Microsoft 365 classic Outlook crashes on launch

First reported

01.10.2025 21:43

Last updated

1 unique sources, 1 articles

Summary

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Microsoft 365 customers using classic Outlook on Windows systems are experiencing crashes upon launch. The issue requires Exchange Online support intervention to mitigate. Users see an error message stating that Outlook cannot start and that logging into the Exchange account has failed. Microsoft is investigating the root cause and has provided a temporary workaround using the new Outlook for Windows or Outlook Web Access (OWA).

Timeline

01.10.2025 21:43 1 articles · 4h ago

Microsoft 365 classic Outlook crashes on launch
Microsoft 365 customers using classic Outlook on Windows systems are experiencing crashes upon launch. The issue requires Exchange Online support intervention to mitigate. Users see an error message stating that Outlook cannot start and that logging into the Exchange account has failed. Microsoft is investigating the root cause and has provided a temporary workaround using the new Outlook for Windows or Outlook Web Access (OWA).
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New bug in classic Outlook can only be fixed via Microsoft support — www.bleepingcomputer.com — 01.10.2025 21:43
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Information Snippets

The issue impacts Microsoft 365 customers using classic Outlook on Windows systems.
First reported: 01.10.2025 21:43

1 source, 1 article
Show sources
- New bug in classic Outlook can only be fixed via Microsoft support — www.bleepingcomputer.com — 01.10.2025 21:43
The error message indicates that Outlook cannot start and that logging into the Exchange account has failed.
First reported: 01.10.2025 21:43

1 source, 1 article
Show sources
- New bug in classic Outlook can only be fixed via Microsoft support — www.bleepingcomputer.com — 01.10.2025 21:43
Affected users are advised to open a support case from the Microsoft 365 Admin portal to request a service change.
First reported: 01.10.2025 21:43

1 source, 1 article
Show sources
- New bug in classic Outlook can only be fixed via Microsoft support — www.bleepingcomputer.com — 01.10.2025 21:43
Microsoft suggests capturing a Fiddler trace to confirm the error 'LID: 49586 - Authentication concurrency limit is reached.'
First reported: 01.10.2025 21:43

1 source, 1 article
Show sources
- New bug in classic Outlook can only be fixed via Microsoft support — www.bleepingcomputer.com — 01.10.2025 21:43
Temporary workarounds include using the new Outlook for Windows or Outlook Web Access (OWA).
First reported: 01.10.2025 21:43

1 source, 1 article
Show sources
- New bug in classic Outlook can only be fixed via Microsoft support — www.bleepingcomputer.com — 01.10.2025 21:43