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I've been using Postfix for more than a year now, to distribute mail from cron jobs to my non-root mailbox so that I can keep up with things. I recently configured it to be able to send and receive to the outside world, also. However I'm unable to communicate directly with it from any of the 5 other machines on my LAN! Attempting to do so gets a message "Connection closed by foreign host" when attempting to log into the POP3 side to check for mail. Sending mail gets a connection but then gets "Host not found" for the addressee, which is probably indicating that my hosts file doesn't have the correct alias in it.
I've opened ports 25 and 110 to the outside world, in iptables, and the rules for my local interface on the server machine allow any and all traffic from/to the LAN interface. My nightly scan of open ports shows that postfix is listening on port 25, but nothing seems to be listening on port 110. My /etc/xinet.d directory has no entry for postfix, but I do run it as a standalone service round the clock.
I found the settings in /etc/postfix/master.cf to be somewhat less than adequately explained despite the extensive comments. Is there something I've missed there that's causing the server to refuse incoming requests to the POP3 side of the server?