To invite an Outlook contact to your MangoApps domain, you first need to enable Outlook plug in from MangoApps for desktop preferences.
Make sure to enable “Get colleagues and other contacts from Outlook”
Then go to MangoApps for Desktop and navigate to “Colleagues and teams” tab
Click the more button to choose “Invite Colleagues”
Place check marks in all the colleagues that you want to invite to MangoApps, edit the personal message if necessary, then click “Send Invites”.