We had an MoD system brought to a shuddering halt because of a single email sent by one user. OK, she managed to somehow CtrlA, CtrlC, CtrlV the entire address book, including dist lists, into the To line and add a read and delivery receipt. The resultant cascade plus all the out of office responses that were de rigeur in those day froze the system to the point where we could not even talk to it. IIRC it took 2 days to effect a full recovery.