UNIX for Advanced & Expert Users

Hi All,
I am running an email server on a Linux machine. My goal is to set up in a way that I can use pop3 to retrieve mail from a Windows machine using Outlook. Now I can download the messages from the Linux email server, however I can not send out messages. I encounter this error:
Relaying denied.
I am trying to look for a configruation file that I can added supposely an IP address or some sort.
Does anyone have any tip further into the investigation I would be appreciated.
Thanks

i just asked a similar question , just search for my threads and its my last one before this. if your using postfix you can look in the main.cf and master.cf config files in your /etc/postfix/ directory, and look for a section that says 'mynetworks' or something like that, and add your ip address to that list. also see the postfix.org website, it is very helpful and has some sample (usable) configurations for a few different setups. if your using sendmail take a look at the sendmail website.