Admins in your account have the option to set visibility permissions on each of your mailboxes in Groove. This allows you to only give certain users or groups of users access to the conversations in those mailboxes.
You'll find these options down at the bottom of each individual mailbox settings page if you go into your account Settings > Conversations > Mailboxes.
There is a section near the bottom of that page that says "Who can see this?" with a dropdown menu next to it.
Here you can select between Everyone, Only Me, Select Users, and Select Groups. The default will always be Everyone, but should you need to change that, make the appropriate selections and Save.