Users were intermittently unable to access Exchange Online

Title: Users were intermittently unable to access Exchange Online User impact: Users were intermittently unable to access Exchange Online. More info: Users experienced intermittent failures when attempting to access their mailbox, including sign-in failures and connection errors. This impact occurred across various connection methods and client experiences, where access attempts did not complete successfully or timed out. Final status: We’ve confirmed after a period of monitoring, that the impacted infrastructure self-restored, and service has returned to expected performance levels. We'll closely monitor the service to ensure that it remains healthy. Scope of impact: Impact was specific to some users served through the affected infrastructure in the Exchange Online service, attempting to access their mailboxes. Start time: Sunday, May 24, 2026, at 11:00 PM UTC End time: Monday, May 25, 2026, at 7:15 AM UTC Root cause: A service issue following an authentication activity led to a condition that disrupted normal authentication behavior and access to Exchange Online. Next steps: We're analyzing performance data and trends on the affected infrastructure to help prevent this problem from happening again. This is the final update for this event.

Title: Users may intermittently be unable to access Exchange Online User impact: Users may intermittently be unable to access Exchange Online. Current status: We've confirmed that impact began shortly after certain authentication components stopped functioning as expected. We're furthering our investigation on the diagnostic data to help determine our path towards remediation to restore the affected authentication components. Scope of impact: This issue may impact users worldwide that are routed through the impacted infrastructure. This information may be updated as our investigation continues. Start time: Sunday, May 24, 2026, at 11:00 PM UTC Root cause: A portion of the structured query language infrastructure responsible for accessing Exchange Online isn't performing as efficiently as expected, resulting in impact. Next update by: Monday, May 25, 2026, at 8:30 AM UTC

Title: Users may intermittently be unable to access Exchange Online User impact: Users may intermittently be unable to access Exchange Online. Current status: In an attempt to alleviate impact, we've restarted some of the affected infrastructure with mixed results. We're continuing our root cause investigation using all available diagnostic data to help determine our next steps towards remediation. Scope of impact: This issue may impact users worldwide that are routed through the impacted infrastructure. This information may be updated as our investigation continues. Start time: Sunday, May 24, 2026, at 11:00 PM UTC Root cause: A portion of the structured query language infrastructure responsible for accessing Exchange Online isn't performing as efficiently as expected, resulting in impact. Next update by: Monday, May 25, 2026, at 6:30 AM UTC

Title: Users may intermittently be unable to access Exchange Online User impact: Users may intermittently be unable to access Exchange Online. Current status: We've confirmed that faulty authentication components within the infrastructure caused impact. We're developing and deploying a fix we anticipate will alleviate impact. Scope of impact: This issue may impact users worldwide that are routed through the impacted infrastructure. This information may be updated as our investigation continues. Start time: Sunday, May 24, 2026, at 11:00 PM UTC Root cause: A portion of the structured query language infrastructure responsible for accessing Exchange Online isn't performing as efficiently as expected, resulting in impact. Next update by: Monday, May 25, 2026, at 4:30 AM UTC

Title: Users may intermittently be unable to access Exchange Online User impact: Users may intermittently be unable to access Exchange Online. Current status: We were alerted that a portion of the SQL infrastructure responsible for accessing Exchange Online isn't performing as efficiently as expected which resulted in impact. We're investigating different troubleshooting methods to alleviate impact. Scope of impact: This issue may impact users worldwide that are routed through the impacted infrastructure. This information may be updated as our investigation continues. Start time: Sunday, May 24, 2026, at 11:00 PM UTC Root cause: A portion of the structured query language infrastructure responsible for accessing Exchange Online isn't performing as efficiently as expected, resulting in impact. Next update by: Monday, May 25, 2026, at 2:30 AM UTC

Title: Potential issues accessing mailboxes via one or more connection methods User impact: Users may experience errors or failures when accessing their mailbox via one or more Exchange Online connection methods. Current status: We're investigating a potential issue and checking for impact to your organization. We'll provide an update within 60 minutes.