Outlook: open attachments while offline in the new Outlook for Windows

Updated August 27, 2025: We have updated the timeline. Thank you for your patience. 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:    Enable offline email, calendar and people   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 When this will happen: Targeted Release (Worldwide): We will begin rolling out on mid-May 2025 and expect to complete by late May 2025. General Availability (Worldwide): We will begin rolling out on late June 2025 and expect to complete by mid-August 2025. General Availability (GCC): We will begin rolling out on late August 2025 and expect to complete by mid-September 2025. How this will affect your organization: Classic 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: What you need to do to prepare: The default on or off of this feature will depend on your existing Offline configuration in the new Outlook via the following policy: OWAMailboxPolicy- OfflineEnabledWin.  This feature will not change the default of this Policy. You can find more information about this Policy here: Set-OwaMailboxPolicy   If you have not made any changes to this Policy, then the default of this feature will be on.