diff --git a/pub/fed.go b/pub/fed.go
index d16736c..02df564 100644
--- a/pub/fed.go
+++ b/pub/fed.go
@@ -66,7 +66,7 @@ func NewSocialPubber(clock Clock, app Application, socialApp SocialApp, cb Callb
 // servers. All are required unless explicitly stated otherwise.
 type DeliveryOptions struct {
 	// Client to use when sending http requests to federating peers.
-	Client *http.Client
+	Client HttpClient
 	// Agent string to send in http requests.
 	Agent string
 	// Maximum unnesting done when determining who to send messages to. Must
@@ -110,7 +110,7 @@ func NewFederatingPubber(clock Clock, app Application, fApp FederateApp, cb Call
 
 // NewPubber provides a Pubber that implements both the Social API and the
 // Federating API in ActivityPub.
-func NewPubber(clock Clock, app Application, sApp SocialApp, fApp FederateApp, server, client Callbacker, d DeliveryOptions) Pubber {
+func NewPubber(clock Clock, app Application, sApp SocialApp, fApp FederateApp, client, server Callbacker, d DeliveryOptions) Pubber {
 	return &federator{
 		Clock:            clock,
 		App:              app,
@@ -151,7 +151,7 @@ type federator struct {
 	// Client is used to federate with other ActivityPub servers.
 	//
 	// It is only required if EnableServer is true.
-	Client *http.Client
+	Client HttpClient
 	// Agent is the User-Agent string to use in HTTP headers when
 	// federating with another server. It will automatically be appended
 	// with '(go-fed ActivityPub)'.
diff --git a/pub/interfaces.go b/pub/interfaces.go
index 3e573b1..90bff18 100644
--- a/pub/interfaces.go
+++ b/pub/interfaces.go
@@ -25,6 +25,11 @@ type Clock interface {
 	Now() time.Time
 }
 
+// HttpClient sends http requests.
+type HttpClient interface {
+	Do(req *http.Request) (*http.Response, error)
+}
+
 // Application is provided by users of this library in order to implement a
 // social-federative-web application.
 //
@@ -184,6 +189,13 @@ type typeIder interface {
 	Serialize() (m map[string]interface{}, e error)
 }
 
+// actor is an object that is an ActivityPub Actor. The specification is more
+// strict than what we include here, only for our internal use.
+type actor interface {
+	HasInbox() (ok bool)
+	GetInbox() (v url.URL)
+}
+
 // actorObject is an object that has "actor" or "attributedTo" properties,
 // representing the author or originator of the object.
 type actorObject interface {
diff --git a/pub/internal.go b/pub/internal.go
index 4acf2c3..5f03bc0 100644
--- a/pub/internal.go
+++ b/pub/internal.go
@@ -63,7 +63,7 @@ func isPublic(s string) bool {
 
 // dereference makes an HTTP GET request to an IRI in order to obtain the
 // ActivityStream representation.
-func dereference(c *http.Client, u url.URL, agent string) ([]byte, error) {
+func dereference(c HttpClient, u url.URL, agent string) ([]byte, error) {
 	// TODO: (section 7.1) The server MUST dereference the collection (with the user's credentials)
 	req, err := http.NewRequest("GET", u.String(), nil)
 	if err != nil {
@@ -86,7 +86,7 @@ func dereference(c *http.Client, u url.URL, agent string) ([]byte, error) {
 
 // postToOutbox will attempt to send a POST request to the given URL with the
 // body set to the provided bytes.
-func postToOutbox(c *http.Client, b []byte, to url.URL, agent string) error {
+func postToOutbox(c HttpClient, b []byte, to url.URL, agent string) error {
 	byteCopy := make([]byte, 0, len(b))
 	copy(b, byteCopy)
 	buf := bytes.NewBuffer(byteCopy)
@@ -234,11 +234,11 @@ func (c *federator) prepare(o deliverableObject) ([]url.URL, error) {
 // resolveInboxes takes a list of Actor id URIs and returns them as concrete
 // instances of actorObject. It applies recursively when it encounters a target
 // that is a Collection or OrderedCollection.
-func (c *federator) resolveInboxes(r []url.URL, depth int, max int) ([]actorObject, error) {
+func (c *federator) resolveInboxes(r []url.URL, depth int, max int) ([]actor, error) {
 	if depth >= max {
 		return nil, nil
 	}
-	a := make([]actorObject, 0, len(r))
+	a := make([]actor, 0, len(r))
 	for _, u := range r {
 		// Do not retry here -- if a dereference fails, then fail the
 		// entire delivery.
@@ -250,7 +250,7 @@ func (c *federator) resolveInboxes(r []url.URL, depth int, max int) ([]actorObje
 		if err = json.Unmarshal(resp, &m); err != nil {
 			return nil, err
 		}
-		var actor actorObject
+		var actor actor
 		var co *streams.Collection
 		var oc *streams.OrderedCollection
 		var cp *streams.CollectionPage
@@ -314,7 +314,7 @@ func (c *federator) resolveInboxes(r []url.URL, depth int, max int) ([]actorObje
 }
 
 // getInboxes extracts the 'inbox' IRIs from actors.
-func getInboxes(a []actorObject) []url.URL {
+func getInboxes(a []actor) []url.URL {
 	var u []url.URL
 	for _, actor := range a {
 		if actor.HasInbox() {
@@ -393,9 +393,10 @@ func dedupeIRIs(recipients, ignored []url.URL) (out []url.URL) {
 		ignoredMap[elem] = true
 	}
 	outMap := make(map[url.URL]bool, len(recipients))
-	for k, _ := range outMap {
-		if !ignoredMap[k] {
+	for _, k := range recipients {
+		if !ignoredMap[k] && !outMap[k] {
 			out = append(out, k)
+			outMap[k] = true
 		}
 	}
 	return
@@ -559,7 +560,7 @@ func getAudienceIRIs(o deliverableObject) []url.URL {
 
 // doForCollectionPage applies a function over a collection and its subsequent
 // pages recursively. It returns the first non-nil error it encounters.
-func doForCollectionPage(h *http.Client, agent string, cb func(c vocab.CollectionPageType) error, c vocab.CollectionPageType) error {
+func doForCollectionPage(h HttpClient, agent string, cb func(c vocab.CollectionPageType) error, c vocab.CollectionPageType) error {
 	err := cb(c)
 	if err != nil {
 		return err
@@ -614,7 +615,7 @@ func doForCollectionPage(h *http.Client, agent string, cb func(c vocab.Collectio
 // doForOrderedCollectionPage applies a function over a collection and its
 // subsequent pages recursively. It returns the first non-nil error it
 // encounters.
-func doForOrderedCollectionPage(h *http.Client, agent string, cb func(c vocab.OrderedCollectionPageType) error, c vocab.OrderedCollectionPageType) error {
+func doForOrderedCollectionPage(h HttpClient, agent string, cb func(c vocab.OrderedCollectionPageType) error, c vocab.OrderedCollectionPageType) error {
 	err := cb(c)
 	if err != nil {
 		return err
diff --git a/pub/resolvers.go b/pub/resolvers.go
index 7616c0c..85d778b 100644
--- a/pub/resolvers.go
+++ b/pub/resolvers.go
@@ -37,11 +37,11 @@ func ToPubObject(m map[string]interface{}) (t []PubObject, e error) {
 
 func getActorObject(m map[string]interface{}) (actorObject, error) {
 	var a actorObject
-	err := toActorResolver(&a).Deserialize(m)
+	err := toActorObjectResolver(&a).Deserialize(m)
 	return a, err
 }
 
-func toActorResolver(a *actorObject) *streams.Resolver {
+func toActorObjectResolver(a *actorObject) *streams.Resolver {
 	return &streams.Resolver{
 		AnyObjectCallback: func(i vocab.ObjectType) error {
 			if o, ok := i.(actorObject); ok {
@@ -52,7 +52,18 @@ func toActorResolver(a *actorObject) *streams.Resolver {
 	}
 }
 
-func toActorCollectionResolver(a *actorObject, c **streams.Collection, oc **streams.OrderedCollection, cp **streams.CollectionPage, ocp **streams.OrderedCollectionPage) *streams.Resolver {
+func toActorResolver(a *actor) *streams.Resolver {
+	return &streams.Resolver{
+		AnyObjectCallback: func(i vocab.ObjectType) error {
+			if o, ok := i.(actor); ok {
+				*a = o
+			}
+			return nil
+		},
+	}
+}
+
+func toActorCollectionResolver(a *actor, c **streams.Collection, oc **streams.OrderedCollection, cp **streams.CollectionPage, ocp **streams.OrderedCollectionPage) *streams.Resolver {
 	r := toActorResolver(a)
 	r.CollectionCallback = func(i *streams.Collection) error {
 		*c = i