Cal. Rev. & Tax. Code § 7671
The board shall give the supplier written notice of its determination. The notice shall be placed in a sealed envelope, with postage paid, addressed to the supplier at the supplier's address as it appears in the records of the board. The giving of notice shall be deemed complete at the time of the deposit of the notice in the United States Post Office, or a mailbox, subpost office, substation or mail chute or other facility maintained or provided by the United States Postal Service, without extension of time for any reason. In lieu of mailing, a notice may be served personally by delivering to the person to be served and service shall be deemed complete at the time of that delivery. Personal service to a corporation may be made by delivery of a notice to any person designated in the Code of Civil Procedure to be served for the corporation with summons and complaint in a civil action.
Ca. Rev. and Tax. Code § 7671