If a remittance to cover a payment required by law to be made to the state or to a state agency on or before a specified date is sent through the United States mail or through a bona fide commercial delivery service, as determined by the state or the state agency addressee, properly addressed with postage prepaid, it shall be deemed received on the date shown by the cancellation mark stamped upon the envelope containing the remittance or on the date it was mailed if proof satisfactory to the state or state agency establishes that the mailing occurred on an earlier date.
If a remittance to cover a payment required by law to be made to the state or to a state agency on or before a specified time on a specified date is sent through the United States mail or through a bona fide commercial delivery service, as determined by the state or the state agency addressee, properly addressed with postage prepaid, and the cancellation mark is placed on the envelope after it is deposited in the mail:
Ca. Gov. Code § 11002