Re: Fedora core 1 sendmail problems

Alexander has come to the conclusion, as I had, that the problem is not sendmail itself. He has been giving me substantial amounts of advice in email and has looked over some of my configs and thinks they are ok. During part of my debugging today, I decided to try procmail as well, and it suffers from the same problem. I can send mail, but not receive. I had tcpdump running all day, and could see Alexander trying to get to me. He would not get an immediate disconnect, but it seemed to timeout. During this time, my server was sending SYN,ACK pairs, but they apparently never got back to him.

The weird thing here, is that all web traffic works fine. Surely if there was a netmask problem of any sort, I would have the same problem - users would connect to one of my 4 or 5 virtual web servers running under apache, and not get anything back? All http traffic works fine, as do CGI script, Squirrelmail etc.

I'll try a few more ideas and post my findings when I get it working. It will be when, and not if!

Alexander deserves a public thanks for spending a LOT of time in emails with me trying to help resolve the problem, he gave me a lot of help, but as he said, remotely, it's very hard to diagnose a problem like this. Unfortnately, the weekend is almost over, and I have to go to work tomorro, so I'll try this again over the next few days.

From: Ron Herardian <rherardi@xxxxxxxxxx>
Reply-To: For users of Fedora Core releases <fedora-list@xxxxxxxxxx>
To: For users of Fedora Core releases <fedora-list@xxxxxxxxxx>
Subject: Re: Fedora core 1 sendmail problems
Date: Sun, 28 Mar 2004 19:03:17 -0800

In reviewing this thread it seems to me there could be an underlying network issue not related to the sendmail configuration, despite port forwarding for port 25 apparently working as before. Although the MTA is accepting connections from hosts on the local IP network (you can telnet to port 25 as Alexander reminded me) it may not be able to send a response to a host over the Internet.

As others have suggested, it's best to rule out network configuration problems, e.g., a wrong netmask or router setting that would not affect local traffic but that would break IP connections from remote networks. What you're observing might be produced, for example, if the route to the
remote network were incorrect, i.e., your server gets the TCP connect via port redirection through your NetGear box and sends an ACK but the remote never gets it because the ACK never leaves the local network (routing problem, e.g., bad netmask).

What happens when you try to telnet from a remote host (not on your local network)? If the connection is dropped right away it would suggest that the originating host cannot get a connection on port 25. If the connection times out, e.g., after a few seconds, it would suggest a firewall or routing issue, i.e., packets are lost or discarded/dropped. I suspect you'll find the latter.

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