Email Storm
en.wikipedia.org
en.wikipedia.org
What they didn't realize was that the email server was overloaded and that their message would be delivered several hours later together with dozen similar messages from the other people.
The next round of people then complained why these people are not stopping.
The ones I have setup are pretty easy to stop since we do some basic checking of the e-mails sent anyway (e.g. attachment too large).
The more important question is, why email systems don't have default rules to prevent such an email storm?
When emails go to tens of thousands of people, a system should probably only allow it with special credentials or at least ensure that it's a read-only mailing list.
Other measurements would be to detect growing email chains and block emails when the chain has reached some threshold.
I'd argue 1hr response is pretty slow for the NHS, since they require 24/7 support availability of even their vendors. I imagine they responded pretty quickly but nobody had a plan in place for situations like this and a large public sector organisation isn't a place conducive to one person taking charge and fixing the problem immediately.
[0] http://osxdaily.com/2014/09/23/leave-group-message-chat-ios/
A friend of mine was in a business meeting on the same day UND announced its new logo and his phone went crazy. The person he was meeting with asked if he should answer it and he said "no, its a lot of bitter, bitter people and UND has no taste.". He did get the contract though.