Won’t send to a second recipient

I have a working form that emails submissions to me. I also want it to email the person filling the form. I have a working “[email]” shortcode for that. But when I put it in the To field along with admin email, separated by a comma, it doesn’t send the second email. And when I add “Cc: [email]” (without the quote marks) into Additional Headers, it tells me I have invalid syntax.