Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may have experienced issues when accessing their Exchange Online mailbox via one or more connection method – RESOLVED

17/03/2026 08:21:00 AM

NHSmail Reference: INC46774573

Microsoft Reference: EX1253275

Issue Status: RESOLVED

Issue Description: Users may have experienced errors when accessing their mailbox via multiple Exchange Online connection methods.

More info: Users may have experienced errors or failures when attempting to access their mailbox. Impacted connection methods included, but were not limited to:

– Outlook on the web
– Outlook desktop
– Exchange ActiveSync
– Other Exchange Online connection protocols

Final Update: 17/03/2026 08:21:00 AM –Microsoft has confirmed that service has remained healthy for an extended period of time. Our monitoring indicates the issue is no longer occurring for the affected users.

Scope of impact: Impact was specific to some users attempting to access their mailbox via any of the connection methods detailed above.

Preliminary root cause: An underlying issue involving the supporting network infrastructure resulted in a service availability degradation across the Exchange Online connection methods. They are continuing to investigate to determine the full root cause and will provide more information within the Post-Incident Report.

Next steps: Microsoft has continuing to examine the underlying circumstances that led to this behavior to understand the root cause.

They will provide a preliminary Post-Incident Report within two business days and a final Post-Incident Report within five business days.