Why not just have an easy button that you can click saying Do Not Allow Reply All?
I know that there are some ways you can limit reply-all availability, like in the URL linked here. But there’s a note: If recipients open this email in other mail applications except Microsoft Outlook, such as opening on web page via web mailbox, they can reply all this email.
I’m semi-tech savvy but I’m no programmer. It feels like it should be easy to do, so either I’m totally wrong or email services are really missing out on a great thing they could do.
I’ve pointed out that this issue could arrise so many times to companies with the all staff email. Every time they push back on wanting to define limited senders, “we don’t think it’s an issue/no one would do that!” Until someone sends an inappropriate email to the whole company, then it’s suddenly IT’s fault.