In　this　paper,　we　investigate　how　to　combine　multiple　e-mail　filters　based　on　multivariate　statistical　analysis　for　providing　a　barrier　to　spam,　which　is　stronger　than　a　single　filter　alone.　Three　evaluation　criteria　are　suggested　for　cost-sensitive　filters,　and　their　rationality　is　discussed.　Furthermore,　a　principle　that　minimizes　the　error　cost　is　described　to　avoid　filtering　an　e-mail　of　＇Legitimate＇　into　＇Spam＇.　Comparing　with　other　major　methods,　the　experimental　results　show　that　our　method　of　combining　multiple　filters　has　preferable　performance　when　appropriate　running　parameters　are　adopted.　©　Springer-Verlag　Berlin　Heidelberg　2006.