Outlook not opening - Confirmed Microsoft bug with Teams.

[TheRobins]

Just FYI, we are using 2021 LTSC here and no one can open outlook at all.

 

Some users may be unable to use classic Outlook when the Teams Meeting Add-in is enabled

Issue ID: EX1254044
Affected services: Exchange Online
Status: Service degradation
Issue type: Incident
Start time: 12 Mar 2026, 12:36 GMT

User 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.

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.

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.

Current status
17 Mar 2026, 08:54 GMT
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.
Next update by:
Thursday, 19 March 2026 at 10:30 GMT

[Fazza]

Until you get a fix, have you tried holding down the CTRL key and then clicking/double-clicking on the Outlook icon?

 

 

Safe mode should open Outlook without any add-ins running so maybe it will open for you.

[TheRobins]

Sadly not, they have done a good job on breaking it. Even removing teams and the add-in will not work as the damage is already done. 

[BigAndyD]

Has this been resolved yet? We are getting a number of users complaining.

[TheRobins]

All good this morning for us, wasnt working last thing on Friday when I checked. I didnt do anything or have any updates to apply, possibly it was infrastructrure side they rolled the update out. to?>

[TheRobins]

Further, a new update on 365 Admin page.

 

"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."

 

Worth triggering a click to run update on the affected machines?

[Gongalong]

We have very few staff using the Outlook app, but had a case this morning. We uninstalled and relnstalled the latest, and that resolved it. Not great though if you have lots of staff using the app. Some further workarounds in the support article https://support.microsoft.com/en-gb/office/classic-outlook-crashes-and-opens-in-safe-mode-starting-march-12-2026-0f1b0427-e259-438d-aa93-78128ae61f80

[MrEprise]

This fix seems to work and doesn't require re-installing or updating Office.

 

Quote

The Teams add-in version installed here:

1.26.02603

is known to get corrupted when Microsoft Teams updates.

Fix by reinstalling it:

1. Close Outlook and Teams
2. Delete this folder:

       C:\Users\%username%\AppData\Local\Microsoft\TeamsMeetingAdd-in

3. Start Teams again
4. Teams will reinstall the add-in automatically.

[MatthewL]

Had a few of these last week, just went into Word or Excel and ran updates and let it complete and it fixes it.

[BigAndyD]

Just had another report today