‘Mailed notice’ or ‘notice by mail’ means the giving by the engineer, clerk, or any deputy thereof, as determined by the governing body, of any designated written or printed notice addressed to the last known owner or owners of each tract being assessed or other designated person at the last known address of each by deposit, at least 20 days prior to the designated hearing or other time or event, in the United States mails, postage prepaid as first-class mail. The names and addresses of such property owners shall be obtained from the records of the county assessor or from such other source or sources as the clerk or the engineer deems reliable. Any list of such names and addresses appertaining to any improvement district may be revised from time to time, but such a list need not be revised more frequently than at 12-month intervals. Any mailing of any notice herein required shall be verified by the affidavit or certificate of the engineer, clerk, the deputy, or other person mailing the notice, which verification shall be retained in the records of the municipality at least until all assessments and bonds appertaining thereto have been paid in full, or any claim is barred by a statute of limitations. Such affidavit of mailing shall be prima facie evidence of the mailing of such notice in accordance with the requirements of this section.