Email acceptable form of response to C&D?

Mr. Urbanczyk, who answered your other question, is correct that you can either respond or you can ignore. Since this isn't something that you actually have to respond to, there isn't any required way or timeline for you to respond. At my current job, we receive letters every day where a response isn't required, but that demands a response within XX number of days anyway. It's just an artificial deadline. With that said, things would probably be easier for you going forward if you provide a response and prior to this artificial deadline. I can't guarantee that, but I think that's the case more often than not. Esepcially here whe you're largely trying to appease the potential plaintiff to prevent them from pulling you into what you think is going to be a frivolous lawsuit against you. And I think you hit the nail on the head with that you would want some record of your response. Personally, I would call and explain the situation and then follow it up with an e-mail that confirms that you called as well. A letter would work, too. You probably wouldn't need the record for anything, but it's better to have the response on hand just in case.