Some users may be unable to access custom add-ins through any Exchange Online connection method

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may have been unable to access custom add-ins through any Exchange Online connection method. More info: For additional guidance on managing Exchange Web Services, please refer to the following: https://learn.microsoft.com/en-us/exchange/client-developer/exchange-web-services/how-to-control-access-to-ews-in-exchange Final status: We’ve identified that a recent Exchange Web Services (EWS) deprecation update and an Exchange Online authentication change prevented users from accessing custom add-ins in Outlook. To remediate this issue, we rolled back both offending changes and verified through service monitoring that this action successfully resolved the impact. Admins that have disabled EWS may continue to experience this issue and we recommend that admins re-enable EWS at this time. For additional guidance on managing Exchange Web Services, please refer to the following: https://learn.microsoft.com/en-us/exchange/client-developer/exchange-web-services/how-to-control-access-to-ews-in-exchange Scope of impact: Some users who are attempted to access custom add-ins through all Exchange Online connection methods may have been impacted. Start time: Thursday, March 12, 2026, at 10:04 PM UTC End time: Friday, March 27, 2026, at 1:40 AM UTC Root cause: A recent EWS deprecation update and an Exchange Online authentication change prevented users from accessing custom add-ins in Outlook. Next steps: - We’re reviewing how the impacting changes prevented users from accessing custom add-ins so we can avoid similar issues in the future, as EWS is slated to be deprecated by October 2026. This is the final update for the event.

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. More info: For additional guidance on managing Exchange Web Services, please refer to the following: https://learn.microsoft.com/en-us/exchange/client-developer/exchange-web-services/how-to-control-access-to-ews-in-exchange Current status: We're continuing to validate our suspected root cause as mentioned in our previous communication update, and we recommend following the guidance in the "More Info" section to verify that Exchange Web Services access is enabled. Once enabled, we request that impacted users validate whether the custom add-ins are accessible. If impact persists for users after enabling this, please contact us through your support case for further investigation. Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues. Next update by: Tuesday, March 31, 2026, at 9:00 PM UTC

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. More info: For additional guidance on managing Exchange Web Services, please refer to the following: https://learn.microsoft.com/en-us/exchange/client-developer/exchange-web-services/how-to-control-access-to-ews-in-exchange Current status: We identified that a recent service update is affecting Exchange Web Services which impacts add-ins in Exchange Online. While we continue our investigation to confirm this theory, we recommend following the guidance in the "More Info" section to verify that Exchange Web Services access is enabled and then testing to validate whether the customer add-ins are accessible. Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues. Next update by: Monday, March 30, 2026, at 9:00 PM UTC

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. Current status: We've been unable to confirm that a traffic imbalance is preventing access to the affected add-ins. We're collecting enhanced trace logs and looking into recent changes in the code path to identify the root cause and a strategy that remediates impact. Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues. Next update by: Saturday, March 28, 2026, at 9:00 PM UTC

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. Current status: We're investigating the possibility that incoming traffic may not be appropriately balanced throughout the affected environment while also continuing to review the previously identified exception to determine the root cause and a strategy that remediates impact. Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues. Next update by: Friday, March 27, 2026, at 9:00 PM UTC

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. Current status: While we haven't confirmed a viable workaround, we've identified an authentication-related exception which may be contributing to the impact, and we're further reviewing this exception to aid in our root cause analysis. Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues. Next update by: Thursday, March 26, 2026, at 9:00 PM UTC

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. Current status: We're working to test some additional service configuration changes with a subset of impacted users that we anticipate may be able to alleviate the impact and assist us in confirming the underlying root cause. Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues. Next update by: Wednesday, March 25, 2026, at 9:00 PM UTC

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. Current status: As we progress with our root cause analysis and confirm the source for this event, we're working with some reporting users to test a potential workaround that may remediate the impact.  Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues. Next update by: Wednesday, March 25, 2026, at 9:30 PM UTC

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. Current status: We're finalizing our analysis of the latest collected logging in parallel with our review of recent service changes to gain further insight into the source of impact and determine our next steps. Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues. Next update by: Tuesday, March 24, 2026, at 6:00 PM UTC

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. Current status: We're continuing to analyze recent service changes that may be causing or contributing to impact while exploring what additional logging and data may be needed in order to further our investigation and isolate a potential root cause. Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues. Next update by: Tuesday, March 24, 2026, at 2:30 AM UTC

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. Current status: Our review of the available HAR logs from working and non-working users has been inconclusive in identifying the cause of this issue. Additionally, our review of impacted users' configurations for this specific add-in didn't uncover why this problem is occurring. We're reviewing recent service changes as well as reassessing what additional logging is needed to further the investigation. Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues. Next update by: Monday, March 23, 2026, at 9:30 PM UTC

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. Current status: We're continuing to analyze HAR logs from working and non-working users while we while conduct a deeper review of impacted users' configurations for this specific add-in to isolate a root cause for this issue and determine our next troubleshooting steps. Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues. Next update by: Monday, March 23, 2026, at 7:30 PM UTC

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. Current status: We're analyzing provided data from impacted users, including HTTP Archive format (HAR) logs, while reviewing the specific add-in configurations to troubleshoot this issue and determine our next steps. Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues. Next update by: Monday, March 23, 2026, at 5:30 PM UTC

Title: Some users may be unable to access custom add-ins through any Exchange Online connection method User impact: Users may be unable to access custom add-ins through any Exchange Online connection method. Current status: We're investigating a potential issue with Exchange Online where some users can't access a specific add-in through any connection method. We're checking for impact to your organization and will provide an update in 30 minutes.