diff --git a/app/Livewire/Admin/Maintenance.php b/app/Livewire/Admin/Maintenance.php
index b066c30..afe3de8 100644
--- a/app/Livewire/Admin/Maintenance.php
+++ b/app/Livewire/Admin/Maintenance.php
@@ -129,10 +129,13 @@ 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));
-                $delivery->update(['sent_at' => now()]);
             }
         }
     }
diff --git a/app/Livewire/Admin/Settings.php b/app/Livewire/Admin/Settings.php
index a75a330..df0865b 100644
--- a/app/Livewire/Admin/Settings.php
+++ b/app/Livewire/Admin/Settings.php
@@ -49,6 +49,15 @@ class Settings extends Component
             'name' => 'required|string|max:255',
             'email' => 'required|email|max:255|unique:users,email,'.$user->id,
         ]);
+
+        // An operator email must never collide with a customer's — that would
+        // block the customer from ever obtaining a portal login (ensureUser).
+        if (Customer::query()->where('email', $data['email'])->exists()) {
+            $this->addError('email', __('admin_settings.is_customer'));
+
+            return;
+        }
+
         $user->update($data);
         $this->dispatch('notify', message: __('admin_settings.account_saved'));
     }