New Outlook for Windows will be available in GCC High and DoD environments starting Public Preview July 30, 2026, with general rollout from September to December 2026. It remains off by default and opt-in, allowing admins control via policies and registry keys. Migration from COM to web add-ins is recommended.
Applies to: Exchange Online
Source: mc.merill.net — data via Merill Fernando's open archive (MIT).