So try to clear the offline items by following these steps: Resolution 2: Delete OST Files Outlook caches and stores email messages, calendar events and other items in Offline Storage Table (.ost) file.
The new contents such as emails, contacts, calendar items, tasks, notes and others are not updated and not downloaded even though user manually select “update folder” in order to pull the new data.
But user can login to OWA (Outlook Web Access) or to continue to access the missing email messages, appointments, contacts, tasks, journal entries, notes, posted items, and documents.
For more info about Hotfixes see; What are Hotfixes?
To obtain the Hotfix, you’ll need to request it via the link at the top of the KB article or use this direct link to the Hotfix request page instead.The fix should work directly after installing it; no additional configuring or resetting is required to make it work but you may need to restart your computer to complete the update process.Note: Unlike regular updates (which are being offered automatically via Windows Update), Hotfixes are basically pre-releases of updates that haven’t gone through all possible testing yet and are only meant to be installed to solve issues mentioned in the article.If you are not heavily affected by this issue, it is recommended to wait for the next public update or Service Pack which will also contain this fix.Resolution 1: Clear Offline Items Most Exchange account configured in Outloook has Cached Exchange Mode enabled by default to allow user to continue working with Outlook when offline in addition to improve the performance.
When the items in Outlook is mismatched with online version, the cached items may be corrupted.