For a while now, every time i clicked a link inside any email , within the Windows 10 Mail app,
this failed with the warning 'Unable to open Link: http://... '.
After some research i've figured it is due to the fact that i stopped&disabled the windows Firewall service.
As soon as i opened services.msc , scrolled down to windows firewall, and started it - all windows 10 mail Links started opening up immediately, like magic!
Thanks Microsoft + Windows 10.
You're doing a great job.