"Reply all" is the best single answer, but it also varies between lists -- on some lists, the norm is that you reply only to the list and don't CC the sender.

"Reply all" is the best single answer, but it also varies between lists -- on some lists, the norm is that you reply only to the list and don't CC the sender. For example this is the norm on many Debian mailing lists. Or at least some people firmly consider it a norm, and will grouch at people CC'ing them. The fact that this varies from list to list, and it's not encoded in software and you're just supposed to know which style to use, and that people then blame the human senders for not getting it right all the time, is among the reasons that mailing lists can be an unwelcoming medium.