Outlook Problem: Delegated Accounts with Sync or Performance Issues
In certain cases, delegated accounts can experience problems with performance and synchronization: items may be missing, deleted items may remain, overall performance may suffer.
This article applies to: Outlook for Mac, Outlook for Windows
If this happens, Microsoft recommends turning off caching of shared folders as documented on their Performance and Sync Problems support page. In the Resolution section of that page, follow the steps for Method 2: Disable caching of all shared folders.
We recommend that you enlist the aid of your local technical support staff.