Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app

Title: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app User impact: Users may not have been able to open email file attachments or see the "Open" option in the new Outlook desktop app. More info: Impacted users may have been presented with an error that the file can't be opened and to restart Outlook to try again; however, the "Open" option was no longer available after encountering the error. Users could have selected "Save as" to download the file and then open the attachment to bypass the impact. Final status: We've completed deployment of our targeted fix to disable the impacting configuration and confirmed with a subset of affected users that the impact is remediated as a result. Any users still impacted will need to close and reopen new Outlook for the change to take effect and resolve the issue. Scope of impact: This issue may have affected new Outlook desktop users who had upgraded to Edge version 156 and were attempting to open email file attachments or see the "Open" option in the new Outlook desktop app. Start time: Friday, October 23, 2026, at 12:00 AM UTC End time: Thursday, October 29, 2026, at 12:00 PM UTC Root cause: A recent update to Edge Version 156 unintentionally enabled an unnecessary configuration change and caused impact. Next steps: - We're reviewing our Edge version update testing and validation procedures to identify and prevent similar issues with opening email file attachments in the new Outlook desktop app from occurring during deployment in the future. This is the final update for the event.

Title: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app User impact: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app. More info: Impacted users may be presented with an error that the file can't be opened and to restart Outlook to try again; however, the "Open" option is no longer available after encountering the error. Users can select "Save as" to download the file and then open the attachment to bypass the impact. Current status: We’ve determined that a recent update to Edge Version 156 unintentionally enabled an unnecessary configuration, resulting in impact. We’ve developed and deployed a targeted fix to disable this configuration, which may take up to 12 hours to propagate across our service infrastructure. We’ll use service telemetry to confirm the fix has been applied across the infrastructure. Once confirmed, users will need to close and reopen New Outlook for the change to take effect and resolve the issue. Scope of impact: This issue affects new Outlook desktop users who have upgraded to Edge version 156. This section may be updated as our investigation continues. Root cause: A recent update to Edge Version 156 unintentionally enabled an unnecessary configuration change and is resulting in impact. Next update by: Thursday, October 29, 2026, at 8:30 PM UTC

Title: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app User impact: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app. More info: Impacted users may be presented with an error that the file can't be opened and to restart Outlook to try again; however, the "Open" option is no longer available after encountering the error. Users can select "Save as" to download the file and then open the attachment to bypass the impact. Current status: We're continuing to work on validating our root cause hypothesis and once completed, we'll determine our next steps towards remediation. Scope of impact: This issue affects new Outlook desktop users who have upgraded to Edge version 156. This section may be updated as our investigation continues. Next update by: Wednesday, October 28, 2026, at 1:30 AM UTC

Title: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app User impact: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app. More info: Impacted users may be presented with an error that the file can't be opened and to restart Outlook to try again; however, the "Open" option is no longer available after encountering the error. Users can select "Save as" to download the file and then open the attachment to bypass the impact. Current status: We're narrowing down a potential root cause that is related to a recent service-side update. We're in the process of validating this hypothesis and once confirmed will help us determine our remediation options. Scope of impact: This issue affects new Outlook desktop users who have upgraded to Edge version 156. Next update by: Wednesday, October 28, 2026, at 11:30 PM UTC

Title: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app User impact: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app. More info: Impacted users may be presented with an error that the file can't be opened and to restart Outlook to try again; however, the "Open" option is no longer available after encountering the error. Users can select "Save as" to download the file and then open the attachment to bypass the impact. Current status: We're continuing our investigation into this issue, reviewing the information provided in specific support cases as well as our own service-side reproductions of this issue in order determine the best approach for troubleshooting this issue. Scope of impact: This issue affects new Outlook desktop users who have upgraded to Edge version 156. Next update by: Wednesday, October 28, 2026, at 9:30 PM UTC

Title: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app User impact: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app. More info: Impacted users may be presented with an error that the file can't be opened and to restart Outlook to try again; however, the "Open" option is no longer available after encountering the error. Users can select "Save as" to download the file and then open the attachment to bypass the impact. Current status: We're reviewing user reports of impact and data collected from an internal reproduction of the problem to determine what's leading to this behavior, as well as our approach to addressing the impact. Scope of impact: This issue affects new Outlook desktop users who have upgraded to Edge version 156. Next update by: Wednesday, October 28, 2026, at 7:30 PM UTC

Title: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app User impact: Users may not be able to open email file attachments or see the "Open" option in the new Outlook desktop app. More info: Impacted users may be presented with an error that the file can't be opened and to restart Outlook to try again; however, the "Open" option is no longer available after encountering the error. Users can select "Save as" to download the file and then open the attachment to bypass the impact. Current status: We're investigating a potential issue with Exchange Online and checking for impact. We'll provide an update within 60 minutes.