Using Windows Live Mail on Windows 10

For the last 4 years, I've been using Windows Live Mail on Windows 10 with no problems. Lately, items sent - received - deleted from today for example, reappear upon the next startup marked as unread. Would like to know how to fix.

I have spent several hours on the phone with a Microsoft Tech agent who was willing to go above & beyond for, as we're all well aware, Microsoft no longer supports Windows Live Mail. Unfortunately, although he thought the problem was repaired, it wasn't.  I prefer the setup to any other email program or app I've seen - - including gmail. 

Any help will be greatly appreciated - -