diff --git a/actions/apactoroutbox.php b/actions/apactoroutbox.php
index b357cd2..bf8c15e 100644
--- a/actions/apactoroutbox.php
+++ b/actions/apactoroutbox.php
@@ -124,7 +124,7 @@ class apActorOutboxAction extends ManagedAction
             // TODO: Handle other types
             if ($note->object_type == 'http://activitystrea.ms/schema/1.0/note') {
                 $notices[] = Activitypub_create::create_to_array(
-                    ActivityPubPlugin::actor_uri($note->getProfile()), 
+                    ActivityPubPlugin::actor_uri($note->getProfile()),
                     Activitypub_notice::notice_to_array($note)
                 );
             }
diff --git a/actions/apinbox.php b/actions/apinbox.php
index 2844c38..991ff54 100755
--- a/actions/apinbox.php
+++ b/actions/apinbox.php
@@ -60,11 +60,45 @@ class apInboxAction extends ManagedAction
         common_debug('ActivityPub Inbox: Request contents: '.$data);
         $data = json_decode(file_get_contents('php://input'), true);
 
+        if (!isset($data['actor'])) {
+            ActivityPubReturn::error('Actor not found in the request.');
+        }
+
+        $actor = ActivityPub_explorer::get_profile_from_url($data['actor']);
+        $actor_public_key = new Activitypub_rsa();
+        $actor_public_key = $actor_public_key->ensure_public_key($actor);
+
+        common_debug('ActivityPub Inbox: HTTP Signature: Validation will now start!');
+
+        $headers = $this->get_all_headers();
+        common_debug('ActivityPub Inbox: Request Headers: '.print_r($headers, true));
+
+        // TODO: Validate HTTP Signature
+
+        common_debug('ActivityPub Inbox: HTTP Signature: Authorized request. Will now start the inbox handler.');
+
         try {
-            new Activitypub_inbox_handler($data);
+            new Activitypub_inbox_handler($data, $actor);
             ActivityPubReturn::answer();
         } catch (Exception $e) {
             ActivityPubReturn::error($e->getMessage());
         }
     }
+
+    /**
+     * Get all HTTP header key/values as an associative array for the current request.
+     *
+     * @author PHP Manual Contributed Notes <joyview@gmail.com>
+     * @return string[string] The HTTP header key/value pairs.
+     */
+    private function get_all_headers()
+    {
+        $headers = [];
+        foreach ($_SERVER as $name => $value) {
+            if (substr($name, 0, 5) == 'HTTP_') {
+                $headers[strtolower(str_replace(' ', '-', ucwords(strtolower(str_replace('_', ' ', substr($name, 5))))))] = $value;
+            }
+        }
+        return $headers;
+    }
 }
diff --git a/classes/Activitypub_notice.php b/classes/Activitypub_notice.php
index c98bb5d..2f413a5 100755
--- a/classes/Activitypub_notice.php
+++ b/classes/Activitypub_notice.php
@@ -202,7 +202,7 @@ class Activitypub_notice extends Managed_DataObject
 
         // Mentions
         $mentions = [];
-        if (isset ($object['tag']) && is_array($object['tag'])) {
+        if (isset($object['tag']) && is_array($object['tag'])) {
             foreach ($object['tag'] as $tag) {
                 if ($tag['type'] == 'Mention') {
                     $mentions[] = $tag['href'];
diff --git a/utils/inbox_handler.php b/utils/inbox_handler.php
index 3f78a77..c0680dc 100644
--- a/utils/inbox_handler.php
+++ b/utils/inbox_handler.php
@@ -49,8 +49,9 @@ class Activitypub_inbox_handler
      *
      * @author Diogo Cordeiro <diogo@fc.up.pt>
      * @param Array $activity Activity we are receiving
+     * @param Profile $actor_profile Actor originating the activity
      */
-    public function __construct($activity)
+    public function __construct($activity, $actor_profile = null)
     {
         $this->activity = $activity;
         $this->object = $activity['object'];
@@ -59,7 +60,11 @@ class Activitypub_inbox_handler
         $this->validate_activity();
 
         // Get Actor's Profile
-        $this->actor = ActivityPub_explorer::get_profile_from_url($this->activity['actor']);
+        if (!is_null($actor_profile)) {
+            $this->actor = $actor_profile;
+        } else {
+            $this->actor = ActivityPub_explorer::get_profile_from_url($this->activity['actor']);
+        }
 
         // Handle the Activity
         $this->process();
diff --git a/utils/postman.php b/utils/postman.php
index e608d05..03f6509 100755
--- a/utils/postman.php
+++ b/utils/postman.php
@@ -63,15 +63,22 @@ class Activitypub_postman
     public function __construct($from, $to = [])
     {
         $this->actor = $from;
-        $this->to = $to;
-        $this->to[]= common_local_url('apActorFollowers', ['id' => $from->getID()]);
+        $discovery = new Activitypub_explorer();
+        $this->to = array_merge(
+                $to,
+                $discovery->lookup(common_local_url(
+                    'apActorFollowers',
+                    ['id' => $from->getID()]
+                ))
+        );
+        unset($discovery);
         $this->actor_uri = ActivityPubPlugin::actor_uri($this->actor);
 
         $actor_private_key = new Activitypub_rsa();
         $actor_private_key = $actor_private_key->get_private_key($this->actor);
 
         $context = new Context([
-            'keys' => [$this->actor_uri."#public-key" => $actor_private_key],
+            'keys' => [$this->actor_uri.'#public-key' => $actor_private_key],
             'algorithm' => 'rsa-sha256',
             'headers' => ['(request-target)', 'date', 'content-type', 'accept', 'user-agent'],
         ]);