Apparently if one throws a brand new latest version office 365 Outlook programme on top of a brand new latest version windows 10 OEM on a brand spanking top of line solid state PC (or any other new PC for that matter) there is a sporting chance of Outlook showing a correctly set up POP3 address (send/receive test OK) but unable to actually send !!!!!!!!!!!
Go to command prompt (yes its back where it should be !) administrator and run sfc/scannow and it will normally cure the problem.
I really think Mr Gates should give us the money back !