Special Shoutout to authors of the below post for inspiration.
https://www.werockyourweb.com/how-export-cpanels-mailman-mailing-list/
Here is a nice oneliner to export a mailing list for a client lickety-split.
Replace the user and maillist_email variables in the beginning to match yours.
user="cpanelusername";maillist_email="[email protected]";LISTNAME=$(echo $maillist_email|sed -e 's/@/_/') ; /usr/local/cpanel/3rdparty/mailman/bin/list_members ${LISTNAME} > /home/$user/${LISTNAME}_subscribers.txt && chown ${user}:${user} /home/$user/${LISTNAME}_subscribers.txt