I had my subscription to haskell-cafe deleted because of intermittent bounces. I raised a support ticket with my ISP bluehost.com and they suggested the bounces might be because 78.46.100.80 is on the mxtoolbox blacklist as reported here: http://www.mxtoolbox.com/SuperTool.aspx?action=blacklist%3a78.46.100.180 HTH.