Turn off Cached Exchange Mode in Outlook by following the steps below.
In Outlook, click File > Account Settings > Account Settings.
Click your Office 365 account, and then click Change.
Under Offline Settings, uncheck Use Cached Exchange Mode.
(If you're an Office 365 subscriber with semi-annual updates, under Offline Settings, uncheck Use Cached Exchange Mode to download email to an Outlook data file.
4. Exit and Restart Outlook.
For more information and additional instructions from Microsoft, click here.