Microsoft Outlook showing error “Search performance will be impacted because Outlook is not configured to be indexed with Windows Search service” when trying to perform a search in mailbox, contacts and so on. Follow the below steps to resolve this error.
Rebuild Outlook Search Index
Step 1: In Microsoft Outlook 365, click on the File tab.
Step 2: Click on Options > Search > Indexing Options > Advanced button.
Step 3: Go to the Troubleshooting section, click on the Rebuild option.
Disable Indexing on Drive
Step 1: Right-click C drive, choose Properties > General tab.
Step 2: Uncheck Allow files on this drive to have contents indexed in addition to the properties.
Step 3: Choose Apply changes to this drive only.
Run Outlook in Safe Mode
Run Outlook in safe mode by pressing Ctrl key and click Outlook shortcut at the start menu, or type
outlook.exe /resetnavpane in Run box.
Delete and Recreate Outlook Profile
Delete the Outlook profile at Control Panel > Mail then a create a new profile.