I wanted to migrate from Windows Live Mail 2012 to Outlook, using the Export command in Live Mail. It started, ran briefly, then crashed. I then discovered that all my emails in Live Mail had lost their content. The headers are there, but each one gives the following message:

"Message cannot be found

The contents of this message cannot be found."

I am running Windows 10 and Office 365 Personal. My message store is in a OneDrive folder. All copies of the message store were synchronized automatically before I discovered the problem.