Create a ISPConfig server with mail MX support

() Follow official doc

() Make sure you have the right root email before you activate email so you dont spam the wrong inbox :
  echo "myhostname.com" > /etc/mailname
  /etc/init.d/postfix restart

Troubleshooting 

If you see error connect to [127.0.0.1]:10024: Connection refused

Do this :

This command should be enough..
# postconf -e 'content_filter = amavis:[127.0.0.1]:10024'

Reload/Restart postfix ..
# postfix reload

And check if amavis is running..
# netstat -tap | grep amavis
(you should see a LISTEN port..)