Some users may be unable to view on-premises or cross-tenant free/busy availability when scheduling meetings

Title: Some users may be unable to view on-premises or cross-tenant free/busy availability when scheduling meetings User impact: Users may have been unable to view on-premises or cross-tenant free/busy availability when scheduling meetings. Final status: We've received confirmation from several users who initially reported the issue that the fix was successful and the impact is remediated. Scope of impact: Impact was specific to some users that attempted to view free/busy availability. Start time: Tuesday, May 05, 2026, at 3:00 PM UTC End time: Monday, May 11, 2026, at 6:11 PM UTC Root cause: A recent service update incorrectly enabled a new authentication pathway that hadn’t yet been fully validated and led to failures in processing on-premises or cross-tenant free/busy availability requests. Next steps: - We're further reviewing the recent update to understand how the new authentication pathway was incorrectly enabled, and to understand what prevented it from being detected in our update testing and validation procedures, which will allow us to prevent similar issues in future updates. This is the final update for the event.

Title: Some users may be unable to view on-premises or cross-tenant free/busy availability when scheduling meetings User impact: Users may be unable to view on-premises or cross-tenant free/busy availability when scheduling meetings. More info: Cross-tenant or on-premises free/busy lookups via the Outlook Scheduling Assistant fail for attendees in a specific domain. As a result, availability consistently appears as “Unknown,” preventing effective meeting scheduling. Current status: Current status: We've completed reverting the offending update, and we're reaching out to some users who initially reported the issue to validate that the impact is remediated. Scope of impact: Impact is specific to some users attempting to view free/busy availability. This information may be updated as our investigation continues. Start time: Tuesday, May 05, 2026, at 3:00 PM UTC Root cause: Root cause: A recent service update incorrectly enabled a new authentication pathway that hadn’t yet been fully validated, leading to failures in processing on-premises or cross-tenant free/busy availability requests. Next update by: Tuesday, May 12, 2026, at 7:00 AM UTC

Title: Some users may be unable to view on-premises or cross-tenant free/busy availability when scheduling meetings User impact: Users may be unable to view on-premises or cross-tenant free/busy availability when scheduling meetings. More info: Cross-tenant or on-premises free/busy lookups via the Outlook Scheduling Assistant fail for attendees in a specific domain. As a result, availability consistently appears as “Unknown,” preventing effective meeting scheduling. Current status: We’ve identified a recent service update inadvertently enabled a new authentication pathway that had not yet been fully validated, leading to failures in processing requests. We’re reverting the offending update and backporting the fix across the affected environments to restore normal request processing, and we expect to share a completion timeline when one becomes available. Scope of impact: Impact is specific to some users attempting to view free/busy availability. This information may be updated as our investigation continues. Root cause: A recent service update inadvertently enabled a new authentication pathway that had not yet been fully validated, leading to failures in processing requests. Next update by: Friday, May 15, 2026, at 12:00 AM UTC

Title: Some users may be unable to view on-premises or cross-tenant free/busy availability when scheduling meetings User impact: Users may be unable to view on-premises or cross-tenant free/busy availability when scheduling meetings. More info: Cross-tenant or on-premises free/busy lookups via the Outlook Scheduling Assistant fail for attendees in a specific domain. As a result, availability consistently appears as “Unknown,” preventing effective meeting scheduling. Current status: We've isolated that impact is not limited to users in the Asia Pacific region, and we've updated the "Scope of impact" field of our communications to reflect this. We're working with a subset of affected users to schedule a debugging session to collect additional logging during a reproduction of impact to assist with furthering our root cause analysis. Scope of impact: Impact is specific to some users attempting to view free/busy availability. This information may be updated as our investigation continues. Next update by: Tuesday, May 12, 2026, at 12:00 AM UTC

Title: Users may be unable to view on-premises or cross-tenant free/busy availability when scheduling meetings User impact: Users may be unable to view on-premises or cross-tenant free/busy availability when scheduling meetings. More info: Cross-tenant or on-premises free/busy lookups via the Outlook Scheduling Assistant fail for attendees in a specific domain. As a result, availability consistently appears as “Unknown,” preventing effective meeting scheduling. Current status: We're continuing our efforts at gathering samples from a subset of affected users who are able to reproduce the issue to further our investigative actions. Scope of impact: Impact is specific to some users in Asia Pacific attempting to view free/busy availability. This information may be updated as our investigation continues. Next update by: Sunday, May 10, 2026, at 10:00 PM UTC

Title: Users may be unable to view on-premises or cross-tenant free/busy availability when scheduling meetings User impact: Users may be unable to view on-premises or cross-tenant free/busy availability when scheduling meetings. More info: Cross-tenant or on-premises free/busy lookups via the Outlook Scheduling Assistant fail for attendees in a specific domain. As a result, availability consistently appears as “Unknown,” preventing effective meeting scheduling. Current status: We're gathering traces from a subset of affected users for reproducing the issue to assist us with our investigation. Scope of impact: Impact is specific to some users in Asia Pacific attempting to view free/busy availability. Next update by: Sunday, May 10, 2026, at 1:00 AM UTC

Title: Users are unable to view free/busy availability for attendees in a specific domain when scheduling meetings User impact: Users are unable to view free/busy availability for attendees in a specific domain when scheduling meetings. More info: Cross-tenant free/busy lookups via the Outlook Scheduling Assistant fail for attendees in a specific domain. As a result, availability consistently appears as “Unknown,” preventing effective meeting scheduling. Current status: We're reviewing HTTP Archive format (HAR) logs to isolate the source of the issue and formulate a mitigation plan. Scope of impact: Your organization is affected by this event, and some users attempting to view free/busy availability are impacted. Next update by: Tuesday, May 12, 2026, at 1:00 AM UTC

Title: Users are unable to view free/busy availability for attendees in a specific domain when scheduling meetings User impact: Users are unable to view free/busy availability for attendees in a specific domain when scheduling meetings. More info: Cross-tenant free/busy lookups via the Outlook Scheduling Assistant fail for attendees in a specific domain. As a result, availability consistently appears as “Unknown,” preventing effective meeting scheduling. Current status: We’re reviewing associated support case details to understand more about the issue, and determine our next troubleshooting steps. Scope of impact: Your organization is affected by this event, and some users attempting to view free/busy availability are impacted. Next update by: Saturday, May 09, 2026, at 9:30 AM UTC