Router works for POST requests.

lib/Config/Initializer.php

@@ -1,6 +1,7 @@
 <?php
 namespace MailPoet\Config;
 use MailPoet\Models;
+use MailPoet\Router;
 
 if(!defined('ABSPATH')) exit;
 
@@ -18,6 +19,7 @@ class Initializer {
     $this->setupRenderer();
     $this->setupLocalizer();
     $this->setupMenu();
+    $this->setupRouter();
   }
 
   function setupDB() {
@@ -54,4 +56,9 @@ class Initializer {
     );
     $menu->init();
   }
+
+  function setupRouter() {
+    $router = new Router\Router();
+    $router->init();
+  }
 }