Microsoft is addressing a known issue causing the classic Outlook client for Windows to crash immediately upon launch. This problem affects Microsoft 365 users, and the company states that the only current solution is to contact Exchange Online support through the admin portal. After a support case is opened, the service team will implement a change to mitigate the crashing.
The error message indicates that Outlook cannot start and that logging into the Exchange account has failed. Microsoft suggests users can temporarily switch to the new Outlook for Windows or use Outlook Web Access (OWA) to access their email. While the root cause is under investigation, users can help confirm the issue by checking for a specific authentication concurrency error in a Fiddler trace.
This is not the first problem to plague the classic Outlook client this year, following previous bugs related to high CPU usage and broken drag-and-drop functionality. Standard troubleshooting steps, like starting in safe mode or creating a new profile, are not effective for this particular problem, underscoring its complexity and server-side nature.
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