When I do a system wide search in Spotlight it will find Emails that contain the key word that I searched for. I only use Apple Mail on my Mac running macOS High Sierra 10.13. I do have the Microsoft Office / Outlook app on my machine but have not used Outlook for email in about 2 years. When I double click an email, that was found in Spotlight, the Outlook app opens and an error msg appears "Outlook cannot open the file because it is not associated with the default identity". Of course it's not. I never downloaded that email from my IMAP server in to Outlook because I've been using Mail. So how do I change Spotlight to find and open an Apple Mail email in a search?