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.