DV: the following javascript snippet may be of help dealing with spam to mailman-managed lists. It needs spamassasin to mark messages first, but it can be easily adjusted to look for different patterns in the header or in the body. The spam level that triggers automatic rejection can be adjusted as well: the current value works well enough for me.

javascript:for(i=0;i<document.forms[0].length;i++){
        if (document.forms[0][i].value=='3') {
                var name = "headers-" + document.forms[0][i].name;
                var headers = document.forms[0][name].value;
                if (headers.indexOf ("X-Spam-Level: ********") != -1) {
                        void(document.forms[0][i].checked=true)
                }
        }
}