nsswitch

Having an issue where a webapp, postfixadmin, running on our webserver 
machine, fails to lookup its own ip address when sending mail through 
its locally running postfix.  The problem results in an inability to 
send mail to our own mail accounts.  From outside the firewall, port 25 
maps to our mail server on 192.168.0.10, but from behind the firewall, 
on the webserver, .20, the lookup for our outside ip fails.

How would I setup nsswitch and etc/hosts so that the webserver machine 
knows to lookup from file, first, before checking dns listing?  Once I 
can tell it to lookup from file first, then I can map the outside ip to 
our internal mail server on .10

Make sense?

any ideas appreciated.

thx,
W