diff --git a/lib/Controllers/DefaultController.php b/lib/Controllers/DefaultController.php
index 4d2ed61..51df929 100644
--- a/lib/Controllers/DefaultController.php
+++ b/lib/Controllers/DefaultController.php
@@ -23,8 +23,8 @@ use KTXF\Resource\Identifier\EntityIdentifier;
 use KTXF\Resource\Identifier\ResourceIdentifier;
 use KTXF\Resource\Identifier\ResourceIdentifiers;
 use KTXF\Resource\Identifier\ServiceIdentifier;
-use KTXF\Mail\Provider\ProviderBaseInterface;
 use KTXF\Resource\Provider\ResourceServiceLocationInterface;
+use KTXF\Resource\SystemIdentity;
 use KTXF\Routing\Attributes\AuthenticatedRoute;
 use KTXM\MailManager\Manager;
 use Psr\Log\LoggerInterface;
@@ -86,7 +86,7 @@ class DefaultController extends ControllerAbstract {
         // acting-user override: only the reserved system context is permitted,
         // gated on the system mail management permission
         if ($user !== null && $user !== $userId) {
-            if ($user !== ProviderBaseInterface::USER_SYSTEM || !$this->identityContext->hasPermission('mail_manager.system')) {
+            if ($user !== SystemIdentity::USER || !$this->identityContext->hasPermission('mail_manager.system')) {
                 return new JsonResponse([
                     'version' => $version,
                     'transaction' => $transaction,