I have been using Digest Viewer <http://www.macupdate.com/info.php/id/5820> to handle my list mail under OsX. Although it is supposed to be $15 shareware I was waiting for some updates but the author seems to have disappeared. So I have been using it unregistered and except for a few caveats it works for me. I launch DV so the icon is in the Dock. I then dbl click on the digest in Mail to open it in its own window, do an Apple A of the messages (select all), do an Apple C (copy to clipboard), and click on DV to make it active and do a shift/apple/o which in DV is "Open from Clipboard." DV parses the messages and sorts them by thread. The are a number of prefs but I have DV "group messages by subject (ie thread.) The only thing it fails to do is to indicate quoted material which is poor but my efforts to contact the author haven't been successful. Give it a try. YMMV