Outlook 2007 on Windows 10 suddenly fails "no email program associated"

[AV-6807831]

I had been using Outlook from MS Office 2007 quite successfully on Windows 10 when, on trying to open it a while ago, it reported "The file OLMAPI32.dll is incompatible with MS Office Outlook. Install Outlook again."
I found advice online that this might be a problem associated with having multiple copies of Office on the PC, and indeed there is a trial version of Office 365 which has been there since I bought the PC. I therefore uninstalled Office 365, rebooted and tried Office 2007 again. Word, and Excel fired up fine, but Outlook now came up with the legend
"There is no program associated to perform the requested action. Please install an email program, or if there is one already installed, create an association in the Default Programs control panel."
I do not really understand what is being asked of me here.
Can someone please explain, and get me back in touch with my emails, please?