According to this report on Associated Press:
The best email storm I've heard of though, is the one involving journalists who were accidentally sent a mass email from the Casey Journalism Center at the University of Maryland inviting them to their "Casey Medals" Awards.
Officials said the storm started when some diplomats used the 'reply all' function to respond to a blank e-mail sent recently to many people on the department's global address list.
Most demanded to be removed from the list while others used 'reply all' to tell their co-workers, in often less than diplomatic language, to stop responding to the entire group, the officials said.
Some then compounded the problem by trying to recall their initial replies, which generated another round of messages to the group, they said.
According to Editor and Publisher the email snafu caused some interesting effects:
The back-and-forth sparked a circle of never-ending responses that, in some cases, kept hundreds of e-mails filling electronic mailboxes over several hours on Tuesday and Wednesday morning. But, in an unexpected surprise, it also brought many journalists in touch with old colleagues, while forging a number of new industry connections through something of an online cocktail party.
"People started chit-chatting back and forth and inviting themselves to the awards," said Kim Platicha, editor and publisher of Parentwise Austin magazine in Austin, Texas. "It really evolved from there, it was hysterical. I have already started an e-mail conversation with a couple of folks."