I understand your premise. Customer support through email is much like customer support in person. I spent six years doing in-person customer support while work

I understand your premise. Customer support through email is much like customer support in person. I spent six years doing in-person customer support while working through university. But email is a lot more than just a medium for handling customer support, I do hope you realize that. For instance, you can hire or fire a person over email, sign or terminate a contract, promote or demote, change organizational structure, among others. It's a powerful tool. Certainly when responding to clients, early is best, even if only to say "I'll look into it right away."