H4 Stamping resulted in 221g. How to request emergency appointment?

My wife applied for H4 stamping by drop box and she got 221g form. She has to go for interview with a USCIS document. We want to apply for emergency appointment. As per the US travel docs guidelines, for scheduling emergency appointments, we have to first schedule normal appointment and then request emergency appointment. But if I try to schedule normal appointment, I am getting redirected to use drop box again. Can we directly send mail to Chennai consulate asking for emergency appointment? Can anyone please provide Chennai consulate email address?