Microsoft is auto-upgrading shared calendars in Outlook and Exchange Online from the legacy MAPI model to a modern REST model, improving sync reliability and performance. The seamless, server-side rollout begins August 2026 for GCC High/DoD tenants, requires no user action, preserves permissions, and excludes events older than one year.
Applies to: Microsoft 365 suite
Source: mc.merill.net — data via Merill Fernando's open archive (MIT).