• lists.example.com is the list email domain used as an example here
• list@lists.example.com is the example list used here

On the machine with mailman run

newlist <listname>

You will be asked for an email and password (don't use a secure password as it will be emailed to you in plain text).

Now you can manage the list at lists.example.com

rmlist -a <listname>

try running

sudo exim -d+route -bt list@lists.example.com

also check '/var/lib/mailman/data/virtual-mailman' contains 'list@lists.example.com'.