diff --git a/lib/Cron/CronHelper.php b/lib/Cron/CronHelper.php
index 36b7c7aad6..f2286a84ec 100644
--- a/lib/Cron/CronHelper.php
+++ b/lib/Cron/CronHelper.php
@@ -7,8 +7,9 @@ use MailPoet\Util\Security;
 if(!defined('ABSPATH')) exit;
 
 class CronHelper {
-  static $daemon_execution_limit = 20;
-  static $daemon_execution_timeout = 35;
+  const daemon_execution_limit = 20;
+  const daemon_execution_timeout = 35;
+  const daemon_request_timeout = 2;
 
   static function createDaemon($token) {
     $daemon = array(
@@ -36,7 +37,7 @@ class CronHelper {
     return Security::generateRandomString();
   }
 
-  static function accessDaemon($token, $timeout = 2) {
+  static function accessDaemon($token, $timeout = self::daemon_request_timeout) {
     $payload = serialize(array('token' => $token));
     $url = '/?mailpoet-api&section=queue&action=run&request_payload=' .
       base64_encode($payload);
diff --git a/lib/Cron/Daemon.php b/lib/Cron/Daemon.php
index 9d6faf69b2..c085804984 100644
--- a/lib/Cron/Daemon.php
+++ b/lib/Cron/Daemon.php
@@ -11,7 +11,7 @@ class Daemon {
   public $daemon;
   public $request_payload;
   public $refreshed_token;
-  private $daemon_request_timeout = 3;
+  const daemon_request_timeout = 5;
   private $timer;
 
   function __construct($request_payload = array()) {
@@ -40,8 +40,8 @@ class Daemon {
     } catch(Exception $e) {
     }
     $elapsed_time = microtime(true) - $this->timer;
-    if($elapsed_time < CronHelper::$daemon_execution_limit) {
-      sleep(CronHelper::$daemon_execution_limit - $elapsed_time);
+    if($elapsed_time < CronHelper::daemon_execution_limit) {
+      sleep(CronHelper::daemon_execution_limit - $elapsed_time);
     }
     // after each execution, re-read daemon data in case it was deleted or
     // its status has changed
@@ -73,7 +73,7 @@ class Daemon {
   }
 
   function callSelf() {
-    CronHelper::accessDaemon($this->token, $this->daemon_request_timeout);
+    CronHelper::accessDaemon($this->token, self::daemon_request_timeout);
     exit;
   }
 }
\ No newline at end of file
diff --git a/lib/Cron/Supervisor.php b/lib/Cron/Supervisor.php
index 6a5476ddc3..848b3167a0 100644
--- a/lib/Cron/Supervisor.php
+++ b/lib/Cron/Supervisor.php
@@ -31,13 +31,13 @@ class Supervisor {
     $elapsed_time = time() - (int) $daemon['updated_at'];
     // if it's been less than 40 seconds since last execution and we're not
     // force-running the daemon, return its status and do nothing
-    if($elapsed_time < CronHelper::$daemon_execution_timeout && !$this->force_run) {
+    if($elapsed_time < CronHelper::daemon_execution_timeout && !$this->force_run) {
       return $this->formatDaemonStatusMessage($daemon['status']);
     }
     // if it's been less than 40 seconds since last execution, we are
     // force-running the daemon and it's either being started or stopped,
     // return its status and do nothing
-    elseif($elapsed_time < CronHelper::$daemon_execution_timeout &&
+    elseif($elapsed_time < CronHelper::daemon_execution_timeout &&
       $this->force_run &&
       in_array($daemon['status'], array(
         'stopping',
diff --git a/lib/Cron/Workers/SendingQueue.php b/lib/Cron/Workers/SendingQueue.php
index 9301ee8dde..e47638b220 100644
--- a/lib/Cron/Workers/SendingQueue.php
+++ b/lib/Cron/Workers/SendingQueue.php
@@ -16,11 +16,16 @@ if(!defined('ABSPATH')) exit;
 class SendingQueue {
   public $mailer_config;
   public $mailer_log;
+  public $processing_method;
   private $timer;
+  const batch_size = 50;
 
   function __construct($timer = false) {
     $this->mailer_config = $this->getMailerConfig();
     $this->mailer_log = $this->getMailerLog();
+    $this->processing_method = ($this->mailer_config['method'] === 'MailPoet') ?
+      'processBulkSubscribers' :
+      'processIndividualSubscriber';
     $this->timer = ($timer) ? $timer : microtime(true);
   }
 
@@ -40,17 +45,14 @@ class SendingQueue {
       $newsletter = $newsletter->asArray();
       $newsletter['body'] = $this->renderNewsletter($newsletter);
       $mailer = $this->configureMailer($newsletter);
-      foreach(array_chunk($queue->subscribers->to_process, 5) as
+      foreach(array_chunk($queue->subscribers->to_process, self::batch_size) as
               $subscribers_ids) {
         $subscribers = Subscriber::whereIn('id', $subscribers_ids)
           ->findArray();
-        $processing_method = ($this->mailer_config['method'] === 'MailPoet') ?
-          'processBulkSubscribers' :
-          'processIndividualSubscriber';
         $queue->subscribers = call_user_func_array(
           array(
             $this,
-            $processing_method
+            $this->processing_method
           ),
           array(
             $mailer,
@@ -59,6 +61,7 @@ class SendingQueue {
             $queue
           )
         );
+        die('aaaa');
       }
     }
   }
@@ -101,6 +104,7 @@ class SendingQueue {
     $this->updateQueue($queue);
     $this->checkSendingLimit();
     $this->checkExecutionTimer();
+    die('zzz');
     return $queue->subscribers;
   }
 
@@ -185,7 +189,7 @@ class SendingQueue {
 
   function checkExecutionTimer() {
     $elapsed_time = microtime(true) - $this->timer;
-    if($elapsed_time >= CronHelper::$daemon_execution_limit) {
+    if($elapsed_time >= CronHelper::daemon_execution_limit) {
       throw new \Exception(__('Maximum execution time reached.'));
     }
   }
@@ -217,7 +221,7 @@ class SendingQueue {
       $queue->processed_at = date('Y-m-d H:i:s');
       $queue->status = 'completed';
     }
-    $queue->subscribers = serialize($queue->subscribers);
+    $queue->subscribers = serialize((array) $queue->subscribers);
     $queue->save();
   }
 
@@ -227,6 +231,7 @@ class SendingQueue {
   }
 
   function checkSendingLimit() {
+    // TODO: enforce sending frequency
   }
 
   function getMailerConfig() {