Client Mail Server “” Up

     I was unable to determine the reason was returning an error code when trying to send.  There was no resource exhaustion I could identify, plenty of RAM, Disk, load was low, memory not exhausted.  Restarting postfix didn’t fix it and there didn’t appear anything bad in the queue.

     I opted for the Windows solution at this point and rebooted the server.  After the reboot it accepted and sent mail again.

     A post mortem analysis of the logs showed that the smtp daemon was unable to open /dev/null.  Not sure why it needs that but apparently something did go wrong in the operating system kernel. This is the first time I’ve ever seen a kernel issue on that version of Linux.