Port 25 rejected some times
I have a home automation device that when certain events happen it send emails to me. It was configured to go to my ISP, but because it only logs the email could not be delivered, no details, I changed it to go to my Centos 5.4 system so I could monitor the network with wireshark.
Most of the time the home automation device connects on port 25 with no problems. I did notice the home automation device always uses port 10000 for its port number on every connection, wireshark highlighted that.
I changed /etc/sysconfig/iptables to log when a connection from only the home automation device got to the end, but before the packet is rejected. The log entry shows the home automation device is trying to connect to port 25, but it does not indicate why it got to that point. There is a entry to goto ACCEPT for port 25. I was told by the manufacture of the home automation device, it makes a connection for each and every email it sends. So I though maybe it was trying to make multiple connections at the same time, and that was the reason the connection failed.
Maybe sendmail does not allow this?
But I can not find any configuration parameter in sendmail to control this.
The wireshark network trace file does not indicate this either, it shows the previous connection being closed and then another connection request being made. The failure does not always happen just after a connection is closed, most of the time the new connection is minutes later.
There are no other messages logged on /var/log/messages or /var/log/maillog or any other log file I can find when he problem happens.
I hope someone has some idea what is happening to cause this problem. I did not include all the configuration files or log files at this time because I did not know exactly which one will be the most helpful. I can provide them and any other information, just let me know what.