(Updated) Follow-up to MC1287370: Auto upgrade of shared calendars from legacy MAPI model to modern REST model

Updated June 2, 2026: We have updated the content and timeline. Thank you for your patience. 

This message is a follow‑up to MC1287370, which was recently sent as a broad communication.

Your organization will not be impacted by this change at this time, and you may safely disregard the earlier message. Your tenant is currently excluded from this rollout, and no action is required from you.

We are taking a progressive, phased approach to this change and are intentionally rolling it out gradually. Once this phase is complete, we expect to schedule this change for tenants like yours towards end of May (20th May)

This approach helps ensure that when the change reaches more complex or business‑critical environments, it is already well‑validated.

We will now begin rolling out this change in the middle of this week (June 2, 2026), representing a two-week extension from the originally planned date.

We have completed validation of this upgrade with an initial set of tenants and have not identified any issues. 

If you have any queries, please open a support request through standard Microsoft support channels.