diff --git a/app/Providers/AppServiceProvider.php b/app/Providers/AppServiceProvider.php
index 43f2575..98f0e44 100644
--- a/app/Providers/AppServiceProvider.php
+++ b/app/Providers/AppServiceProvider.php
@@ -49,28 +49,27 @@ class AppServiceProvider extends ServiceProvider
     public function boot(): void
     {
         // Send-time guard for maintenance mail (X-CP-Notification carries the
-        // ledger id). Two things happen atomically here so exactly one copy ships
-        // even if a backlog caused a duplicate job to be queued:
-        //   1) suppress an announcement whose window was cancelled meanwhile;
-        //   2) claim delivery with a conditional update — the first send wins,
-        //      any duplicate finds sent_at already set and is aborted.
+        // ledger id). Read-only — it never marks the row sent (that happens on
+        // real delivery in MessageSent, so a transport failure stays retryable).
+        // It aborts a send when the window was cancelled meanwhile, or when a
+        // sibling copy already delivered (sent_at set) — the common backlog dedup.
         Event::listen(MessageSending::class, function (MessageSending $event) {
             $header = $event->message->getHeaders()->get('X-CP-Notification');
             if ($header === null) {
                 return null;
             }
-            $id = (int) $header->getBodyAsString();
-            $notification = MaintenanceNotification::query()->with('window')->find($id);
+            $notification = MaintenanceNotification::query()->with('window')->find((int) $header->getBodyAsString());
             if ($notification === null) {
                 return null;
             }
+            if ($notification->sent_at !== null) {
+                return false; // already delivered — suppress a duplicate copy
+            }
             if ($notification->event === 'announcement' && $notification->window?->state === 'cancelled') {
                 return false; // window cancelled meanwhile — do not deliver
             }
 
-            $claimed = MaintenanceNotification::query()->whereKey($id)->whereNull('sent_at')->update(['sent_at' => now()]);
-
-            return $claimed === 0 ? false : null; // 0 → already delivered, suppress duplicate
+            return null;
         });
 
         // Stamp a maintenance-notification ledger row as delivered only once the