Email storm

An email storm (also called a Reply Allpocalypse) is a sudden spike of Reply All messages on an email distribution list, usually caused by a controversial or misdirected message. Such storms start when multiple members of the distribution list reply to the entire list at the same time in response to the instigating message. Other members soon respond, usually adding vitriol to the discussion, asking to be removed from the list, or pleading for the cessation of messages. If enough members reply to these unwanted messages this triggers a chain reaction of email messages. The sheer load of traffic generated by these storms can render the email servers inoperative, similar to a DDoS attack.

A related phenomenon occurs when a subscriber to a mailing list emails the mailing list to "UNSUBSCRIBE". People will reply to the hapless individual on the mailing list, half of them advising on how to unsubscribe, the other half referring to the manual of the mailing list manager. More subscribers will reply to the previous round of respondents, again to the list, this time about mailing list etiquette.

Some email viruses also have the capacity to create email storms, by sending copies of themselves to an infected user's contacts, including distribution lists, infecting the contacts in turn.

Examples

• On October 14, 1997, a Microsoft employee noticed that they were on an as-yet unknown email distribution list 'Bedlam DL3', and emailed the list asking to be removed. This list contained approximately a quarter of the company's employees, 13,000 email addresses. Other users replied to the list with similar requests and still others responded with pleas to stop replying to the list. A Microsoft employee estimates that 15 million emails were sent, using 195 GB of bandwidth.
• On October 3, 2007, an email storm was generated at the U.S. Department of Homeland Security, causing more than 2.2 million messages to be sent, and exposing the names of hundreds of security professionals.
• U.S. State Department employees were warned they could face disciplinary action for taking part in a massive email storm that "nearly knocked out one of the State Department's main electronic communications systems".
• In November 2012, New York University experienced a reply-all email storm due to an older listserv-based mailing list. There were 39,979 subscribed addresses affected.
• On 11 March 2013, over 8952 students from Imperial College London were subjected to an email storm after a final year medical requested to be removed from a mailing list, resulting in over 3.5 million email messages being sent. The mailing list was created, without permission, to advertise a campaign in the Imperial College Union Elections.
• On 18 March 2014, over 47 000 employees from Capgemini were subjected to an email storm after an email with a bad email list. The result was about 300 emails sent to this mailing list in 3 houres (reply all) which represents 14 millions emails (430 GB). Most of those emails were sent in order to signal a wrong recipient (or juste to indicate "+1"), to ask stopping doing "reply all", jokes, and explaination about how to create Outlook rules to immediatly put emails in the trash.

References

• How an e-mailstorm happens, University of Michigan
• Virus-induced email storms, University of Michigan

(Note: as of 0ct 23, 2013, both these links are broken)