Thanks to everyone's help, mailman3 is up and running for me on two servers with three lists, and they all work as far as I can see. I'm sending out invitations to users tomorrow. Yayy. Up until today, I had been stuck using a plugin in Joomla, which was not the best solution. I'm tickled pink, and my users will be, too.
Now I'm just playing and tinkering a bit.
I'd like to delete all my archives that are more than a certain age, e.g. more than a week old. I can easily do that with a cron job, deleting old files in
/opt/mailman/mm/var/archives/prototype/testlist@example.com/*
which is, as far as I can see the only place archive emails live.
However... I was wondering if there was some mailman command or config variable that would accomplish this without using cron.
billo