Portal Groups are used to enable Group Administrators to view and manage email assigned to their group. Note that Group features are not viewable if the installed license does not support the Portal server.
The Default Group is always present within the system and cannot be removed. To add an additional Group:
Menu > Portal > Portal Groups > Actions > Add
To change the assignment of a Domain group:
Menu > Configuration > Domains > Edit > Group
All domain email will be viewable by any Group Administrator assigned to that group.