The mail spool NFS server is restored.

     The ethernet controller was wedged.  The kernel was stuck in a loop, resetting it and timing out.  Reboot cleared it without a power cycle suggesting it is software rather than hardware related.  There were many patches to the kernel to address meltdown and spectre, and it is a relatively new kernel, 4.15.0.  There was also a kernel patch waiting to be applied.  I have not yet managed to get live kernel patches configured so a reboot was necessary.