Cached Exchange Mode is a way to download email to your computer to be able to search through large archives faster and keep working even while you're offline. It can cause issues with shared and delegate mailboxes.
Disable Cached Exchange Mode
In Outlook, open the File menu.
Select the Account Settings menu and choose Account Settings...
You will see a list of emails. Choose the one that you want to turn cached exchange mode off for and select Change.
Un-check Use Cached Exchange Mode and select Next.
Select Done after the changes to the account have been confirmed.
Close the other dialog boxes that are still open and close and re-open Outlook for changes to take effect.