I have implemented this class to fetch mailThreads from PipeDrive API…

…. The resource was not already present in the API client.

The following end-points has been implemented.

GET https://api.pipedrive.com/v1/mailbox/mailThreads?folder=inbox&start=0&limit=2&api_token=??
GET https://api.pipedrive.com/v1/mailbox/mailThreads/122?api_token=

src/Resources/Mailbox.php

@@ -31,4 +31,15 @@ public function mailThreads($folder, $options = [])
 
         return $this->request->get('mailThreads', $options);
     }
+
+    /**
+     * Get mail messages inside specified mail thread by ID.
+     *
+     * @param $id   Mail threads ID to find messages.
+	 * @return Response
+     */
+    public function mailMessages($id)
+    {
+        return $this->request->get('mailThreads/:id/mailMessages', compact('id'));
+    }
 }