... but not a problem I'll ever have. My email client simply doesn't have a 'reply all' feature, and was chosen with that very much in mind.
OK, so I'm not a business with thousands of clients, but even so, by now there should be a separate system in commercial products specifically for sending bulk messages where and when wanted.
P·S. I was going to say 'needed' but that's debatable anyway - needed by whom?