Hi Everyone, first post here! I'd like some help with that situation: I have a CentOS server running up (Let's say IP: 10.00.00.01) Which emulate a Windows 2003 Server which has 2 Network Adapter. Let's say the IP of the IIS SMTP Server is 10.00.00.02. Right now, on the 10.00.00.02 server that is a web application running that must send e-mail. The email are being created (they are found in c:\inetpub\mailroot\queue). I'm pretty sure that it's the firewall of the centos that are blocking the mail (iptables). After a lots of unsuccesful attempt on iptables i've decided to remove everything that is being related to smtp and port 25 / 110 and ask for help! Anyone encountered the same situation and can give me the basis of iptables to allow the mail to be sent? Thanks a lot!