Disclaimer, I have not ever used this application. Im practically assuming after looking at the application code.
Also I know a bit about Exchange... you'd need permission to read their mailboxes first. Sure any admin can do this, but I seriously doubt (for that reason along) that they built the functionality into the splunk app. Because most users don't care to read other's emails... but also they want their app to work without full access, special permissions, etc. So if you imagine half of the dashboards working but the others don't work until you get an admin service account for exchange setup in the app.... why even include the advanced stuff at that point? You'd probably be better off making 2 apps, one lets you spy on peoples email, and the other lets you monitor exchange for performance issues, etc.