I am new to fedora. I have fedora 20 set up with postfix. It can send email, and receive mail sent from localhost. However, if I send it from within the local network, then the packets come in and are visible via tcpdump on port 25 but nothing is logged by postfix and the mail never arrives. I suspect a firewall issue, and added smtp as best I could. I do not suspect it is a problem with postfix but some other aspect of the operating system is not allowing the process to receive the mail from the network. How to troubleshoot?