Cal. Elec. Code § 3120

The elections official shall request an electronic mail address from each military or overseas voter who registers to vote. A military or overseas voter who provides an electronic mail address may request that his or her application for a ballot be considered a standing request for electronic delivery of a ballot for all elections conducted in the jurisdiction in which he or she is eligible to vote. An elections official shall provide for electronic delivery of a ballot to a military or overseas voter who makes a standing request for all elections conducted in the jurisdiction in which he or she is eligible to vote.