Hey folks, sorry I have to spam, but this is another trial to get this mailing list archived into publicly available mailing archives. It turned out that I had to remove a directive from the header of each e-mail "X-No-Archive: yes" (set by default with ezmlm) which restrained the publicly available mailing archives from archiving the e-mails on this list.
Hope it works now and I don't have to bother again with this kind of operative stuff. Thanks for your patience! Marco