Welcome to WebmasterWorld Guest from 18.104.22.168
Open up a terminal window
sudo vi /etc/resolv.conf
add a couple of name servers
Save and exit.
Now try mailing again. I hope this saves someone a couple hours of frustration.
[edited by: coopster at 5:46 pm (utc) on June 7, 2008]
[edit reason] removed specific nameservers [/edit]