Exchange Web Services (EWS) deprecation starts October 1, 2026, affecting cross-tenant Free/Busy, MailTips, and Calendar Sharing. Migrate to Microsoft 365 Cross-Tenant Access Policy by September 2026 to avoid disruption. Rollout begins August 2026 worldwide; check tenant settings and follow migration guidance.
Applies to: Exchange Online
Source: mc.merill.net — data via Merill Fernando's open archive (MIT).