I'm very pleased to finally report that the problem I had with Sky e-mails displaying very slowly in Eudora is fixed!
With the great help of @jumper, whose patience with this has been extraordinary, the fix turned out to be very simple indeed.
All I needed to do was to add -
127.0.0.1 assets.sky.com
127.0.0.1 helpforum.sky.com
127.0.0.1 www.sky.com
to the HOSTS file, and the messages now open after just a second or two of delay, instead of the 20 seconds or so it was taking before, which is fine with me!
They look fine and aren't apparently missing any elements either.
Amazing how you can take so long looking at ever more complex possible fixes, and the answer actually turns out to be something so simple!
Of course the Marks and Spencer e-mails will still be a problem, but now I know how to fix it when I next get one!
Cheers, Dave.