RH9 Server + qmail

Hi Everyone,

I apologise if this is slightly OT, but my questions are both qmail
and linux networking related.

I have a ADSL modem/switch/router and a RH9 server setup as a DMZ.
I have a domain name example.com.au and a static ip that has been
setup correctly.
I have setup qmail for example.com.au

qmail is recieving mail and putting it into the queue, nothing is
being delivered to users however, the log says 'Sorry, i wasn't able
to establish an SMTP connection'. What is it trying to connect to, i
assume example.com.au:25?

I know that smtp is running on localhost.localdomain and on
example.com.au because i can telnet in.
I have disabled the firewall, and the users are legitimite. I have
tried to create an alias from localhost.localdomain to example.com.au.
This hasn't worked either!
Do i need to create a route entry so the program knows how to contact
example.com.au?
Also, what do i need for dns? The server is sitting behind the
modem/switch/router at address 192.168.1.1. Is this the only dns i
need or do i need to enter the dns of my isp? What is my dns search
path?

Should i make the hostname of my system 'example.com.au' or something
that is just specific to my lan?

I guess i am fishing for some advice here! Sorry about vagueness of
post, if there is anything else i can provide to help, let me know!

Thankyou all for any help, Andrew.