Hi there,
after a fresh setup.
warning: hash:/var/lib/mailman/data/virtual-mailman is unavailable. open database /var/lib/mailman/data/virtual-mailman.db: No such file or directory
I'm not sure if i did it correctly but it works now.
touch /var/lib/mailman/data/virtual-mailman
postmap /var/lib/mailman/data/virtual-mailman
then restart postfix
kind regards