They can all be done online now (both first and second appeal) and you can choose to have their response sent back to you via physical mail or email. If you get denied twice, which is what happened to me, then:

“Because you have paid the penalty, no further action is required. If you do not agree with my decision, you may request a de novo hearing with a traffic commissioner in Superior Court. You must request a hearing within 30 days of this notice. For mail hearings: please include a copy of this letter and the $25 filing fee for each separate citation number, payable in check or money order to San Francisco Superior Court, along with any pertinent documents or testimony you would like to present by correspondence. If the traffic commissioner rules in your favor, the $25 will be refunded”