We use Office 365 and on friday we had a power shortage (dont know if this is relevant but better mention it)

Today when the user started outlook all email in outlook was missing except those from today.

In OWA it was the same, all mail exept todays is missing.

Finder locates all mail but the file extension is .olk14message.

When opening a file it shows that it is the correct message.

We tried the solution from this site (http://www.macworld.com/article/2029414/recovering-a-lost-outlook-message.html)

and after changing the file-extension to .eml the mail showed up in outlook.

But the mail is still missing in OWA.

The amount of mail missing is 1000+ so manually changing the file-extension is not a good solution.

My questions are:

Is there any way I can import these mail into outlook and get the synced to Office365 other than manually changing the file-extension?
Why did this happened?

How do we prevent it from happening again (have several MAC-users)