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 use BCC semi-frequently at work because it prevents all kinds of (mostly unintentional) annoyances from my coworkers. Mostly with automated emails related to reports and/or our case management system. BCC is your best friend when used selectively.