diff --git a/lib/Config/Database.php b/lib/Config/Database.php
index ca7c5f4c6b..23c7e59be7 100644
--- a/lib/Config/Database.php
+++ b/lib/Config/Database.php
@@ -70,6 +70,7 @@ class Database {
       $subscriber_custom_field = Env::$db_prefix . 'subscriber_custom_field';
       $newsletter_segment = Env::$db_prefix . 'newsletter_segment';
       $scheduled_tasks = Env::$db_prefix . 'scheduled_tasks';
+      $scheduled_task_subscribers = Env::$db_prefix . 'scheduled_task_subscribers';
       $sending_queues = Env::$db_prefix . 'sending_queues';
       $newsletters = Env::$db_prefix . 'newsletters';
       $newsletter_templates = Env::$db_prefix . 'newsletter_templates';
@@ -92,6 +93,7 @@ class Database {
       define('MP_SUBSCRIBER_SEGMENT_TABLE', $subscriber_segment);
       define('MP_SUBSCRIBER_CUSTOM_FIELD_TABLE', $subscriber_custom_field);
       define('MP_SCHEDULED_TASKS_TABLE', $scheduled_tasks);
+      define('MP_SCHEDULED_TASK_SUBSCRIBERS_TABLE', $scheduled_task_subscribers);
       define('MP_SENDING_QUEUES_TABLE', $sending_queues);
       define('MP_NEWSLETTERS_TABLE', $newsletters);
       define('MP_NEWSLETTER_TEMPLATES_TABLE', $newsletter_templates);
diff --git a/lib/Config/Migrator.php b/lib/Config/Migrator.php
index 841626c710..7707a7e3aa 100644
--- a/lib/Config/Migrator.php
+++ b/lib/Config/Migrator.php
@@ -18,6 +18,7 @@ class Migrator {
       'settings',
       'custom_fields',
       'scheduled_tasks',
+      'scheduled_task_subscribers',
       'sending_queues',
       'subscribers',
       'subscriber_segment',
@@ -109,12 +110,8 @@ class Migrator {
     $attributes = array(
       'id mediumint(9) NOT NULL AUTO_INCREMENT,',
       'type varchar(90) NULL DEFAULT NULL,',
-      'subscribers longtext,',
       'status varchar(12) NULL DEFAULT NULL,',
       'priority mediumint(9) NOT NULL DEFAULT 0,',
-      'count_total mediumint(9) NOT NULL DEFAULT 0,',
-      'count_processed mediumint(9) NOT NULL DEFAULT 0,',
-      'count_to_process mediumint(9) NOT NULL DEFAULT 0,',
       'scheduled_at TIMESTAMP NULL,',
       'processed_at TIMESTAMP NULL,',
       'created_at TIMESTAMP NULL,',
@@ -125,6 +122,17 @@ class Migrator {
     return $this->sqlify(__FUNCTION__, $attributes);
   }
 
+  function scheduledTaskSubscribers() {
+    $attributes = array(
+      'task_id mediumint(9) NOT NULL,',
+      'subscriber_id mediumint(9) NOT NULL,',
+      'processed int(1) NULL,',
+      'created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,',
+      'PRIMARY KEY  (task_id, subscriber_id)',
+    );
+    return $this->sqlify(__FUNCTION__, $attributes);
+  }
+
   function sendingQueues() {
     $attributes = array(
       'id mediumint(9) NOT NULL AUTO_INCREMENT,',
diff --git a/lib/Cron/Workers/Bounce.php b/lib/Cron/Workers/Bounce.php
index 10ef580f56..537d79e963 100644
--- a/lib/Cron/Workers/Bounce.php
+++ b/lib/Cron/Workers/Bounce.php
@@ -4,6 +4,8 @@ namespace MailPoet\Cron\Workers;
 use MailPoet\Cron\CronHelper;
 use MailPoet\Mailer\Mailer;
 use MailPoet\Models\ScheduledTask;
+use MailPoet\Models\ScheduledTaskSubscriber;
+use MailPoet\Tasks\Subscribers\BatchIterator;
 use MailPoet\Models\Subscriber;
 use MailPoet\Services\Bridge;
 use MailPoet\Services\Bridge\API;
@@ -48,28 +50,19 @@ class Bounce extends SimpleWorker {
     }
 
     // update current task
-    $task->subscribers = serialize(
-      array(
-        'to_process' => $subscribers
-      )
-    );
-    $task->count_total = $task->count_to_process = count($subscribers);
+    ScheduledTaskSubscriber::addSubscribers($task->id, $subscribers);
 
     return parent::prepareTask($task);
   }
 
   function processTask(ScheduledTask $task) {
-    $task->subscribers = $task->getSubscribers();
-    if(empty($task->subscribers['to_process'])) {
+    $subscriber_batches = new BatchIterator($task->id, self::BATCH_SIZE);
+
+    if(count($subscriber_batches) === 0) {
       $task->delete();
       return false;
     }
 
-    $subscriber_batches = array_chunk(
-      $task->subscribers['to_process'],
-      self::BATCH_SIZE
-    );
-
     foreach($subscriber_batches as $subscribers_to_process_ids) {
       // abort if execution limit is reached
       CronHelper::enforceExecutionLimit($this->timer);
diff --git a/lib/Models/ScheduledTask.php b/lib/Models/ScheduledTask.php
index 9edb31e688..a8bb61afa0 100644
--- a/lib/Models/ScheduledTask.php
+++ b/lib/Models/ScheduledTask.php
@@ -11,6 +11,10 @@ class ScheduledTask extends Model {
   const PRIORITY_MEDIUM = 5;
   const PRIORITY_LOW = 10;
 
+  function taskSubscribers() {
+    return $this->has_many(__NAMESPACE__ . '\ScheduledTaskSubscriber', 'task_id', 'id');
+  }
+
   function complete() {
     $this->set('status', self::STATUS_COMPLETED);
     $this->save();
@@ -18,79 +22,28 @@ class ScheduledTask extends Model {
   }
 
   function save() {
-    if(!is_serialized($this->subscribers)) {
-      $this->set('subscribers', serialize($this->subscribers));
-    }
     // set the default priority to medium
     if(!$this->priority) {
       $this->priority = self::PRIORITY_MEDIUM;
     }
     parent::save();
-    $this->subscribers = $this->getSubscribers();
     return $this;
   }
 
-  function getSubscribers() {
-    if(!is_serialized($this->subscribers)) {
-      return $this->subscribers;
-    }
-    $subscribers = unserialize($this->subscribers);
-    if(empty($subscribers['processed'])) {
-      $subscribers['processed'] = array();
-    }
-    return $subscribers;
+  function updateProcessedSubscribers(array $processed_subscribers) {
+    $this->taskSubscribers()
+      ->whereIn('subscriber_id', $processed_subscribers)
+      ->findResultSet()
+      ->set('processed', ScheduledTaskSubscriber::STATUS_PROCESSED)
+      ->save();
+    $this->checkCompleted();
   }
 
-  function isSubscriberProcessed($subscriber_id) {
-    $subscribers = $this->getSubscribers();
-    return in_array($subscriber_id, $subscribers['processed']);
-  }
-
-  function asArray() {
-    $model = parent::asArray();
-    $model['subscribers'] = (is_serialized($this->subscribers))
-      ? unserialize($this->subscribers)
-      : $this->subscribers;
-    return $model;
-  }
-
-  function removeNonexistentSubscribers($subscribers_to_remove) {
-    $subscribers = $this->getSubscribers();
-    $subscribers['to_process'] = array_values(
-      array_diff(
-        $subscribers['to_process'],
-        $subscribers_to_remove
-      )
-    );
-    $this->subscribers = $subscribers;
-    $this->updateCount();
-  }
-
-  function updateProcessedSubscribers($processed_subscribers) {
-    $subscribers = $this->getSubscribers();
-    $subscribers['processed'] = array_merge(
-      $subscribers['processed'],
-      $processed_subscribers
-    );
-    $subscribers['to_process'] = array_values(
-      array_diff(
-        $subscribers['to_process'],
-        $processed_subscribers
-      )
-    );
-    $this->subscribers = $subscribers;
-    $this->updateCount();
-  }
-
-  function updateCount() {
-    $this->subscribers = $this->getSubscribers();
-    $this->count_processed = count($this->subscribers['processed']);
-    $this->count_to_process = count($this->subscribers['to_process']);
-    $this->count_total = $this->count_processed + $this->count_to_process;
-    if(!$this->count_to_process) {
+  private function checkCompleted() {
+    if(!ScheduledTaskSubscriber::getToProcessCount($this->id)) {
       $this->processed_at = current_time('mysql');
       $this->status = self::STATUS_COMPLETED;
+      return $this->save();
     }
-    return $this->save();
   }
-}
\ No newline at end of file
+}
diff --git a/lib/Models/ScheduledTaskSubscriber.php b/lib/Models/ScheduledTaskSubscriber.php
new file mode 100644
index 0000000000..c0a9debb89
--- /dev/null
+++ b/lib/Models/ScheduledTaskSubscriber.php
@@ -0,0 +1,61 @@
+<?php
+namespace MailPoet\Models;
+
+if(!defined('ABSPATH')) exit;
+
+class ScheduledTaskSubscriber extends Model {
+  const STATUS_TO_PROCESS = 0;
+  const STATUS_PROCESSED = 1;
+
+  public static $_table = MP_SCHEDULED_TASK_SUBSCRIBERS_TABLE;
+  public static $_id_column = array('task_id', 'subscriber_id');
+
+  static function createOrUpdate($data = array()) {
+    if(!is_array($data) || empty($data['task_id']) || empty($data['subscriber_id'])) return;
+
+    $task_subscriber = self::where('subscriber_id', $data['subscriber_id'])
+      ->where('task_id', $data['task_id'])
+      ->findOne();
+
+    if(empty($task_subscriber)) $task_subscriber = self::create();
+
+    $task_subscriber->task_id = $data['task_id'];
+    $task_subscriber->subscriber_id = $data['subscriber_id'];
+    $task_subscriber->processed = self::STATUS_TO_PROCESS;
+    $task_subscriber->save();
+
+    return $task_subscriber;
+  }
+
+  static function addSubscribers($task_id, array $subscriber_ids) {
+    foreach($subscriber_ids as $subscriber_id) {
+      self::createOrUpdate(array(
+        'task_id' => $task_id,
+        'subscriber_id' => $subscriber_id
+      ));
+    }
+  }
+
+  static function getToProcessCount($task_id) {
+    return self::getCount($task_id, false);
+  }
+
+  static function getProcessedCount($task_id) {
+    return self::getCount($task_id, true);
+  }
+
+  static function getTotalCount($task_id) {
+    return self::getCount($task_id);
+  }
+
+  private static function getCount($task_id, $processed = null) {
+    $orm = self::where('task_id', $task_id);
+    if(!is_null($processed)) {
+      $orm->where(
+        'processed',
+        ($processed) ? self::STATUS_PROCESSED : self::STATUS_TO_PROCESS
+      );
+    }
+    return $orm->count();
+  }
+}
diff --git a/lib/Tasks/Subscribers/BatchIterator.php b/lib/Tasks/Subscribers/BatchIterator.php
new file mode 100644
index 0000000000..f1102bfc7f
--- /dev/null
+++ b/lib/Tasks/Subscribers/BatchIterator.php
@@ -0,0 +1,59 @@
+<?php
+namespace MailPoet\Tasks\Subscribers;
+
+use MailPoet\Models\ScheduledTaskSubscriber;
+use MailPoet\Util\Helpers;
+
+if(!defined('ABSPATH')) exit;
+
+class BatchIterator implements \Iterator, \Countable {
+  private $task_id;
+  private $batch_size;
+  private $offset = 0;
+
+  function __construct($task_id, $batch_size) {
+    if($task_id <= 0) {
+      throw new \Exception('Task ID must be greater than zero');
+    } elseif($batch_size <= 0) {
+      throw new \Exception('Batch size must be greater than zero');
+    }
+    $this->task_id = (int)$task_id;
+    $this->batch_size = (int)$batch_size;
+  }
+
+  function rewind() {
+    $this->offset = 0;
+  }
+
+  function current() {
+    $subscribers = $this->getSubscribers()
+      ->orderByAsc('subscriber_id')
+      ->limit($this->batch_size)
+      ->offset($this->offset)
+      ->findArray();
+    $subscribers = Helpers::arrayColumn($subscribers, 'subscriber_id');
+    return $subscribers;
+  }
+
+  function key() {
+    return $this->offset;
+  }
+
+  function next() {
+    $this->offset += $this->batch_size;
+  }
+
+  function valid() {
+    return $this->offset < $this->count();
+  }
+
+  function count() {
+    return $this->getSubscribers()->count();
+  }
+
+  private function getSubscribers() {
+    return ScheduledTaskSubscriber::select('subscriber_id')
+      ->where('task_id', $this->task_id)
+      ->where('processed', ScheduledTaskSubscriber::STATUS_TO_PROCESS);
+  }
+}
diff --git a/tests/_bootstrap.php b/tests/_bootstrap.php
index 85e9ec5b1b..7a8ad81072 100644
--- a/tests/_bootstrap.php
+++ b/tests/_bootstrap.php
@@ -19,6 +19,7 @@ $models = array(
   'NewsletterOptionField',
   'Segment',
   'ScheduledTask',
+  'ScheduledTaskSubscriber',
   'SendingQueue',
   'Setting',
   'Subscriber',
diff --git a/tests/unit/Cron/Workers/BounceTest.php b/tests/unit/Cron/Workers/BounceTest.php
index 0da973c21d..f87a24ab91 100644
--- a/tests/unit/Cron/Workers/BounceTest.php
+++ b/tests/unit/Cron/Workers/BounceTest.php
@@ -4,6 +4,7 @@ use Carbon\Carbon;
 use MailPoet\Cron\Workers\Bounce;
 use MailPoet\Mailer\Mailer;
 use MailPoet\Models\ScheduledTask;
+use MailPoet\Models\ScheduledTaskSubscriber;
 use MailPoet\Models\Setting;
 use MailPoet\Models\Subscriber;
 use MailPoet\Services\Bridge\API;
@@ -58,10 +59,10 @@ class BounceTest extends MailPoetTest {
 
   function testItPreparesTask() {
     $task = $this->createScheduledTask();
-    expect(empty($task->subscribers['to_process']))->true();
+    expect(ScheduledTaskSubscriber::getToProcessCount($task->id))->isEmpty();
     $this->worker->prepareTask($task);
     expect($task->status)->null();
-    expect(!empty($task->subscribers['to_process']))->true();
+    expect(ScheduledTaskSubscriber::getToProcessCount($task->id))->notEmpty();
   }
 
   function testItDeletesTaskIfThereAreNoSubscribersToProcessWhenProcessingTask() {
@@ -76,9 +77,9 @@ class BounceTest extends MailPoetTest {
   function testItProcessesTask() {
     $task = $this->createRunningTask();
     $this->worker->prepareTask($task);
-    expect(!empty($task->subscribers['to_process']))->true();
+    expect(ScheduledTaskSubscriber::getToProcessCount($task->id))->notEmpty();
     $this->worker->processTask($task);
-    expect(!empty($task->subscribers['processed']))->true();
+    expect(ScheduledTaskSubscriber::getProcessedCount($task->id))->notEmpty();
   }
 
   function testItSetsSubscriberStatusAsBounced() {
@@ -125,6 +126,7 @@ class BounceTest extends MailPoetTest {
   function _after() {
     ORM::raw_execute('TRUNCATE ' . Setting::$_table);
     ORM::raw_execute('TRUNCATE ' . ScheduledTask::$_table);
+    ORM::raw_execute('TRUNCATE ' . ScheduledTaskSubscriber::$_table);
     ORM::raw_execute('TRUNCATE ' . Subscriber::$_table);
   }
 }
\ No newline at end of file