💡 Our Technical Review in summary
1. Summary
A compatibility issue has been identified between Classic Outlook and the Microsoft Teams Meeting Add-in (version 26043.2016.4478.2773). A code issue in a recent update to the add-in is causing functionality failures when used with older versions of the Outlook desktop client.
2. Impact
Impacted users may experience the following symptoms when the Teams Meeting Add-in is enabled:
- Frequent crashes while using Classic Outlook.
- Inability to launch the Outlook application.
The issue specifically affects the Win32 Classic Outlook client utilizing Teams Add-in version 26043.2016.4478.2773.
3. Status
Current State: Service Degradation / Mitigation Advised.
Microsoft has determined that a standard service-side fix is not viable due to the incompatibility being rooted in outdated Outlook versions. To resolve this issue, IT Admins should take the following actions:
- Primary Resolution: Upgrade affected users to the latest version of Classic Outlook (Win32).
- Alternative: If additional time is required before upgrading, contact Microsoft support representatives to request a temporary version reversion.
- Verified Version: Microsoft has confirmed that Teams version 26032.208.4399.5 remains compatible with older Outlook builds.
The next scheduled update from Microsoft is expected by Monday, March 30, 2026.
Microsoft Official Issue Details
User Impact
Users may be unable to use classic Outlook when the Teams Meeting Add-in is enabled.
Status: serviceDegradation
Service: Exchange Online
Classification: incident
Origin: microsoft
Updates
- 2026-03-23 10:02
Title: Some users may be unable to use classic Outlook when the Teams Meeting Add-in is enabledUser impact: Users may be unable to use classic Outlook when the Teams Meeting Add-in is enabled.
More info: Specifically, impacted users may experience crashes while using the classic Outlook on any client, or be unable to launch the service. While we work on the permanent fix, we recommend impacted users upgrade to the latest Outlook version.
A code issue within a recent Microsoft Teams Meeting Add-in update under version 26043.2016.4478.2773, is causing a compatibility issue with classic Outlook, and resulting in functionality issues. We’ve confirmed that the previous Microsoft Teams version 26032.208.4399.5 works successfully with classic Outlook, though we recommend affected users that are on the latest updated Microsoft Teams version to also upgrade to the latest Outlook version to avoid further complications.
Current status: We’ve determined that the aforementioned fix isn’t a viable option due to impact occurring due to outdated versions causing the incompatibility and recommend if you’re affected by this event that you update to the latest Classic OutlookWin32 version. However, please reach out to your support representatives to request a temporary reversion if you require additional time to upgrade your Outlook version.
Scope of impact: Some users that are attempting to use classic Outlook with the Microsoft Teams Meeting Add-in version 26043.2016.4478.2773 enabled may be impacted. This information may be updated as our investigation continues.
Start time: Thursday, March 12, 2026, at 12:36 PM UTC
Root cause: A code issue within a recent Microsoft Teams Meeting Add-in update under version 26043.2016.4478.2773 is causing a compatibility issue with classic Outlook and resulting in functionality issues.
Next update by: Monday, March 30, 2026, at 10:30 AM UTC
- 2026-03-19 10:25
Title: Some users may be unable to use classic Outlook when the Teams Meeting Add-in is enabledUser impact: Users may be unable to use classic Outlook when the Teams Meeting Add-in is enabled.
More info: Specifically, impacted users may experience crashes while using the classic Outlook on any client, or be unable to launch the service. While we work on the permanent fix, we recommend impacted users upgrade to the latest Outlook version.
A code issue within a recent Microsoft Teams Meeting Add-in update under version 26043.2016.4478.2773, is causing a compatibility issue with classic Outlook, and resulting in functionality issues. We’ve confirmed that the previous Microsoft Teams version 26032.208.4399.5 works successfully with classic Outlook, though we recommend affected users that are on the latest updated Microsoft Teams version to also upgrade to the latest Outlook version to avoid further complications.
Current status: We’re continuing to work on deploying a fix to resolve the compatibility issue, and anticipate that this should be complete by our next scheduled update.
Scope of impact: Some users that are attempting to use classic Outlook with the Microsoft Teams Meeting Add-in version 26043.2016.4478.2773 enabled may be impacted. This information may be updated as our investigation continues.
Start time: Thursday, March 12, 2026, at 12:36 PM UTC
Root cause: A code issue within a recent Microsoft Teams Meeting Add-in update under version 26043.2016.4478.2773 is causing a compatibility issue with classic Outlook and resulting in functionality issues.
Next update by: Monday, March 23, 2026, at 10:30 AM UTC
- 2026-03-17 08:54
Title: Some users may be unable to use classic Outlook when the Teams Meeting Add-in is enabledUser impact: Users may be unable to use classic Outlook when the Teams Meeting Add-in is enabled.
More info: Specifically, impacted users may experience crashes while using the classic Outlook on any client, or be unable to launch the service. While we work on the permanent fix, we recommend impacted users upgrade to the latest Outlook version.
Current status: We’ve identified a code issue within a recent Microsoft Teams Meeting Add-in update under version 26043.2016.4478.2773, which is causing a compatibility issue with classic Outlook, and resulting in functionality issues. We’ve confirmed that the previous Microsoft Teams version 26032.208.4399.5 works successfully with classic Outlook, though we recommend affected users that are on the latest updated Microsoft Teams version to also upgrade to the latest Outlook version to avoid further complications. We’re working on deploying a fix to resolve the compatibility issue, and we anticipate being able to provide a remediation timeline by our next scheduled update.
Scope of impact: Some users that are attempting to use classic Outlook with the Microsoft Teams Meeting Add-in version 26043.2016.4478.2773 enabled may be impacted. This information may be updated as our investigation continues.
Start time: Thursday, March 12, 2026, at 12:36 PM UTC
Root cause: A code issue within a recent Microsoft Teams Meeting Add-in update under version 26043.2016.4478.2773 is causing a compatibility issue with classic Outlook and resulting in functionality issues.
Next update by: Thursday, March 19, 2026, at 10:30 AM UTC
- 2026-03-17 06:55
Title: Some users may be unable to use classic Outlook when the Teams Meeting Add-in is enabledUser impact: Users may be unable to use classic Outlook when the Teams Meeting Add-in is enabled.
More info: Specifically, impacted users may experience crashes while using the classic Outlook on any client, or be unable to launch the service. While we work on the permanent fix, we recommend impacted users upgrade to the latest Outlook version.
As a workaround, users can also perform an Online Repair of Office or update Outlook to the latest version to resolve the issue.
Current status: We’re analyzing support provided information to determine our next troubleshooting steps.
Scope of impact: Some users that are attempting to use classic Outlook with the Microsoft Teams Meeting Add-in version 26043.2016.4478.2773 enabled may be impacted. This information may be updated as our investigation continues.
Next update by: Tuesday, March 17, 2026, at 9:00 AM UTC
