Resolved after 4 hours 43 minutes, affecting Outlook Add-in, on December 4, 2025.
## Description The Outlook 365 Add-in for Classic Outlook encountered connection issue \(Error 503\) where email signatures failed to load. ## Root Cause The issue was caused by an important update for the Add-in which requires Classic Outlook to restart in order to complete. ## Impact * **User Experience**: Add-in is not connecting and signatures are not inserted when composing emails. * **Business Impact**: No critical data loss or security issues. ## Resolution Users must restart Outlook app to clear the error and complete the Add-in update.
Affected components
Update timeline
- investigating Dec 04, 2025, 10:14 PM UTC
Clients may encounter connection issue with the add-in, showing error 503. We are currently investigating this issue.
- monitoring Dec 04, 2025, 10:18 PM UTC
Applied updates for the add-in caused initial connection issue with Classic Outlook. Restarting the Outlook application will fix and restore the connection. Please advise users to restart their Outlook application to clear the error.
- resolved Dec 05, 2025, 02:57 AM UTC
Incident has been resolved
- postmortem Dec 05, 2025, 02:57 AM UTC
## Description The Outlook 365 Add-in for Classic Outlook encountered connection issue \(Error 503\) where email signatures failed to load. ## Root Cause The issue was caused by an important update for the Add-in which requires Classic Outlook to restart in order to complete. ## Impact * **User Experience**: Add-in is not connecting and signatures are not inserted when composing emails. * **Business Impact**: No critical data loss or security issues. ## Resolution Users must restart Outlook app to clear the error and complete the Add-in update.
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