diff --git a/app/Mail/Transport/MailboxTransport.php b/app/Mail/Transport/MailboxTransport.php
new file mode 100644
index 0000000..0137540
--- /dev/null
+++ b/app/Mail/Transport/MailboxTransport.php
@@ -0,0 +1,106 @@
+<?php
+
+namespace App\Mail\Transport;
+
+use App\Services\Mail\MailboxResolver;
+use App\Support\Settings;
+use Illuminate\Mail\Transport\LogTransport;
+use Illuminate\Support\Facades\Log;
+use Symfony\Component\Mailer\Envelope;
+use Symfony\Component\Mailer\SentMessage;
+use Symfony\Component\Mailer\Transport\Smtp\EsmtpTransport;
+use Symfony\Component\Mailer\Transport\TransportInterface;
+use Symfony\Component\Mime\RawMessage;
+
+/**
+ * Resolves its credentials when it sends, not when it is built.
+ *
+ * The mails are queued. A worker builds its mailer once and lives for hours, so
+ * anything decided in a constructor is decided for the rest of that worker's
+ * life — including a password the operator has since corrected in the console.
+ *
+ * The delegate is cached against a FINGERPRINT of the credentials rather than
+ * rebuilt per message: correct when they change, and no new SMTP connection per
+ * mail when they do not.
+ */
+class MailboxTransport implements TransportInterface
+{
+    private ?TransportInterface $delegate = null;
+
+    private ?string $fingerprint = null;
+
+    public function __construct(private readonly string $purpose) {}
+
+    public function send(RawMessage $message, ?Envelope $envelope = null): ?SentMessage
+    {
+        return $this->delegate()->send($message, $envelope);
+    }
+
+    public function __toString(): string
+    {
+        return 'mailbox://'.$this->purpose.'/'.($this->describe() ?? 'unconfigured');
+    }
+
+    /** What this transport currently points at — used by __toString and tests. */
+    private function describe(): ?string
+    {
+        if ($this->isLogging()) {
+            return 'log';
+        }
+
+        return app(MailboxResolver::class)->for($this->purpose)?->address;
+    }
+
+    /**
+     * Delivery is off wherever the default mailer is the log.
+     *
+     * This is what keeps a development machine from mailing real customers: the
+     * mailables name a purpose, so without this check they would bypass
+     * MAIL_MAILER=log entirely and send for real.
+     */
+    private function isLogging(): bool
+    {
+        return config('mail.default') === 'log';
+    }
+
+    private function delegate(): TransportInterface
+    {
+        if ($this->isLogging()) {
+            return new LogTransport(Log::channel(config('mail.mailers.log.channel')));
+        }
+
+        $box = app(MailboxResolver::class)->for($this->purpose);
+
+        if ($box === null || ! $box->isConfigured()) {
+            // Loud, not silent: a mail with no mailbox behind it must not look
+            // like it was sent.
+            throw new \RuntimeException(
+                "No configured mailbox for mail purpose [{$this->purpose}]."
+            );
+        }
+
+        $host = (string) Settings::get('mail.host', '');
+        $port = (int) Settings::get('mail.port', 587);
+        $encryption = (string) Settings::get('mail.encryption', 'tls');
+
+        $fingerprint = md5(implode('|', [
+            $host, $port, $encryption, $box->smtpUsername(), (string) $box->password,
+        ]));
+
+        if ($this->delegate === null || $this->fingerprint !== $fingerprint) {
+            // The third argument is IMPLICIT TLS (smtps, port 465) — not
+            // STARTTLS. EsmtpTransport negotiates STARTTLS by itself on a
+            // plain connection, which is what port 587 wants. Passing true for
+            // 'tls' here would open an SSL socket against a server expecting
+            // STARTTLS and hang.
+            $transport = new EsmtpTransport($host, $port, $encryption === 'ssl' || $port === 465);
+            $transport->setUsername($box->smtpUsername());
+            $transport->setPassword((string) $box->password);
+
+            $this->delegate = $transport;
+            $this->fingerprint = $fingerprint;
+        }
+
+        return $this->delegate;
+    }
+}
diff --git a/app/Providers/AppServiceProvider.php b/app/Providers/AppServiceProvider.php
index aeab946..6929113 100644
--- a/app/Providers/AppServiceProvider.php
+++ b/app/Providers/AppServiceProvider.php
@@ -25,10 +25,12 @@ use App\Mail\MaintenanceCancelledMail;
 use App\Models\MaintenanceNotification;
 use App\Services\Maintenance\MaintenanceNotifier;
 use Carbon\CarbonImmutable;
+use App\Mail\Transport\MailboxTransport;
 use Illuminate\Mail\Events\MessageSending;
 use Illuminate\Mail\Events\MessageSent;
 use Illuminate\Support\Carbon;
 use Illuminate\Support\Facades\Event;
+use Illuminate\Support\Facades\Mail;
 use Illuminate\Support\ServiceProvider;
 use Livewire\Livewire;
 
@@ -58,6 +60,11 @@ class AppServiceProvider extends ServiceProvider
      */
     public function boot(): void
     {
+        // Registered as a DRIVER, not as configuration: the closure runs when a
+        // mailer is first resolved — inside the queue worker, at send time —
+        // so nothing here reads the database while the application boots.
+        Mail::extend('mailbox', fn (array $config) => new MailboxTransport($config['purpose']));
+
         // Every timestamp that gets shown to somebody goes through ->local()
         // first. Storage is UTC and stays UTC; this is the last step before a
         // human reads it.
diff --git a/config/mail.php b/config/mail.php
index e32e88d..a980d38 100644
--- a/config/mail.php
+++ b/config/mail.php
@@ -97,6 +97,20 @@ return [
             'retry_after' => 60,
         ],
 
+        /*
+        | One mailer per purpose. Deliberately STATIC: they name a purpose and
+        | nothing else, so building this config reads no database. Which
+        | mailbox a purpose resolves to is decided by MailboxTransport at send
+        | time — see App\Services\Secrets\SecretVault rule 3, which this
+        | follows: an overlay at boot costs a query on every request and leaves
+        | long-running queue workers holding whatever was true when they started.
+        */
+        'cp_maintenance' => ['transport' => 'mailbox', 'purpose' => 'maintenance'],
+        'cp_provisioning' => ['transport' => 'mailbox', 'purpose' => 'provisioning'],
+        'cp_support' => ['transport' => 'mailbox', 'purpose' => 'support'],
+        'cp_billing' => ['transport' => 'mailbox', 'purpose' => 'billing'],
+        'cp_system' => ['transport' => 'mailbox', 'purpose' => 'system'],
+
     ],
 
     /*
diff --git a/tests/Feature/Mail/MailboxTransportTest.php b/tests/Feature/Mail/MailboxTransportTest.php
new file mode 100644
index 0000000..6b52087
--- /dev/null
+++ b/tests/Feature/Mail/MailboxTransportTest.php
@@ -0,0 +1,78 @@
+<?php
+
+use App\Mail\Transport\MailboxTransport;
+use App\Models\Mailbox;
+use App\Services\Mail\MailPurpose;
+use App\Support\Settings;
+use Illuminate\Mail\Transport\LogTransport;
+use Illuminate\Support\Facades\Mail;
+use Symfony\Component\Mailer\Transport\Smtp\EsmtpTransport;
+
+beforeEach(function () {
+    config()->set('admin_access.secrets_key', 'base64:'.base64_encode(random_bytes(32)));
+    Settings::set('mail.host', 'mail.example.test');
+    Settings::set('mail.port', 587);
+    Settings::set('mail.encryption', 'tls');
+});
+
+it('registers a mailer per purpose without touching the database at boot', function () {
+    // The five entries exist as plain config — no query has run to build them.
+    foreach (MailPurpose::ALL as $purpose) {
+        expect(config('mail.mailers.cp_'.$purpose))
+            ->toMatchArray(['transport' => 'mailbox', 'purpose' => $purpose]);
+    }
+});
+
+it('builds the transport from the mailbox that is current at send time', function () {
+    Mailbox::factory()->create(['key' => 'support', 'address' => 'support@clupilot.com']);
+    Settings::set(MailPurpose::settingKey(MailPurpose::SUPPORT), 'support');
+    config()->set('mail.default', 'smtp'); // delivery on, as on live
+
+    $transport = Mail::mailer('cp_support')->getSymfonyTransport();
+
+    expect($transport)->toBeInstanceOf(MailboxTransport::class)
+        ->and((string) $transport)->toContain('support@clupilot.com');
+});
+
+it('logs instead of delivering while MAIL_MAILER is log', function () {
+    Mailbox::factory()->create(['key' => 'support', 'address' => 'support@clupilot.com']);
+    Settings::set(MailPurpose::settingKey(MailPurpose::SUPPORT), 'support');
+    config()->set('mail.default', 'log');
+
+    $transport = Mail::mailer('cp_support')->getSymfonyTransport();
+
+    // Still our transport — but it hands the message to the log, so a seeder
+    // run cannot mail a real customer from a development machine.
+    expect((string) $transport)->toContain('log');
+});
+
+/*
+| __toString() and send() decide "log or SMTP" through two SEPARATE code
+| paths (describe() vs delegate()). The test above only exercises the first —
+| it would keep passing even if delegate() lost its own guard and sent every
+| purpose-mailer through real SMTP regardless of MAIL_MAILER. Reach into the
+| method that actually sends, so that regression cannot hide behind a passing
+| __toString() assertion. No real socket is opened either way: EsmtpTransport
+| connects lazily on send(), never in its constructor.
+*/
+it('actually delegates to the log transport, not SMTP, while MAIL_MAILER is log', function () {
+    Mailbox::factory()->create(['key' => 'support', 'address' => 'support@clupilot.com']);
+    Settings::set(MailPurpose::settingKey(MailPurpose::SUPPORT), 'support');
+    config()->set('mail.default', 'log');
+
+    $transport = Mail::mailer('cp_support')->getSymfonyTransport();
+    $delegate = Closure::bind(fn () => $this->delegate(), $transport, MailboxTransport::class)();
+
+    expect($delegate)->toBeInstanceOf(LogTransport::class);
+});
+
+it('delegates to a real SMTP transport once MAIL_MAILER is no longer log', function () {
+    Mailbox::factory()->create(['key' => 'support', 'address' => 'support@clupilot.com']);
+    Settings::set(MailPurpose::settingKey(MailPurpose::SUPPORT), 'support');
+    config()->set('mail.default', 'smtp');
+
+    $transport = Mail::mailer('cp_support')->getSymfonyTransport();
+    $delegate = Closure::bind(fn () => $this->delegate(), $transport, MailboxTransport::class)();
+
+    expect($delegate)->toBeInstanceOf(EsmtpTransport::class);
+});