eM Client when installed on Windows 10 Pro recognizes Windows 10 Mail as Thunderbird and consequently does not import any details from Mail.
Unfortunately, eM Client doesn’t allow direct import from Windows Mail client. You’ll have to either configure the accounts again in Menu > Tools > Accounts or export from Mail and import to eM Client.
Thanks Russel, Report I read must have confused Windows Mail with Windows Live Mail. eM Client imported Live Mail without any problems.