1. A method for persistently maintaining and exposing one or more previous object hierarchies to which an object belongs, comprising: maintaining said previous object hierarchies for said object across one or more hierarchy destroying operations; generating a user interface object that allows a user to select one of said persistent hierarchies; and responsive to said user selecting one of said persistent hierarchies, displaying said selected persistent hierarchy with said object as a currently selected object within said selected persistent hierarchy. put in dependent claims for having the object as latest (most recently received message), and the object is the founding object of the thread