In this paper we discuss the ease with which email can be used to breach confidence by the propagation of corporate secrets and intelligence, and propose an intelligent filtering system for outgoing emails aimed at preventing disclosures. We report on a number of experiments undertaken with a corpus of over half a million Enron emails and the use of a variety of techniques from the field of Corpus Linguistics for reducing the number of false alarms produced by na?ve keyword filtering systems, and discuss the results in detail. We also give due consideration to the danger of missing messages that should have been prevented from propagation.