UnfetchedRemoteActor
    instance InstanceId
    ident    Text
    since    UTCTime Maybe

    UniqueUnfetchedRemoteActor instance ident

UnlinkedDelivery
    recipient UnfetchedRemoteActorId
    activity  OutboxItemId
    running   Bool

    UniqueUnlinkedDelivery recipient activity

Delivery
    recipient RemoteActorId
    activity  OutboxItemId
    running   Bool

    UniqueDelivery recipient activity