Jeff, thank you, it worked.
I took an old message [that was received and not forwarded or replied to]
that had this problem and replied to it. When sent, a copy now appeared in
the 'sent items' folder.
Suggestion: maybe it's me, but the instruction to uncheck has four elements,
so when reading it , you can 'feel' it's a good idea to check it, without
having really understood it. I still don't to be honest. I wonder if it could
be written more simply?
The relationship between the problem and solution is hard to understand.
Main thing is it's OK. Thanks again.