mailman help needed


I have spent the day trying to set up mailing lists on OSX 10.4.2.
I only want to use this to send employees messages therefore it will only be used locally. As far as I can see everything is set up correctly but when I send a mail to the list nothing happens. I looked at the Delivery Failures log and I get the following: "delivery to LISTNAME@SERVERNAME failed with code -1 (7, 'No address associated with nodename')"

Anyone know what this means and/or how to fix it??