Cal. Rev. & Tax. Code § 6486
The board shall give to the retailer or person storing, using, or consuming tangible personal property written notice of its determination. The notice shall be placed in a sealed envelope, with postage paid, addressed to the retailer or person storing, using, or consuming tangible personal property at his or her 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, sub-post office, substation or mail chute or other facility regularly 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 it to the person to be served and service is complete at the time of 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 § 6486