Open again System Preferences > go to Spotlight > Click the Privacy tab.Rebuilding the Spotlight without command line: Open System Preferences > Spotlight > Click the Privacy tab. Make sure that your new SSD drive is NOT excluded from the Spotlight index.
However some users still are unable to search Outlook messages, even with fresh Mojave installations. According to this Microsoft Knowledge Base article, the search bug has been fixed in macOS Mojave 10.14.5.