Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may experience delays when accessing their Exchange Online mailboxes via one or more connection methods – ONGOING

19/05/2026 09:00:00 AM

NHSmail Reference: INC46829922

Microsoft Reference: EX1314710

Issue Status: ONGOING

Issue Description: Some users may experience delays when accessing their Exchange Online mailboxes via one or more connection methods.

More info: Impacted connection methods include but may not be limited to:

– Outlook on the web
– Outlook desktop client

Current Update: 19/05/2026 09:00:00 AM–Microsoft’s review of the mailbox infrastructure telemetry logs continues to help determine their next steps in restoring the affected portion of service infrastructure back to normal health.

Scope of impact: This issue may prevent any user in the United Kingdom from accessing their Exchange Online mailboxes via the connection methods listed in the More info section of this communication. This information may be updated as our investigation continues.

Root cause: A large influx of service traffic has caused a subset of service infrastructure to drop below our manageable service performance thresholds, resulting in impact.

Next update by: Tuesday, May 19, 2026, at 9:00 AM UTC