Looks like it's not a feature. Nod again to Thunderbird.
I upgraded my PC to Windows 10, and setup my roadrunner.com e-mail accounts in Mail. I now have Office 365, and want to export my accounts to Outlook 2016. A post on microsoft.com said to go to File >> Export. My problem is that there is no File menu, or any menus or other tool bars. Holding ALT doesn't do anything, nor does ALT-F or ALT-M. Right-clicking at the top blue area only shows only shows the typical Restore, Move, Size, Minimize, Maximize (all greyed out) and Close.