Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may be unable to access specific archive mailboxes – RESOLVED

Announcements Sourav Nandi

24/07/2025 09:00:00 AM

NHSmail Reference: INC46587264

Microsoft Reference: EX1102371

Issue Status: RESOLVED

Issue Description: Some users may be unable to access specific archive mailboxes.

More info: Specifically, during an archive mailbox cross-forest migration, some users may be unable to access the online archive mailbox when the primary mailbox is located in a different Active Directory forest from the archive mailbox.

Final Update: 28/10/2025 08:05:00 AM – Microsoft have confirmed the fix has completed its deployment and been activated in all environments, confirming mitigation with affected users and service telemetry.

Scope of impact: Any user attempting to access their Exchange Online archive mailbox may encounter this issue if their primary and archive mailboxes aren’t located on the same portion of Active Directory infrastructure.

Root cause: As part of routine mailbox database maintenance, the affected archive mailboxes were migrated to a separate portion of database service infrastructure from the primary, preventing users from accessing the archive mailbox and causing impact.

Next steps: Microsoft are continuing their analysis of the impacting maintenance procedures to better identify and prevent similar impact in the future.