New subject: Fedora core 1 sendmail problems

Sunday, 28 March 2004

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(a)gssnet.com&gt;
Reply-To: For users of Fedora Core releases <fedora-list(a)redhat.com&gt;
To: For users of Fedora Core releases <fedora-list(a)redhat.com&gt;
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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