I'm working on an application which needs to retrieve information of different users (inbox). I'd like to know if this is possible with a granted user (ie: admin).
For example I've worked with other social networks that allow an admin user to retrieve private messages of other users, or another option would be to retrieve access tokens of different users by making a call from an administrator.
Check out Core V3 API - Run-As Feature & Signed Add-Ons for a way to perform API requests as if you were a specific user (which includes the inbox requests). Requires full Jive Admin account permissions on your own account for this to work.