It's not clear to me even after reading MM archive posts how to contain this filesystem - /var/lib/mailman/archives/private.
So I go in and manually gzip the <listname>.mbox/<listname>.mbox file, but that doesn't stop the growth.
Yesterday I read about not gzipping the <listname>/2009-December.txt files so turned that off in mailman's cron.
104 lists on RedHat EL4 server.
Thank you for simple, clear ideas, I'm not a programmer nor much of a techie.