Problem with sending e-mails

I can send e-mails using usermin:20000 but how can I send e-mails from outlook or thunderbird? Which settings do I need to use to send messages? I don’t have problems with recieving e-mails.
I have default virtualmin installation on Ubuntu 8.04 and postfix.


You just have to tell it to authenticate when sending outgoing messages. I know Outlook doesn’t do that by default, but it’s just a matter of checking the checkbox within the Outlook preferences.