Gov. Code, § 15570.62

The department, whenever it deems it necessary to ensure voluntary compliance with the due dates prescribed by law for submission of any remittance, claim for credit or refund, document, return, or other information delivered to the department through the United States mail or through a bona fide commercial delivery service, may establish a uniform policy for the acceptance of the remittance, claim for credit or refund, document, return, or other information in cases where the cancellation mark stamped upon the envelope containing the remittance, claim for credit or refund, document, return, or other information shows a date after the date specified in law. This policy shall not be construed as an extension of the prescribed time limits for remitting payments, filing claims for refund or credit, submitting documents, returns, or other information.