In 2016 the UK’s National Health Service (NHS) experienced an email storm that crashed their email system and resulted in snowball effect of 168 million emails being sent in a short period of time.
The cause? A new IT contractor for the company sent out a test email company-wide (the NHS employs 1.2 million people and 840 thousand of them received the test email). Many of them replied to it, wondering why they were receiving such an email using the “reply all” function and it snowballed from there into an email chain of epic proportions, an email storm.