diff --git a/app/Http/Controllers/Api/V1/NewsletterSubscriptionController.php b/app/Http/Controllers/Api/V1/NewsletterSubscriptionController.php
index c077744d..92e58ed0 100644
--- a/app/Http/Controllers/Api/V1/NewsletterSubscriptionController.php
+++ b/app/Http/Controllers/Api/V1/NewsletterSubscriptionController.php
@@ -6,6 +6,7 @@ use App\Http\Controllers\Controller;
 use App\Http\Requests\Api\V1\SubscribeNewsletterRequest;
 use App\Models\NewsletterSubscription;
 use Illuminate\Http\JsonResponse;
+use Illuminate\Support\Facades\DB;
 use Illuminate\Support\Str;
 
 class NewsletterSubscriptionController extends Controller
@@ -14,23 +15,57 @@ class NewsletterSubscriptionController extends Controller
     {
         $validated = $request->validated();
 
-        $subscription = NewsletterSubscription::withoutGlobalScopes()->updateOrCreate(
-            [
-                'portal' => $validated['portal'],
-                'email' => mb_strtolower($validated['email']),
-            ],
-            [
+        $email = mb_strtolower($validated['email']);
+
+        $subscription = DB::transaction(function () use ($request, $validated, $email): NewsletterSubscription {
+            $subscription = NewsletterSubscription::withoutGlobalScopes()
+                ->where('portal', $validated['portal'])
+                ->where('email', $email)
+                ->lockForUpdate()
+                ->first();
+
+            // Nur ein fremder, tatsächlich gesetzter Eigentümer blockiert (409).
+            // Verwaiste Datensätze (user_id NULL nach Konto-Löschung/Legacy-Import)
+            // dürfen neu gebunden werden — sonst wäre die portal+email-Kombination
+            // dauerhaft nicht mehr abonnierbar.
+            if ($subscription !== null && $subscription->user_id !== null && $subscription->user_id !== $request->user()->id) {
+                abort(409, 'This email address is already subscribed.');
+            }
+
+            if ($subscription === null) {
+                return NewsletterSubscription::withoutGlobalScopes()->create([
+                    'portal' => $validated['portal'],
+                    'email' => $email,
+                    'user_id' => $request->user()->id,
+                    'salutation_key' => $validated['salutation_key'] ?? null,
+                    'first_name' => $validated['first_name'] ?? null,
+                    'last_name' => $validated['last_name'] ?? null,
+                    'ip_address' => $request->ip(),
+                    'is_confirmed' => false,
+                    'confirmation_token' => Str::random(32),
+                    'subscribed_at' => now(),
+                    'unsubscribed_at' => null,
+                ]);
+            }
+
+            $attributes = [
                 'user_id' => $request->user()->id,
                 'salutation_key' => $validated['salutation_key'] ?? null,
                 'first_name' => $validated['first_name'] ?? null,
                 'last_name' => $validated['last_name'] ?? null,
                 'ip_address' => $request->ip(),
-                'is_confirmed' => false,
-                'confirmation_token' => Str::random(32),
                 'subscribed_at' => now(),
                 'unsubscribed_at' => null,
-            ],
-        );
+            ];
+
+            if (! $subscription->is_confirmed) {
+                $attributes['confirmation_token'] = Str::random(32);
+            }
+
+            $subscription->update($attributes);
+
+            return $subscription;
+        });
 
         return response()->json([
             'message' => 'Newsletter subscription created.',
diff --git a/tests/Feature/Api/V1/CustomerDataApiTest.php b/tests/Feature/Api/V1/CustomerDataApiTest.php
index b5817d2f..eb62d9ce 100644
--- a/tests/Feature/Api/V1/CustomerDataApiTest.php
+++ b/tests/Feature/Api/V1/CustomerDataApiTest.php
@@ -7,10 +7,10 @@ use App\Models\User;
 use Laravel\Sanctum\Sanctum;
 use Tests\TestCase;
 
-test('unknown legacy api key requests receive gone response', function () {
+test('legacy api keys in query parameters are not accepted but get the migration hint', function () {
     /** @var TestCase $this */
-    // Übernahme 06.07.: importierte Legacy-Keys sind gültige Tokens
-    // (LegacyApiCompatibilityTest); nur unbekannte Keys bekommen 410.
+    // Legacy-Keys sind nur noch in Headern zulässig; der Query-Parameter wird
+    // nicht für die Auth genutzt, liefert aber den 410-Migrationshinweis.
     $this->getJson('/api/v1/categories?api_key=legacy-key')
         ->assertStatus(410)
         ->assertJsonStructure(['message', 'migration_url', 'docs_url']);
@@ -72,3 +72,82 @@ test('api user can subscribe an email to newsletter', function () {
         ->where('portal', 'presseecho')
         ->exists())->toBeTrue();
 });
+
+test('resubscribing keeps an existing confirmation intact', function () {
+    /** @var TestCase $this */
+    $user = User::factory()->create();
+    $subscription = NewsletterSubscription::withoutGlobalScopes()->create([
+        'portal' => 'presseecho',
+        'user_id' => $user->id,
+        'email' => 'confirmed@example.com',
+        'is_confirmed' => true,
+        'confirmation_token' => null,
+        'subscribed_at' => now()->subMonth(),
+        'unsubscribed_at' => now()->subDay(),
+    ]);
+    Sanctum::actingAs($user, ['newsletter:subscribe']);
+
+    $this->postJson('/api/v1/newsletter/subscribe', [
+        'portal' => 'presseecho',
+        'email' => 'confirmed@example.com',
+        'first_name' => 'Neu',
+    ])->assertCreated()
+        ->assertJsonPath('data.is_confirmed', true);
+
+    $subscription->refresh();
+
+    expect($subscription->is_confirmed)->toBeTrue()
+        ->and($subscription->confirmation_token)->toBeNull()
+        ->and($subscription->unsubscribed_at)->toBeNull()
+        ->and($subscription->first_name)->toBe('Neu');
+});
+
+test('an orphaned subscription without owner can be rebound instead of being permanently blocked', function () {
+    /** @var TestCase $this */
+    // user_id NULL entsteht z. B. nach Konto-Löschung (FK nullOnDelete) oder
+    // durch Legacy-Import. Ohne Rebind wäre portal+email dauerhaft gesperrt.
+    $subscription = NewsletterSubscription::withoutGlobalScopes()->create([
+        'portal' => 'presseecho',
+        'user_id' => null,
+        'email' => 'orphan@example.com',
+        'is_confirmed' => false,
+        'subscribed_at' => now()->subMonth(),
+    ]);
+
+    $user = User::factory()->create();
+    Sanctum::actingAs($user, ['newsletter:subscribe']);
+
+    $this->postJson('/api/v1/newsletter/subscribe', [
+        'portal' => 'presseecho',
+        'email' => 'orphan@example.com',
+        'first_name' => 'Wieder da',
+    ])->assertCreated();
+
+    expect($subscription->fresh()->user_id)->toBe($user->id)
+        ->and($subscription->fresh()->first_name)->toBe('Wieder da');
+});
+
+test('an api user cannot take over another newsletter subscription', function () {
+    /** @var TestCase $this */
+    $owner = User::factory()->create();
+    $attacker = User::factory()->create();
+    $subscription = NewsletterSubscription::withoutGlobalScopes()->create([
+        'portal' => 'presseecho',
+        'user_id' => $owner->id,
+        'email' => 'owned@example.com',
+        'first_name' => 'Original',
+        'is_confirmed' => true,
+        'subscribed_at' => now(),
+    ]);
+    Sanctum::actingAs($attacker, ['newsletter:subscribe']);
+
+    $this->postJson('/api/v1/newsletter/subscribe', [
+        'portal' => 'presseecho',
+        'email' => 'owned@example.com',
+        'first_name' => 'Übernommen',
+    ])->assertConflict();
+
+    expect($subscription->fresh()->user_id)->toBe($owner->id)
+        ->and($subscription->fresh()->first_name)->toBe('Original')
+        ->and($subscription->fresh()->is_confirmed)->toBeTrue();
+});