diff --git a/mailpoet/lib/EmailEditor/Engine/EmailEditor.php b/mailpoet/lib/EmailEditor/Engine/EmailEditor.php
index e601658626..e512112b2d 100644
--- a/mailpoet/lib/EmailEditor/Engine/EmailEditor.php
+++ b/mailpoet/lib/EmailEditor/Engine/EmailEditor.php
@@ -3,12 +3,15 @@
 namespace MailPoet\EmailEditor\Engine;
 
 use MailPoet\Entities\NewsletterEntity;
+use MailPoet\Validator\Builder;
 
 /**
  * @phpstan-type EmailPostType array{name: string, args: array, meta: array{key: string, args: array}[]}
  * See register_post_type for details about EmailPostType args.
  */
 class EmailEditor {
+  public const MAILPOET_EMAIL_META_THEME_TYPE = 'mailpoet_email_theme';
+
   /** @var EmailApiController */
   private $emailApiController;
 
@@ -21,6 +24,7 @@ class EmailEditor {
   public function initialize(): void {
     do_action('mailpoet_email_editor_initialized');
     $this->registerEmailPostTypes();
+    $this->registerEmailMetaFields();
     $this->registerEmailPostSendStatus();
     $this->extendEmailPostApi();
   }
@@ -35,13 +39,23 @@ class EmailEditor {
         $postType['name'],
         array_merge($this->getDefaultEmailPostArgs(), $postType['args'])
       );
-      foreach ($postType['meta'] as $postMeta) {
-        register_post_meta(
-          $postType['name'],
-          $postMeta['key'],
-          $postMeta['args']
-        );
-      }
+    }
+  }
+
+  private function registerEmailMetaFields(): void {
+    foreach ($this->getPostTypes() as $postType) {
+      register_post_meta(
+        $postType['name'],
+        self::MAILPOET_EMAIL_META_THEME_TYPE,
+        [
+          'show_in_rest' => [
+            'schema' => $this->getEmailThemeDataSchema(),
+          ],
+          'single' => true,
+          'type' => 'object',
+          'default' => ['version' => 2], // The version 2 is important to merge themes correctly
+        ]
+      );
     }
   }
 
@@ -60,7 +74,7 @@ class EmailEditor {
       'show_ui' => true,
       'show_in_menu' => false,
       'show_in_nav_menus' => false,
-      'supports' => ['editor', 'title'],
+      'supports' => ['editor', 'title', 'custom-fields'], // 'custom-fields' is required for loading meta fields via API
       'has_archive' => true,
       'show_in_rest' => true, // Important to enable Gutenberg editor
     ];
@@ -84,4 +98,21 @@ class EmailEditor {
       'schema' => $this->emailApiController->getEmailDataSchema(),
     ]);
   }
+
+  public function getEmailThemeDataSchema(): array {
+    return Builder::object([
+      'version' => Builder::integer(),
+      'styles' => Builder::object([
+        'spacing' => Builder::object([
+          'padding' => Builder::object([
+            'top' => Builder::string(),
+            'right' => Builder::string(),
+            'bottom' => Builder::string(),
+            'left' => Builder::string(),
+          ])->nullable(),
+          'blockGap' => Builder::string()->nullable(),
+        ])->nullable(),
+      ])->nullable(),
+    ])->toArray();
+  }
 }
diff --git a/mailpoet/lib/EmailEditor/Integrations/MailPoet/EmailApiController.php b/mailpoet/lib/EmailEditor/Integrations/MailPoet/EmailApiController.php
index a4be82475a..0d6dd341af 100644
--- a/mailpoet/lib/EmailEditor/Integrations/MailPoet/EmailApiController.php
+++ b/mailpoet/lib/EmailEditor/Integrations/MailPoet/EmailApiController.php
@@ -34,7 +34,7 @@ class EmailApiController {
       'subject' => $newsletter ? $newsletter->getSubject() : '',
       'preheader' => $newsletter ? $newsletter->getPreheader() : '',
       'preview_url' => $this->newsletterUrl->getViewInBrowserUrl($newsletter),
-      'theme' => get_post_meta($postEmailData['id'], EmailEditor::MAILPOET_EMAIL_META_THEME_TYPE, true),
+      'theme' => get_post_meta($postEmailData['id'], \MailPoet\EmailEditor\Engine\EmailEditor::MAILPOET_EMAIL_META_THEME_TYPE, true),
     ];
   }
 
@@ -50,7 +50,7 @@ class EmailApiController {
       throw new UnexpectedValueException('Newsletter ID does not match the post ID');
     }
 
-    update_post_meta($emailPost->ID, EmailEditor::MAILPOET_EMAIL_META_THEME_TYPE, $data['theme']);
+    update_post_meta($emailPost->ID, \MailPoet\EmailEditor\Engine\EmailEditor::MAILPOET_EMAIL_META_THEME_TYPE, $data['theme']);
 
     $newsletter->setSubject($data['subject']);
     $newsletter->setPreheader($data['preheader']);
diff --git a/mailpoet/lib/EmailEditor/Integrations/MailPoet/EmailEditor.php b/mailpoet/lib/EmailEditor/Integrations/MailPoet/EmailEditor.php
index 0e93dcdbd4..212e366f94 100644
--- a/mailpoet/lib/EmailEditor/Integrations/MailPoet/EmailEditor.php
+++ b/mailpoet/lib/EmailEditor/Integrations/MailPoet/EmailEditor.php
@@ -10,7 +10,6 @@ use WP_Theme_JSON;
 
 class EmailEditor {
   const MAILPOET_EMAIL_POST_TYPE = 'mailpoet_email';
-  const MAILPOET_EMAIL_META_THEME_TYPE = 'mailpoet_email_theme';
 
   /** @var WPFunctions */
   private $wp;
@@ -55,17 +54,6 @@ class EmailEditor {
         ],
         'rewrite' => ['slug' => self::MAILPOET_EMAIL_POST_TYPE],
       ],
-      'meta' => [
-        [
-          'key' => self::MAILPOET_EMAIL_META_THEME_TYPE,
-          'args' => [
-            'show_in_rest' => true,
-            'single' => true,
-            'type' => 'object',
-            'default' => ['version' => 2],
-          ],
-        ],
-      ],
     ];
     return $postTypes;
   }
@@ -102,7 +90,7 @@ class EmailEditor {
   }
 
   public function extendEmailThemeStyles(WP_Theme_JSON $theme, WP_Post $post): WP_Theme_JSON {
-    $emailTheme = get_post_meta($post->ID, self::MAILPOET_EMAIL_META_THEME_TYPE, true);
+    $emailTheme = get_post_meta($post->ID, \MailPoet\EmailEditor\Engine\EmailEditor::MAILPOET_EMAIL_META_THEME_TYPE, true);
     if ($emailTheme && is_array($emailTheme)) {
       $theme->merge(new WP_Theme_JSON($emailTheme));
     }