Make sure you are connected to a stable internet connection. If so, try running the application in a different browser. Check for any available updates. Ensure that Outlook has necessary access like calendar, date and time, country, for it to function properly. Clear the cache from the browser and reinstall the application. Another fix for Outlook email search not working is to rebuild the index. Go to the menu and type task manager. Then restart the Outlook application.
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https://technicaltipsblogshelp.blogspot.com/2022/04/Outlook-search-not-working.html