diff --git a/mailpoet/lib/API/JSON/v1/Newsletters.php b/mailpoet/lib/API/JSON/v1/Newsletters.php
index 52bf52f0d5..f150d1d654 100644
--- a/mailpoet/lib/API/JSON/v1/Newsletters.php
+++ b/mailpoet/lib/API/JSON/v1/Newsletters.php
@@ -22,6 +22,7 @@ use MailPoet\Newsletter\Preview\SendPreviewException;
 use MailPoet\Newsletter\Scheduler\PostNotificationScheduler;
 use MailPoet\Newsletter\Scheduler\Scheduler;
 use MailPoet\Newsletter\Url as NewsletterUrl;
+use MailPoet\Newsletter\Validator;
 use MailPoet\Settings\SettingsController;
 use MailPoet\Settings\TrackingConfig;
 use MailPoet\UnexpectedValueException;
@@ -79,6 +80,9 @@ class Newsletters extends APIEndpoint {
   /** @var TrackingConfig */
   private $trackingConfig;
 
+  /** @var Validator */
+  private $validator;
+
   /** @var Scheduler */
   private $scheduler;
 
@@ -97,7 +101,8 @@ class Newsletters extends APIEndpoint {
     NewsletterSaveController $newsletterSaveController,
     NewsletterUrl $newsletterUrl,
     TrackingConfig $trackingConfig,
-    Scheduler $scheduler
+    Scheduler $scheduler,
+    Validator $validator
   ) {
     $this->listingHandler = $listingHandler;
     $this->wp = $wp;
@@ -114,6 +119,7 @@ class Newsletters extends APIEndpoint {
     $this->newsletterUrl = $newsletterUrl;
     $this->trackingConfig = $trackingConfig;
     $this->scheduler = $scheduler;
+    $this->validator = $validator;
   }
 
   public function get($data = []) {
@@ -184,6 +190,13 @@ class Newsletters extends APIEndpoint {
       ]);
     }
 
+    if ($status === NewsletterEntity::STATUS_ACTIVE) {
+      $validationError = $this->validator->validate($newsletter);
+      if ($validationError !== null) {
+        return $this->errorResponse([APIError::FORBIDDEN => $validationError], [], Response::STATUS_FORBIDDEN);
+      }
+    }
+
     // if the re-engagement email doesn't contain the re-engage link, it can't be activated
     if ($newsletter->getType() === NewsletterEntity::TYPE_RE_ENGAGEMENT && $status === NewsletterEntity::STATUS_ACTIVE) {
       if (strpos($newsletter->getContent(), '[link:subscription_re_engage_url]') === false) {
diff --git a/mailpoet/lib/Newsletter/Validator.php b/mailpoet/lib/Newsletter/Validator.php
index daebde800b..041b04aecb 100644
--- a/mailpoet/lib/Newsletter/Validator.php
+++ b/mailpoet/lib/Newsletter/Validator.php
@@ -22,21 +22,31 @@ class Validator {
       && is_array($newsletterEntity->getBody())
       && $newsletterEntity->getBody()['content']
     ) {
-      $body = json_encode($newsletterEntity->getBody()['content']);
-      if ($body === false) {
-        return __('Poet, please add prose to your masterpiece before you send it to your followers.');
+      $content = $newsletterEntity->getBody()['content'];
+      $encodedBody = json_encode($content);
+      if ($encodedBody === false) {
+        return $this->emptyContentErrorMessage();
+      } else {
+        $blocks = $content['blocks'] ?? [];
+        if (empty($blocks)) {
+          return $this->emptyContentErrorMessage();
+        }
       }
 
       if (
         $this->bridge->isMailpoetSendingServiceEnabled()
-        && (strpos($body, '[link:subscription_unsubscribe_url]') === false)
-        && (strpos($body, '[link:subscription_unsubscribe]') === false)
+        && (strpos($encodedBody, '[link:subscription_unsubscribe_url]') === false)
+        && (strpos($encodedBody, '[link:subscription_unsubscribe]') === false)
       ) {
         return __('All emails must include an "Unsubscribe" link. Add a footer widget to your email to continue.');
       }
     } else {
-      return __('Poet, please add prose to your masterpiece before you send it to your followers.');
+      return $this->emptyContentErrorMessage();
     }
     return null;
   }
+  
+  private function emptyContentErrorMessage(): string {
+    return __('Poet, please add prose to your masterpiece before you send it to your followers.');
+  }
 }
diff --git a/mailpoet/tests/integration/API/JSON/v1/NewslettersTest.php b/mailpoet/tests/integration/API/JSON/v1/NewslettersTest.php
index f92f974594..e3c01f9fc5 100644
--- a/mailpoet/tests/integration/API/JSON/v1/NewslettersTest.php
+++ b/mailpoet/tests/integration/API/JSON/v1/NewslettersTest.php
@@ -36,6 +36,7 @@ use MailPoet\Newsletter\Segment\NewsletterSegmentRepository;
 use MailPoet\Newsletter\Sending\SendingQueuesRepository;
 use MailPoet\Newsletter\Statistics\NewsletterStatisticsRepository;
 use MailPoet\Newsletter\Url;
+use MailPoet\Newsletter\Validator;
 use MailPoet\Router\Router;
 use MailPoet\Segments\SegmentsRepository;
 use MailPoet\Settings\SettingsController;
@@ -695,14 +696,15 @@ class NewslettersTest extends \MailPoetTest {
       $this->diContainer->get(NewsletterSaveController::class),
       $this->diContainer->get(Url::class),
       $this->diContainer->get(TrackingConfig::class),
-      $this->scheduler
+      $this->scheduler,
+      $this->diContainer->get(Validator::class)
     );
   }
 
   private function createNewsletter(string $subject, string $type): NewsletterEntity {
     $newsletter = new NewsletterEntity();
     $newsletter->setSubject($subject);
-    $newsletter->setBody(Fixtures::get('newsletter_body_template'));
+    $newsletter->setBody((array)json_decode(Fixtures::get('newsletter_body_template'), true));
     $newsletter->setType($type);
     $newsletter->setHash(Security::generateHash());
     $this->newsletterRepository->persist($newsletter);
diff --git a/mailpoet/tests/integration/API/JSON/v1/SendingQueueTest.php b/mailpoet/tests/integration/API/JSON/v1/SendingQueueTest.php
index ed611f5be9..5bed592049 100644
--- a/mailpoet/tests/integration/API/JSON/v1/SendingQueueTest.php
+++ b/mailpoet/tests/integration/API/JSON/v1/SendingQueueTest.php
@@ -143,7 +143,21 @@ class SendingQueueTest extends \MailPoetTest {
     $newsletter = new NewsletterEntity();
     $newsletter->setSubject('subject');
     $newsletter->setType(NewsletterEntity::TYPE_STANDARD);
-    $newsletter->setBody(['content' => ['type' => 'container', 'columnLayout' => false, 'orientation' => 'vertical']]);
+    $newsletter->setBody([
+      'content' =>
+        [
+          'type' => 'container',
+          'columnLayout' => false,
+          'orientation' => 'vertical',
+          'blocks' => [
+            [
+              'type' => 'header',
+              'link' => '',
+              'text' => 'Hello!'
+            ]
+          ]
+        ]
+    ]);
     $this->entityManager->persist($newsletter);
     $this->entityManager->flush();
     $sendingQueue = new SendingQueueAPI(
@@ -165,6 +179,20 @@ class SendingQueueTest extends \MailPoetTest {
     expect($response['errors'][0]['error'])->stringContainsString('bad_request');
   }
 
+  public function testItRejectsNewslettersWithoutContentBlocks() {
+    $newsletter = new NewsletterEntity();
+    $newsletter->setSubject('subject');
+    $newsletter->setType(NewsletterEntity::TYPE_STANDARD);
+    $newsletter->setBody(['content' => ['type' => 'container', 'columnLayout' => false, 'orientation' => 'vertical']]);
+    $this->entityManager->persist($newsletter);
+    $this->entityManager->flush();
+    $sendingQueue = $this->diContainer->get(SendingQueueAPI::class);
+    $response = $sendingQueue->add(['newsletter_id' => $newsletter->getId()]);
+    $result = $response->getData();
+    expect($result['errors'][0])->array();
+    expect($result['errors'][0]['message'])->stringContainsString('Poet, please add prose to your masterpiece before you send it to your followers');
+  }
+
   private function _createOrUpdateNewsletterOptions(NewsletterEntity $newsletter, $newsletterType, $options) {
     $newsletterOptionFieldRepository = $this->diContainer->get(NewsletterOptionFieldsRepository::class);
     $newsletterOptionRepository = $this->diContainer->get(NewsletterOptionsRepository::class);