To search for card content, you can use the kind:microsoftteams or itemclass:IPM.SkypeTeams.Message search conditions. When reviewing search results, card content generated by bots in a Teams channel has the Sender/Author email property as @teams.microsoft.com, where appname is the name of the app that generated the card content. If card content was generated by a user, the value of Sender/Author identifies the user.