Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may be unable to view mailbox storage data in Outlook and Outlook on the web – RESOLVED

16/07/2026 08:36:00 AM

NHS.net Connect Reference: INC46881346

Microsoft Reference: EX1428537

Issue Status: RESOLVED

Issue Description: Some users may be unable to view mailbox storage data in Outlook and Outlook on the web.

More info: Affected users are shown the following error message “Storage data is temporarily unavailable” when trying to view mailbox storage data for multiple mailboxes.

Final Update: 23/07/2026 09:42:00 AM – Microsoft has validated that their code fix has fully deployed throughout the affected environments and has successfully remediated all impact.

Scope of impact: Some users attempting to view mailbox storage data in Outlook and Outlook on the web may have been impacted.

Root cause: A recent service build introduced an unsupported property into mailbox statistics data returned by a backend process. When the service attempted to retrieve mailbox storage information, the unsupported property caused the request to fail and prevented mailbox storage data from being displayed, which resulted in impact.

Next steps: Microsoft is reviewing their service build validation and implementation processes to improve how they detect potential unsupported properties and prevent similar mailbox storage data issues from occurring in the future.