The best way with Unity Connection is with the use of this excellent tool from
the great suite of Unity Tools (use the ** reset" feature **).
Unity Connection Bulk User Delete
For resetting users you have the option of emptying the mailbox, resetting greetings, deleting voice names, resetting passwords, removing private lists and a number of other options you may choose. For installations where the user base “changes over” frequently such as schools this may be a nicer option. This option is also allowed for CoRes installations since it does not involve the removal of user objects from the Connection database.