Here's my story: I am using Red Hat 9.0 for iptables to set up port forwarding so that we do not need to rely on another company for external email services. This will mean that we will only need the one email server that we have.

I was told that we could not use the firewall that we already have(that would be too easy) to set this up, and we have the DMZ that will be in between the External and the Internal address spaces. My Iptables firewall has a NIC on the External and one on the DMZ. The email server that I am using has a NIC in the DMZ and one on the inside. My current iptables set up is such that it already allows me to receive email, but not send it:

# Generated by iptables-save v1.2.7a on Thu Nov 4 12:16:26 2004
*mangle
:PREROUTING ACCEPT [1734:141563]
:INPUT ACCEPT [1732:141467]
:FORWARD ACCEPT [2:96]
:OUTPUT ACCEPT [1726:140991]
:POSTROUTING ACCEPT [1728:141087]
COMMIT
# Completed on Thu Nov 4 12:16:26 2004
# Generated by iptables-save v1.2.7a on Thu Nov 4 12:16:26 2004
*filter
:INPUT ACCEPT [1732:141467]
:FORWARD ACCEPT [2:96]
:OUTPUT ACCEPT [1726:140991]
COMMIT
# Completed on Thu Nov 4 12:16:26 2004
# Generated by iptables-save v1.2.7a on Thu Nov 4 12:16:26 2004
*nat
:OUTPUT ACCEPT [0:0]
:PREROUTING ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A PREROUTING -d 124.36.33.67 -i eth0 -j DNAT --to-destination 192.33.2.45
COMMIT


I have tried setting up a POSTROUTING and an OUTPUT chain to help with sending email, but that has not done me any good. I also checked my routes on the email server, and they appear alright. I am using WEBMIN to configure iptables, as I am pretty weak with it. Any advice with configuring IPTABLES to send email would be appreciated.

By the way, here is the iptable file that I have now, but while I can receive email, I cannot send it.

# Generated by iptables-save v1.2.7a on Thu Nov 4 12:16:26 2004
*mangle
:PREROUTING ACCEPT [1734:141563]
:INPUT ACCEPT [1732:141467]
:FORWARD ACCEPT [2:96]
:OUTPUT ACCEPT [1726:140991]
:POSTROUTING ACCEPT [1728:141087]
COMMIT
# Completed on Thu Nov 4 12:16:26 2004
# Generated by iptables-save v1.2.7a on Thu Nov 4 12:16:26 2004
*filter
:INPUT ACCEPT [1732:141467]
:FORWARD ACCEPT [2:96]
:OUTPUT ACCEPT [1726:140991]
COMMIT
# Completed on Thu Nov 4 12:16:26 2004
# Generated by iptables-save v1.2.7a on Thu Nov 4 12:16:26 2004
*nat
:OUTPUT ACCEPT [0:0]
:PREROUTING ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A PREROUTING -d 124.36.33.67 -i eth0 -j DNAT --to-destination 192.33.2.45
-A POSTROUTING -p tcp -m tcp -s 124.36.33.67 -o eth0 --sport 25 -j SNAT --to-s
ource 192.33.2.45
COMMIT


Again, thanks for any help.