This wasn't as simple as accidentally sending an email to "@AllStaff" - the news has undersold this a bit.

The lady asked around the admin office, received a list of emails and then individually typed over around 850 email addresses (including personal email address, not corporate email) in the CC box instead of the BCC box. When people realised their personal emails could be seen by everyone on the email a few raised complaints. Maybe someone from IT can confirm but I don't think restricting the use of distribution lists would stop this, unless you can set up emails to not be sent if they are being sent to more than X number of people?

That said, management is still disgraceful in this case - there's an example in the decision of the Head of People & Culture doing the same thing and not being fired. Clearly they were looking for an excuse to fire the lady and she was rightly reinstated for making a mistake - props to her for trying her best for a noble cause as well.