I'm sure if you check your postfix master.cf you'll find you only have it listening on localhost rather than it being anything "Outlook" specific.
Look for a line like this near the top of the file:
Code:
127.0.0.1:smtp inet n - n - - smtpd
Add another line the same but with the LAN IP address of your server instead of 127.0.0.1 or change the line to *:smtp and then restart postfix.