any person having knowledge of the facts. Such proofs together with the notice must be filed with the complaint in any action for the foreclosure of a mortgage and must be recorded with the notice and certificate of sale in foreclosures by advertisement.
N.D.C.C. § 32-19-27