A collaboration system manages a plurality of content objects that are shared by multiple users at corresponding user devices in corresponding computing environments. Policies that govern interactions over the plurality of content objects are established. A content object upload request from a first user belonging to a first enterprise is processed by the collaboration system and then the content object is shared with a second user of a second enterprise. Security characteristics pertaining to the second user, and/or the second enterprise, and/or the second user's devices are initially unknown or unverified. As such, upon receiving interaction events raised by a user device of the second user, a set of interaction attributes associated with the interaction events are gathered. One or more trust policies are applied to the interaction attributes to evaluate security conditions that correspond to the interaction events. A response is generated based on the evaluated security conditions.