On-premises users may see inconsistent results when viewing the hybrid free/busy information for Exchange Online users

Title: On-premises users may see inconsistent results when viewing the hybrid free/busy information for Exchange Online users User impact: On-premises users saw inconsistent results when they viewed the hybrid free/busy information for Exchange Online users. More info: While this issue was ongoing, users could have adjusted the hybrid default setting from "LimitedDetails" to "AvailabilityOnly" to avoid the impact. Alternatively, disabling the Organization Relationship feature would have also allowed users to avoid the impacted scenario. Final status: Following the reversion of the offending change and confirmation from a subset of affected users, we’ve confirmed that impact has been remediated. Scope of impact: On-premises users who attempted to view hybrid free/busy information for Exchange Online users may have been impacted. Start time: Monday, October 26, 2026, at 7:41 PM UTC End time: Wednesday, November 4, 2026, at 1:00 AM UTC Root cause: A recent service change contained a code regression and was resulting in inconsistent results when users viewed the hybrid free/busy information for Exchange Online users. Next steps: - We’re continuing to analyze how the recent service change was applied to understand why the potential for impact wasn't caught during the update testing and validation phase. These actions will help us to clarify what actions we can take to ensure similar impact doesn't occur in the future and to continue our ongoing mission to improve the resilience of our service for all Exchange Online users. This is the final update for the event.

Title: On-premises users may see inconsistent results when viewing the hybrid free/busy information for Exchange Online users User impact: On-premises users may see inconsistent results when viewing the hybrid free/busy information for Exchange Online users. More info: While we investigate this issue, we recommend adjusting the hybrid default setting from "LimitedDetails" to "AvailabilityOnly" to avoid the impact. Alternatively, disabling the Organization Relationship feature will also avoid the impact. Current status: Our review of recent service changes has led us to suspect that a recent service change contains a code regression and is resulting in impact. We’re in the process of reverting the potentially offending change and reaching out to a subset of affected users to validate whether additional mitigative actions will be required. Scope of impact: On-premises users attempting to view hybrid free/busy information for Exchange Online users may be impacted. This section may be updated as our investigation continues. Next update by: Wednesday, November 4, 2026, at 5:00 AM UTC

Title: On-premises users may see inconsistent results when viewing the hybrid free/busy information for Exchange Online users User impact: On-premises users may see inconsistent results when viewing the hybrid free/busy information for Exchange Online users. More info: While we investigate this issue, we recommend adjusting the hybrid default setting from "LimitedDetails" to "AvailabilityOnly" to avoid the impact. Alternatively, disabling the Organization Relationship feature will also avoid the impact. Current status: We're continuing our review of the event trace logs provided by a subset of affected users, as well as recent service changes, to determine the root cause and a strategy that remediates impact. Scope of impact: On-premises users attempting to view hybrid free/busy information for Exchange Online users may be impacted. This section may be updated as our investigation continues. Next update by: Wednesday, November 4, 2026, at 2:00 AM UTC

Title: On-premises users may see inconsistent results when viewing the hybrid free/busy information for Exchange Online users User impact: On-premises users may see inconsistent results when viewing the hybrid free/busy information for Exchange Online users. More info: While we investigate this issue, we recommend adjusting the hybrid default setting from "LimitedDetails" to "AvailabilityOnly" to avoid the impact. Alternatively, disabling the Organization Relationship feature will also avoid the impact. Current status: We're continuing our review of the event trace logs provided by a subset of affected users, as well as recent service changes, to determine the root cause and a strategy that remediates impact. Scope of impact: On-premises users attempting to view hybrid free/busy information for Exchange Online users may be impacted. This section may be updated as our investigation continues. Next update by: Wednesday, November 4, 2026, at 2:00 AM UTC

Title: On-premises users may see inconsistent results when viewing the hybrid free/busy information for Exchange Online users User impact: On-premises users may see inconsistent results when viewing the hybrid free/busy information for Exchange Online users. More info: While we investigate this issue, we recommend adjusting the hybrid default setting from "LimitedDetails" to "AvailabilityOnly" to avoid the impact. Alternatively, disabling the Organization Relationship feature will also avoid the impact. Current status: We're continuing our review of the event trace logs provided by a subset of affected users, as well as recent service changes, to determine the root cause and a strategy that remediates impact. Scope of impact: On-premises users attempting to view hybrid free/busy information for Exchange Online users may be impacted. This section may be updated as our investigation continues. Next update by: Wednesday, November 4, 2026, at 2:00 AM UTC

Title: On-premises users see inconsistent results when viewing the hybrid free/busy information for Exchange Online users User impact: On-premises users see inconsistent results when viewing the hybrid free/busy information for Exchange Online users. More info: While we investigate this issue, we recommend adjusting the hybrid default setting from "LimitedDetails" to "AvailabilityOnly" to avoid the impact. Current status: We're reviewing the event trace logs provided by a subset of affected users, as well as recent service changes, to determine the source of this issue so we can develop steps towards impact remediation. Scope of impact: Your organization is affected by this event, and on-premises users attempting to view hybrid free/busy information for Exchange Online users are impacted. This section may be updated as our investigation continues. Next update by: Wednesday, November 4, 2026, at 8:30 PM UTC