Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may be intermittently unable to access their Exchange Online mailboxes in some connection methods – ONGOING

20/03/2026 08:40:00 AM

NHSmail Reference: INC46778121

Microsoft Reference: EX1256020

Issue Status: ONGOING

Issue Description: Users may be intermittently unable to access their Exchange Online mailboxes in some connection methods.

More info: This issue may intermittently impact some users who are attempting to access the Exchange Online service through the Outlook mobile apps or the new Outlook for Mac desktop client.

Final Update: 20/03/2026 08:44:00 AM – Microsoft has identified that restarting the affected infrastructure isn’t a sufficient fix for this issue and they are continuing their investigation to identify and validate an appropriate remediation action. Once available, they will provide a timeline for resolution.

Scope of impact: Impact may occur for some users intermittently and users may be unable to access their Exchange Online mailboxes with the Outlook mobile apps.

Root cause: A recent change within the Exchange Online service intended to introduce a new virtual account resulted in impact.

Next update by: Friday, March 20, 2026, at 6:30 PM UTC