Couldn't work out what the problem was, so set up a new yahoo e-mail account & that worked. Compared all the settings and all except the obvious were the same.
The e-mail address was only used for yahoo group messages, so diverting them to the new address was not difficult. It seemed a way to get round the problem.
Windows 10 Home vs Windows 10 Pro comparison: Here are the extra features you get in the Pro version