Iptables, email forwarding

[bsherwood]

I have a redhat 7.2 firewall with a redhat 8.0 pop3 email server and they are not on a local network together.

I recently reset the Iptables rules on the firewalll(big mistake) and now email is no longer being sent to the mail server. So by my master reasoning I'm guessing there was a rule forwarding email that is now lost.

A couple of things I have tried that have not worked(though its possible I'm doing something wrong)

1. iptables -t nat -A PREROUTING -t nat -p tcp $FireWallIP --dport 25 -j DNAT -to $EmailIP:25

2. iptables -t nat -A PREROUTING -d $FireWallIP -p tcp --dport 25 -j DNAT --to-destination $EmailIP:25(also tried $EmailIP)

3. iptables -A PREROUTING -t nat -i eth0 -p tcp --dport 25 -j DNAT --to $EmailIP:25(als tried $EmailIP)

The fireWall does have 2 ipaddresses,(external, internal) while the Mail server only has an external one. I've only tried using the firewall's external ip address. I did try the internal once, but it cut off internet for everybody on the network(the firewall also acts as the default gateway for our windows machines) Any help appreciated.

Thanks

[adam7979]

First, do postrouting for your email server (i suppose your email server is configured to use the firewall as gateway):

iptables -t nat -A POSTROUTING -s $EmailIP -o eth0 -j MASQUERADE

#enable port forwarding
echo "1" > /proc/sys/net/ipv4/ip_forward

iptables -t nat -A PREROUTING -t nat -p tcp -d $FireWallIP --dport 25 -j DNAT --to $EmailIP:25

[bsherwood]

I'm not sure if the email server uses the firewall as a gateway. The firewall is used as a gateway to my LAN but the mail server is connected to the same hub that the firewall is and that our T1 line comes in on.

[puntmuts]

I'm not sure if the email server uses the firewall as a gateway. The firewall is used as a gateway to my LAN but the mail server is connected to the same hub that the firewall is and that our T1 line comes in on.

What does the command route tell ?