Protect partner calendar sharing
Microsoft's September 29 revision separates the rollout dates for replacing EWS-based cross-tenant sharing. Worldwide Free/Busy was scheduled to complete September 23, MailTips September 29 and Calendar Sharing October 15. GCC, GCC High and DoD rollouts are paused in the published tables. Administrators are told to wait until the feature reaches both their own and their partner's environments. This matters as gradual Exchange Online EWS disabling begins October 1: a replacement's announcement is not proof that every affected sharing function is ready.
Why it matters for leaders
Have the messaging lead inventory partner relationships and check Message Center before changing settings. Test availability, shared calendars and out-of-office information with a real partner. If continuity requires the documented extension, use a time-bounded, reviewed exception with a migration owner. Reserve support capacity for coordination across organizations.
Cost, service, risk & adoption
The Exchange team's revised guidance covers configured cross-organization Exchange Online sharing. It describes a temporary EWSEnabled=True continuity option through final EWS shutdown on April 1, 2027.
What the evidence cannot tell us
Dates are rollout guidance, not observed tenant state. Within-organization sharing and several hybrid/on-premises scenarios are outside this migration's scope.
Read the original sources
Summary and leadership analysis from the Week ending 2026-10-02 brief. The edition’s selection notes explain source access and evidence limitations.