diff --git a/app/Livewire/Admin/Maintenance.php b/app/Livewire/Admin/Maintenance.php
index afe3de8..8a9f27a 100644
--- a/app/Livewire/Admin/Maintenance.php
+++ b/app/Livewire/Admin/Maintenance.php
@@ -8,6 +8,7 @@ use App\Models\Host;
 use App\Models\MaintenanceNotification;
 use App\Models\MaintenanceWindow;
 use Illuminate\Support\Carbon;
+use Illuminate\Support\Facades\DB;
 use Illuminate\Support\Facades\Mail;
 use Livewire\Attributes\Layout;
 use Livewire\Attributes\Validate;
@@ -51,7 +52,15 @@ class Maintenance extends Component
 
     private function persist(string $state): ?MaintenanceWindow
     {
-        $data = $this->validate();
+        $data = $this->validate([
+            'title' => 'required|string|max:255',
+            'publicDescription' => 'nullable|string|max:2000',
+            'internalNotes' => 'nullable|string|max:2000',
+            'startsAt' => 'required|date',
+            'endsAt' => 'required|date',
+            'hostIds' => 'array',
+            'hostIds.*' => 'integer|exists:hosts,id',
+        ]);
 
         $starts = Carbon::parse($data['startsAt']);
         $ends = Carbon::parse($data['endsAt']);
@@ -74,17 +83,23 @@ class Maintenance extends Component
             }
         }
 
-        $window = MaintenanceWindow::create([
-            'title' => $data['title'],
-            'public_description' => $data['publicDescription'] ?: null,
-            'internal_notes' => $data['internalNotes'] ?: null,
-            'starts_at' => $starts,
-            'ends_at' => $ends,
-            'state' => $state,
-            'created_by' => auth()->id(),
-            'published_at' => $state === 'scheduled' ? now() : null,
-        ]);
-        $window->hosts()->sync(array_map('intval', $this->hostIds));
+        // Create the window and attach hosts atomically so a bad id can't leave
+        // an orphaned scheduled window behind.
+        $window = DB::transaction(function () use ($data, $starts, $ends, $state) {
+            $window = MaintenanceWindow::create([
+                'title' => $data['title'],
+                'public_description' => $data['publicDescription'] ?: null,
+                'internal_notes' => $data['internalNotes'] ?: null,
+                'starts_at' => $starts,
+                'ends_at' => $ends,
+                'state' => $state,
+                'created_by' => auth()->id(),
+                'published_at' => $state === 'scheduled' ? now() : null,
+            ]);
+            $window->hosts()->sync(array_map('intval', $data['hostIds'] ?? []));
+
+            return $window;
+        });
 
         $this->reset('title', 'publicDescription', 'internalNotes', 'startsAt', 'endsAt', 'hostIds');
         $this->dispatch('notify', message: __($state === 'scheduled' ? 'maintenance.published' : 'maintenance.draft_saved'));
@@ -129,13 +144,19 @@ class Maintenance extends Component
                 ['email' => $customer->email],
             );
             if ($delivery->wasRecentlyCreated) {
-                // The ledger row (created here) is the idempotency marker so we
-                // queue at most once per customer. sent_at stays null until the
-                // mail is actually delivered — a MessageSent listener could stamp
-                // it later; we never claim delivery merely on dispatch.
-                Mail::to($customer->email)
-                    ->locale($customer->locale ?: config('app.locale'))
-                    ->queue(new MaintenanceAnnouncementMail($window, $customer));
+                // The ledger row is the idempotency marker (queue at most once).
+                // If dispatch itself fails, drop the row so a re-publish retries;
+                // sent_at stays null until real delivery (a MessageSent listener
+                // could stamp it) — we never claim delivery merely on dispatch.
+                try {
+                    Mail::to($customer->email)
+                        ->locale($customer->locale ?: config('app.locale'))
+                        ->queue(new MaintenanceAnnouncementMail($window, $customer));
+                } catch (\Throwable $e) {
+                    $delivery->delete();
+
+                    throw $e;
+                }
             }
         }
     }
diff --git a/app/Livewire/Admin/Settings.php b/app/Livewire/Admin/Settings.php
index df0865b..7f9835e 100644
--- a/app/Livewire/Admin/Settings.php
+++ b/app/Livewire/Admin/Settings.php
@@ -112,6 +112,11 @@ class Settings extends Component
             if ($target->id === auth()->id()) {
                 return 'self';
             }
+            // Only existing operators may be re-roled — never escalate a customer
+            // (or any non-staff) user into the console via a tampered id.
+            if (! $target->isOperator() || Customer::query()->where('email', $target->email)->exists()) {
+                return 'not_staff';
+            }
             // Granting or revoking Owner is Owner-only.
             if (($role === 'Owner' || $target->hasRole('Owner')) && ! auth()->user()->hasRole('Owner')) {
                 return 'owner_only';
@@ -134,7 +139,7 @@ class Settings extends Component
 
         $result = DB::transaction(function () use ($id) {
             $target = User::query()->whereKey($id)->lockForUpdate()->first();
-            if ($target === null) {
+            if ($target === null || ! $target->isOperator()) {
                 return 'gone';
             }
             if ($target->id === auth()->id()) {
@@ -160,6 +165,7 @@ class Settings extends Component
             'self' => __('admin_settings.not_self'),
             'owner_only' => __('admin_settings.owner_only'),
             'last_owner' => __('admin_settings.last_owner'),
+            'not_staff' => __('admin_settings.not_staff'),
             default => null,
         };
         if ($msg !== null) {
diff --git a/lang/de/admin_settings.php b/lang/de/admin_settings.php
index 4592d43..d93a0e0 100644
--- a/lang/de/admin_settings.php
+++ b/lang/de/admin_settings.php
@@ -34,5 +34,6 @@ return [
     'not_self' => 'Sie können Ihre eigene Rolle nicht ändern.',
     'owner_only' => 'Nur ein Inhaber darf die Inhaber-Rolle vergeben oder entziehen.',
     'last_owner' => 'Der letzte Inhaber kann nicht geändert oder entfernt werden.',
+    'not_staff' => 'Nur bestehende Mitarbeiter können bearbeitet werden.',
     'is_customer' => 'Diese E-Mail gehört bereits zu einem Kundenkonto.',
 ];
diff --git a/lang/en/admin_settings.php b/lang/en/admin_settings.php
index 783ecde..c788f68 100644
--- a/lang/en/admin_settings.php
+++ b/lang/en/admin_settings.php
@@ -34,5 +34,6 @@ return [
     'not_self' => 'You cannot change your own role.',
     'owner_only' => 'Only an Owner may grant or revoke the Owner role.',
     'last_owner' => 'The last Owner cannot be changed or removed.',
+    'not_staff' => 'Only existing staff can be edited.',
     'is_customer' => 'This email already belongs to a customer account.',
 ];
diff --git a/tests/Feature/Admin/AdminSettingsTest.php b/tests/Feature/Admin/AdminSettingsTest.php
index e3edbd5..dec24e7 100644
--- a/tests/Feature/Admin/AdminSettingsTest.php
+++ b/tests/Feature/Admin/AdminSettingsTest.php
@@ -40,6 +40,14 @@ it('will not create an operator from a customer email', function () {
         ->call('inviteStaff')->assertHasErrors(['staffEmail']);
 });
 
+it('will not escalate a non-staff user via a tampered id', function () {
+    $victim = User::factory()->create(); // a plain (customer) user, no role
+
+    Livewire::actingAs(operator('Owner'))->test(Settings::class)->call('setStaffRole', $victim->id, 'Admin');
+
+    expect($victim->fresh()->isOperator())->toBeFalse();
+});
+
 it('protects the last owner and self-role', function () {
     $owner = operator('Owner');
     $support = operator('Support');