/var/mailman/bin/withlist -l -r fix_url <list_name> -u <new_hostname> -v

This trick comes in handy when your company’s gotten a new URL and you want the subscription confirmation messages and various other things to use the new URL. It also doesn’t hurt to poke around in /var/mailman/Mailman/mm_cfg.py and change a couple of things and restart the mailman process.