This is a 32 bit install of Office 2016 from the Office 365 site.
It gererates:
Either there is no default mail client or the current mail client cannot fulfil the messaging request.
Please run outlook and set it as the default mail client.
If you choose to Run as Administrator you do not get the message.
Any user who uses the laptop gets this message.
Tried Online repair, uninstall, reinstall of Office 2016 and saw the delete registry key posting somewhere on the net.
Outlook will run but gives the nag screen message.
Much thanks,
-bob