Users may be unable to access some Exchange Online archive mailboxes.
ID	Workload Feature	Title	Classification	Severity	Start Time	Last Updated
EX1102371	Exchange Online E-Mail and calendar access Database Offline - mailbox database is dismounted	Users may be unable to access some Exchange Online archive mailboxes	advisory		24-Jun-2025 08:30	18-Sep-2025 17:13
Update: 18-Sep-2025 17:13 Title: Users may be unable to access some Exchange Online archive mailboxes User Impact: Users may be unable to access some Exchange Online archive mailboxes. More Info: This issue occurs when routine mailbox database maintenance for archive mailboxes relocates the archive to a different portion of Active Directory infrastructure from the primary mailbox. Impact may persist both during the maintenance move and after the move. The problem impacts archive mailbox access through any Exchange Online connection method. Current Status: Our fix validations are progressing and scheduled to be complete by our next scheduled communication update. At said time, we're expecting a timeline for the deployment of our fix and the remediation of impact. 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. Start Time: Monday, June 23, 2025, at 1:00 PM UTC Next Update By: Thursday, October 2, 2025, at 10:30 PM UTC Update: 11-Sep-2025 16:43 Title: Users may be unable to access some Exchange Online archive mailboxes User Impact: Users may be unable to access some Exchange Online archive mailboxes. More Info: This issue occurs when routine mailbox database maintenance for archive mailboxes relocates the archive to a different portion of Active Directory infrastructure from the primary mailbox. Impact may persist both during the maintenance move and after the move. The problem impacts archive mailbox access through any Exchange Online connection method. Current Status: Our validation efforts are taking longer than initially anticipated, and we're continuing to verify the efficacy of our secondary fix within our testing environment for an extended period. We expect to have a more substantial update by Thursday, September 25, 2025, and will provide an updated timeline as one becomes available. 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. Start Time: Monday, June 23, 2025, at 1:00 PM UTC Next Update By: Thursday, September 18, 2025, at 10:30 PM UTC Update: 18-Aug-2025 15:34 Title: Users may be unable to access some Exchange Online archive mailboxes User Impact: Users may be unable to access some Exchange Online archive mailboxes. More Info: This issue occurs when routine mailbox database maintenance for archive mailboxes relocates the archive to a different portion of Active Directory infrastructure from the primary mailbox. Impact may persist both during the maintenance move and after the move. The problem impacts archive mailbox access through any Exchange Online connection method. Current Status: We've completed the validations of our secondary fix and we're deploying it to our internal test environment to further confirm its' ability to safely resolve this issue. We expect that this validation process may take until Wednesday, September 3, 2025. Once confirmed, we'll begin deploying the fix to all affected users and will provide an estimated timeline for that process once available. Scope of Impact: Any user attempting to access their Exchange Online archive mailbox may encounter this issue if their primary and archive mailbox aren't located on the same portion of Active Directory infrastructure. Start Time: Monday, June 23, 2025, at 1:00 PM UTC Next Update By: Thursday, September 11, 2025, at 10:00 PM UTC Update: 04-Aug-2025 15:05 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: Our server-side fix to update the method that users' cache is generated upon loading the affected mailboxes has completed and saturated to affected environments, but also revealed additional code discrepancies that will need to be addressed by our supplementary fix. To ensure complete remediation, the internal validations for our secondary fix's deployment has been delayed to allow for additional review and testing so we can ensure it doesn't produce any unexpected problems in the service. We aim to provide a timeline for our secondary fix deployment and the remediation of impact at the time of our next scheduled update. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Start Time: Monday, June 23, 2025, at 1:00 PM UTC Next Update By: Monday, August 18, 2025, at 8:30 PM UTC Update: 28-Jul-2025 15:28 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: Our server-side fix to update the method that users' cache is generated upon loading the affected mailboxes has completed approximately 93 percent of the necessary deployment, and we're monitoring its completion. While progressing with our root cause analysis, the internal validations for our secondary fix's deployment are also progressing so we can ensure it doesn't produce any unexpected problems in the service. We'll provide a timeline for our secondary fix deployment and the remediation of impact once they have become available. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Start Time: Monday, June 23, 2025, at 1:00 PM UTC Next Update By: Monday, August 4, 2025, at 8:30 PM UTC Update: 23-Jul-2025 16:39 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: Validation of a server-side fix to change to the way the user cache is generated upon loading the affected mailboxes is complete and has begun deploying. Validation of a second client-side fix, on which mitigation for Outlook on the web is dependent, is progressing. We're continuing to confirm the efficacy of the client-side fix, and we'll provide a timeline for deployment once this process is complete. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Monday, July 28, 2025, at 8:30 PM UTC Update: 17-Jul-2025 15:00 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: We've completed developing the previously mentioned change to the way the user cache is generated upon loading the affected mailboxes, and we're validating the change for efficacy before beginning deployment to the impacted environment. We're aiming to complete the validation process and provide an estimated timeline for deployment and remediation in our next scheduled communication update. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Wednesday, July 23, 2025, at 8:30 PM UTC Update: 15-Jul-2025 15:16 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: While we continue to investigate the source of the impact, we're developing a possible fix that will change the way user cache is generated upon loading the affected mailboxes. This fix is only being developed for Outlook on the web at this time and its efficacy will be tested before proceeding with further development. We expect to complete testing of this possible mitigation by the time of our next update. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Thursday, July 17, 2025, at 8:30 PM UTC Update: 10-Jul-2025 15:34 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: We're continuing to coordinate with affected users to complete the migration for those whose migrations were already initiated and then entered a stuck state, and in parallel we're proceeding with our efforts to create a long-term fix to prevent the mailboxes from entering the stuck state again. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Tuesday, July 15, 2025, at 8:30 PM UTC Update: 03-Jul-2025 15:55 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: We're working with affected users to complete the migration for those whose migrations were already initiated and then entered a stuck state to assist us in remediating impact for all affected users. Simultaneously, we're working internally to create a fix that will prevent similar impact scenarios from occurring in future. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Thursday, July 10, 2025, at 8:30 PM UTC Update: 26-Jun-2025 14:55 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: We're preparing to initiate the operation to expedite the impacted migration while we continue to coordinate with affected users to obtain the previously mentioned list of priority users. In parallel, we're preparing a secondary operation to revert the migration for users whose migrations were already initiated and then entered a stuck state to assist us in remediating impact for all affected users. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Thursday, July 3, 2025, at 8:30 PM UTC Update: 25-Jun-2025 15:28 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: We're working with your representatives to confirm a list of priority users who need their mailbox migration expedited along with discussing potential mitigation paths while we work to investigate and confirm the underlying issue. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Thursday, June 26, 2025, at 8:30 PM UTC Update: 24-Jun-2025 19:43 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: We've completed the pause of the mailbox migration and we're continuing to work with impacted users to confirm a list of priority users who need their mailbox migration expedited, and to discuss our remediation strategy. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Wednesday, June 25, 2025, at 8:00 PM UTC Update: 24-Jun-2025 16:35 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: We're pausing the current mailbox migration for some users while we work with them to discuss potential mitigation paths. Simultaneously, we're confirming a list of priority users who need their mailbox migration expedited to bypass high impact scenarios while we work to investigate and confirm the underlying root cause of impact. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Wednesday, June 25, 2025, at 1:00 AM UTC Update: 24-Jun-2025 14:43 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: We're working with some affected users to discuss potential mitigation paths and what actions we can take to resolve impact for affected users while we work to investigate and resolve the underlying root cause. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Tuesday, June 24, 2025, at 9:00 PM UTC Update: 24-Jun-2025 12:51 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: Our process to move the affected archive and primary mailboxes to the same forest to alleviate impact in the short term is ongoing and we aim to provide a timeline for this migration as one becomes available. Simultaneously, we're analyzing Fiddler traces for working and non-working mailbox authentication requests to better understand the underlying root cause and what steps we can take to resolve impact. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Tuesday, June 24, 2025, at 7:00 PM UTC Update: 24-Jun-2025 10:32 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: While we progress with our analysis of diagnostic data to isolate the root cause, we've initiated a process to manually relocate the archive and primary mailboxes to the same forest to alleviate impact in the short term. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Tuesday, June 24, 2025, at 5:00 PM UTC Update: 24-Jun-2025 08:49 Title: Some users may be unable to access specific archive mailboxes User Impact: 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. Current Status: We're analyzing provided server and HTTP Archive format (HAR) logs to isolate the root cause and formulate a mitigation plan. Scope of Impact: Some users attempting to access specific archive mailboxes during a migration may be impacted. Next Update By: Tuesday, June 24, 2025, at 3:00 PM UTC