Hi, I have a linux iptables fw with two interfaces: internal and external (nating the internal traffic) with a public ip. In the internal interface I have a ms exchange server that forward all the external mail to the firewall via smtp. - After setup the linux fw I had a cisco router nating the traffic to internet and everything went fine. It seems therefore that the exchange server works properly. - With the linux machine everything works fine unless the outgoing smtp.I can telnet the port 25 of the external server but something happen once the smtp protocol has begun. In fact I can see with a sniffer that the protocol stop when the external server send back DATA. In this moment the local exchange stop of sending and the timeout is reached. - I tested other smtp applications to send out messages and work fine with iptables. But what happens with exchange?: works with cisco but not with iptables!! It's crazy!!! Any ideas? Thank you for your help Antonio Hi.
