I have seen similar email "storm" a couple of times when I was working in HP. It was not the whole of the company but a large business group probably a tenth of the company. It would start with a mail send to a large email list. People would start replying to all asking to be removed from the list or saying that they are not the intended recipient of the mail. After that it would be the "Please dont reply to all" mails. And that will go on and on . I remember a particular one that went into over a 100 mails.

It is interesting how a large group of smart people end up doing this.