A new OWAMailboxPolicy setting, AttachmentsOfflineEnabledWin, will roll out mid-April 2026, allowing admins to control offline access to file attachments in the new Outlook for Windows. It is enabled by default and works alongside the existing OfflineEnabledWin policy without affecting its configuration.
Applies to: Exchange Online · Microsoft 365 apps
Source: mc.merill.net — data via Merill Fernando's open archive (MIT).