@silverpill You allow a missing outbox in your FEP although it's required by AP. I think inbox should also be optional. For S2S, if a server has a sharedInbox, the actor-specific inbox endpoint is not very useful. A shared inbox endpoint plus activity/object targeting properties is enough. For duck typing, an "Actor" is a thing that performs an Activity: it's the object (in an RDF sense) of some Activity `actor` relationship.