Below are the steps you can go through to troubleshoot your email search issue in Outlook for Exchange:

1. Check if search is correctly enabled in Outlook.
2. Make sure that Windows Desktop Search is installed and updated.
3. Verify if specific add-ins are enabled and updated.
4. Verify if your Outlook is connected to the Exchange server.
5. Check the Outlook Search service.
6. Try to manually reindex the mail account.