How to Disable Caching in Outlook for Shared Mailboxes

In Outlook 2013, 2016, 2019, and 2021 and Outlook 365 accounts, 

• Click File > Account Settings > Account Settings.
• Double-click on the email profile and click More Settings.

• Click the Advanced tab and then uncheck the Download shared folders option. 

• Click OK when the prompt to restart Outlook appears and then restart Outlook.

From now onwards, the mail items from Shared Folders won’t be synced or stored in the local cache, i.e., the OST file.