Wherever notice is required to be given under a provision of Portland City Code, such notice may be given either by personal delivery thereof to the person to be notified or by disposition in the United States mail in a sealed envelope, postage prepaid, addressed to such person to be notified at the person’s last known business or residence address as the same appears in the public records pertaining to the matter to which such notice is directed. Service by mail will be deemed to have been completed at the time of disposition in the post office. Whenever a different method of serving notice is prescribed in Portland City Code for a specific purpose, all notices for such purpose must be given as prescribed in Portland City Code. Proof of giving any notice may be made by the certificate of any officer or employee of the City or by affidavit of any person over the age of 18 years that shows service in conformity with the provisions of Portland City Code or of any other law applicable to the subject matter concerned.