In the Lists area of the VPOP3 administration, you cannot administer groups at all. This is because a group is not really a list, but many people think of them as lists, so they are included in the Lists area for convenience.
All you can see in the Lists section is the list of users in the group. Groups can only contain local users.
There are two types of groups: built-in groups, and custom groups.
There are three built-in groups in all installations of VPOP3:
•Everyone - this usually contains all users, but you can remove a user from the Everyone list by editing the user, and going to the Permissions tab, then unchecking the Put user in Everyone list option
•Admins - this contains all users who are administrators. You cannot remove or add users from this group except by altering their Administrator status (by editing the user, and going to the General tab, and setting the Administrator option).
•No-one - this contains no-one. You cannot add users to this group. This group can be useful if you want to have some messages simply disappear. For instance, you could create a Mapping of a certain email address to No-one, to have messages addressed to that email address simply vanish.
Administrators can create custom groups on the Settings » Groups page. Groups define certain behaviour for a group of users. Each user can only be in one custom group at once (but they can be in as many Lists as you want)
To add or remove a user from a group, edit the user, and choose the group from the Group drop-down list on the General tab. You can remove a user from all groups, by selecting the <None> entry from the list.