hello,

after all of my tutorial searching online i have'nt found any solution in my simple problem after all the trials of iptables command.

My problem is i have a centos box w/ 2 nics one is the modem ip and the other is for the lan, this acts as my firewall wanna be,

I want to test my friends e-mail server to be functional when passing through the firewall 1st to get out to the internet for its sending purposes.

It really does send mails to yahoo and others but when it replies back to my friends mail server nothing recieves.

is there any basic iptables command for this?

This doesn't initially sound like it has anything at all to do with iptables. You've not done a good job at all of explaining the layout there, but if you can reach smtp on other destinations it doesn't sound like it's a tcp level issue that iptables would be causing. Can you telnet to port 25 of this destination? You can show us your "iptables -vnL" output if you do think it's relevant.