diff --git a/core/modules/system/config/install/system.site.yml b/core/modules/system/config/install/system.site.yml
index 4ec5420035f56abe951d4b872a441fb72300ddca..5f63ba915df0d66461845641dc8b71a2a0a5fc43 100644
--- a/core/modules/system/config/install/system.site.yml
+++ b/core/modules/system/config/install/system.site.yml
@@ -10,3 +10,4 @@ page:
 admin_compact_mode: false
 weight_select_max: 100
 default_langcode: en
+mail_notification: null
diff --git a/core/modules/system/system.post_update.php b/core/modules/system/system.post_update.php
index f027b80634f4283126d1af8cc5cf3b8ab537ef2d..6cfd3ad7d06997d01d168f784744b89725e23815 100644
--- a/core/modules/system/system.post_update.php
+++ b/core/modules/system/system.post_update.php
@@ -201,3 +201,14 @@ function system_post_update_amend_config_sync_readme_url() {
   file_put_contents($readme_path, $changed_content);
   return \t('Amended configuration synchronization readme file content.');
 }
+
+/**
+ * Adds default value for the mail_notification config parameter.
+ */
+function system_post_update_mail_notification_setting() {
+  $config = \Drupal::configFactory()->getEditable('system.site');
+  // If the value doesn't exist it always returns NULL.
+  if (is_null($config->get('mail_notification'))) {
+    $config->set('mail_notification', NULL)->save();
+  }
+}
diff --git a/core/modules/system/tests/src/Kernel/Migrate/d6/MigrateSystemConfigurationTest.php b/core/modules/system/tests/src/Kernel/Migrate/d6/MigrateSystemConfigurationTest.php
index f5f2971fbb944a2e72e7e290ebbfda326d16581b..cfc708e5a326c861038f9c4c002d55c133f5d299 100644
--- a/core/modules/system/tests/src/Kernel/Migrate/d6/MigrateSystemConfigurationTest.php
+++ b/core/modules/system/tests/src/Kernel/Migrate/d6/MigrateSystemConfigurationTest.php
@@ -109,6 +109,7 @@ class MigrateSystemConfigurationTest extends MigrateDrupal6TestBase {
       'admin_compact_mode' => FALSE,
       'weight_select_max' => 100,
       'default_langcode' => 'en',
+      'mail_notification' => NULL,
     ],
   ];
 
diff --git a/core/modules/system/tests/src/Kernel/Migrate/d7/MigrateSystemConfigurationTest.php b/core/modules/system/tests/src/Kernel/Migrate/d7/MigrateSystemConfigurationTest.php
index 4ace54e849926e7367519cb91328e714c559de91..1e6e247517306440703ed15ceefd4a39e842174c 100644
--- a/core/modules/system/tests/src/Kernel/Migrate/d7/MigrateSystemConfigurationTest.php
+++ b/core/modules/system/tests/src/Kernel/Migrate/d7/MigrateSystemConfigurationTest.php
@@ -118,6 +118,7 @@ class MigrateSystemConfigurationTest extends MigrateDrupal7TestBase {
       'admin_compact_mode' => TRUE,
       'weight_select_max' => 100,
       'default_langcode' => 'en',
+      'mail_notification' => NULL,
     ],
   ];
 
diff --git a/core/profiles/demo_umami/config/install/system.site.yml b/core/profiles/demo_umami/config/install/system.site.yml
index cc529097b646efb42327b51d18eb915ebcd47721..12bfabeb6774ea191f2b4c99aa1fce492354444f 100644
--- a/core/profiles/demo_umami/config/install/system.site.yml
+++ b/core/profiles/demo_umami/config/install/system.site.yml
@@ -10,3 +10,4 @@ page:
 admin_compact_mode: false
 weight_select_max: 100
 default_langcode: en
+mail_notification: null
diff --git a/core/profiles/standard/config/install/system.site.yml b/core/profiles/standard/config/install/system.site.yml
index cc529097b646efb42327b51d18eb915ebcd47721..12bfabeb6774ea191f2b4c99aa1fce492354444f 100644
--- a/core/profiles/standard/config/install/system.site.yml
+++ b/core/profiles/standard/config/install/system.site.yml
@@ -10,3 +10,4 @@ page:
 admin_compact_mode: false
 weight_select_max: 100
 default_langcode: en
+mail_notification: null
diff --git a/core/profiles/testing_config_overrides/config/install/system.site.yml b/core/profiles/testing_config_overrides/config/install/system.site.yml
index 6b9711224ebc7e2cb67e1e5b6bbc65c0a5092ea0..c51549bcdb6ada00a7e11ce271599ac2325da92d 100644
--- a/core/profiles/testing_config_overrides/config/install/system.site.yml
+++ b/core/profiles/testing_config_overrides/config/install/system.site.yml
@@ -10,3 +10,4 @@ page:
 admin_compact_mode: false
 weight_select_max: 91
 default_langcode: en
+mail_notification: null