We are adding more functionality to offline mode in the new Outlook for Windows. You will now be able to open and save attachments from your emails without an internet connection.   

Please note that this is only scoped to classic file attachments. OneDrive and SharePoint links in the body of the emails will still need a connection to be opened.   

For this functionality to work you need to make sure Offline is enabled and offline attachments are enabled.   

At the user level you can verify this by checking two settings in new Outlook Settings - General - Offline:   

1. Enable offline email, calendar and people  
2. Include file attachments  

This functionality will also be enabled or disabled based on the True/False behavior of the already existing Mailbox Policy: OWAMailboxPolicy- OfflineEnabledWin. 

Attachments from emails within the timeframe and folder scope selected in the "Settings - General - Offline" will be synced and available locally for users to open without an internet connection.  

This message is associated with Microsoft 365 Roadmap ID 472026