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.
At my work we have something in place that prevents somebody from sending to more than 50 recipients but we control our own mail servers and know how many people are in the largest department
Basically, things like this exist but aren’t necessarily intuitive to set up and defaults would require contextual knowledge