Legal Question in Family Law in California

That depends on whether there has been a final adjudication of the issues in the case, and the motion is for a modification, versus when there is an active pending case and the motion is for a change to or a new temporary order.

If the court already has jurisdiction over the other party, meaning they have been served and have filed a response, then motions can be served by mail on the party at the address they have listed on their response papers. If the court does not have jurisdiction, you would have to use an Order to Show Cause, and it would have to be personally served.