Maybe you have not installed postgrey? On Debian and Ubuntu, you install it with: apt-get install postgrey and you can find its settings then under /etc
Hi Keagan, what's the mail log saying? When i started to install ISPConfig and had some issues the mail log was very good to troubleshoot the error. Please check the /var/log/ path for the log. I don't know the exact path because i'm not on debian / ubuntu.