I have a machine running Ubuntu server 8.04 with all the services I configured running ok. I use webmin to do my configurations and also have a dyndns hostname for the server. I can send and receive emails with postfix on the server. I have a client machine which has Thunderbird setup to send and receive mail through the server. The problem is that, I can only relay emails from my dyndns hostname only. I cannot send other domain emails like gmail ( if I setup the from email in thunderbird as firstname.lastname@example.org it sends but not email@example.com) Someone told me this is because by default ubuntu server is not an open relay server. Is there a way I can allow certain domains to send emails through? Your help will be appreciated.