California Code, Elections Code - ELEC § 3012

Whenever the elections official is required to mail a vote by mail voter's ballot to any elector and the address to which the ballot is to be mailed is a point outside the territorial limits of the United States, the elections official shall mail the vote by mail voter's ballot to the elector by airmail and, if under any law of the United States official election ballots may be mailed without the payment of postage, the elections official shall so mail them.