diff --git a/core/includes/file.inc b/core/includes/file.inc
index 3e5eb8c..4a8b000 100644
--- a/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -246,6 +246,16 @@ function file_create_url($uri) {
   }
 }
 
+function file_url_transform_relative_enabled($new_value = NULL) {
+  static $enabled = TRUE;
+
+  $old_value = $enabled;
+  if ($new_value !== NULL) {
+    $enabled = $new_value;
+  }
+  return $old_value;
+}
+
 /**
  * Transforms an absolute URL of a local file to a relative URL.
  *
@@ -263,6 +273,9 @@ function file_create_url($uri) {
  * @see file_create_url()
  */
 function file_url_transform_relative($file_url) {
+  if (!file_url_transform_relative_enabled()) {
+    return $file_url;
+  }
   // Unfortunately, we pretty much have to duplicate Symfony's
   // Request::getHttpHost() method because Request::getPort() may return NULL
   // instead of a port number.
diff --git a/core/lib/Drupal/Core/Mail/MailManager.php b/core/lib/Drupal/Core/Mail/MailManager.php
index 663cfd4..781fb1c 100644
--- a/core/lib/Drupal/Core/Mail/MailManager.php
+++ b/core/lib/Drupal/Core/Mail/MailManager.php
@@ -157,6 +157,9 @@ public function getInstance(array $options) {
    * {@inheritdoc}
    */
   public function mail($module, $key, $to, $langcode, $params = array(), $reply = NULL, $send = TRUE) {
+
+    $old_value = file_url_transform_relative_enabled(FALSE);
+
     $site_config = $this->configFactory->get('system.site');
     $site_mail = $site_config->get('mail');
     if (empty($site_mail)) {
@@ -243,6 +246,8 @@ public function mail($module, $key, $to, $langcode, $params = array(), $reply =
       }
     }
 
+    file_url_transform_relative_enabled($old_value);
+
     return $message;
   }