According to my research, there are many causes why the Outlook search function stops working, you could follow below troubleshooting steps to narrow down this issue:
- Check the Windows Search service to make sure it is running and the startup type is "Automatic (Delayed Startup)". Try restarting the service.
- Go to the Control Panel, check under Indexing Options to see if Outlook has been indexed, and try to rebuild the index.
Control Panel > Indexing Options > select Advanced > Click Rebuild: - Use the windows troubleshooting tools: Settings > Update & Security > Troubleshoot > Search & Indexing
- Recreate a new outlook profile to check if this issue continues.
- Update outlook to the latest version.
For more details: Troubleshooting Outlook search issues
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