Legal Question in Civil Litigation in California

depends on what the parties' and/or counsel have agreed on.

Only if the answering and asking parties have agreed in writing to accept such service.

By my count this is at least the eighth question you have posted in the past few days about written discovery. If you need that much guidance, you should pay a lawyer to give it to you. This website is not designed to take the place of advice from a lawyer who knows your case.

There is no reason to email or fax responses. They are deemed served the day they are mailed.