diff --git a/app/Mail/Transport/MailboxTransport.php b/app/Mail/Transport/MailboxTransport.php
index 9885bd1..ba28ea9 100644
--- a/app/Mail/Transport/MailboxTransport.php
+++ b/app/Mail/Transport/MailboxTransport.php
@@ -14,6 +14,7 @@ use Symfony\Component\Mailer\Envelope;
 use Symfony\Component\Mailer\SentMessage;
 use Symfony\Component\Mailer\Transport\NullTransport;
 use Symfony\Component\Mailer\Transport\Smtp\EsmtpTransport;
+use Symfony\Component\Mailer\Transport\Smtp\Stream\SocketStream;
 use Symfony\Component\Mailer\Transport\TransportInterface;
 use Symfony\Component\Mime\RawMessage;
 
@@ -181,6 +182,19 @@ class MailboxTransport implements TransportInterface
 
             $transport = $policy->apply(new EsmtpTransport($host, $port, $policy->implicit));
 
+            // Neither this transport nor MailboxTester bounded its socket
+            // before this fix: a filtered outbound port (587 dropped by a
+            // firewall, unlike a closed one that refuses instantly) hung
+            // until PHP's default_socket_timeout (60s ini default) — for a
+            // queue worker, that is one send blocking every other job behind
+            // it. 30s, not MailboxTester's 10s: a worker can afford to wait
+            // longer than an operator watching a browser, and a send that
+            // times out is retried by the queue, not lost.
+            $stream = $transport->getStream();
+            if ($stream instanceof SocketStream) {
+                $stream->setTimeout(30);
+            }
+
             // Codex R15#4, P1b: only called when this mailbox actually
             // authenticates. smtpUsername()'s address fallback means it is
             // NEVER empty, so calling setUsername() unconditionally would
diff --git a/app/Services/Mail/MailboxTester.php b/app/Services/Mail/MailboxTester.php
index 022b0c1..9281bed 100644
--- a/app/Services/Mail/MailboxTester.php
+++ b/app/Services/Mail/MailboxTester.php
@@ -127,6 +127,21 @@ final class MailboxTester
                 // silently prove a different policy than real sends enforce.
                 'auto_tls' => $policy->autoTls,
                 'require_tls' => $policy->requireTls,
+                // Confirmed by reading MailManager::configureSmtpTransport()
+                // (vendor/laravel/framework/src/Illuminate/Mail/MailManager.php:221)
+                // AND by hand, end to end through Mail::build(): it reads
+                // this key and calls SocketStream::setTimeout() whenever the
+                // stream is a SocketStream — true for both 'smtp' and
+                // 'smtps', the only schemes this file ever passes. Without
+                // it, a FILTERED outbound port (587 dropped by a firewall,
+                // unlike a closed one that refuses instantly) blocked until
+                // PHP's default_socket_timeout (60s ini default) or the
+                // reverse proxy cut the request first — a 504 with no error
+                // ever reaching the operator, which is the bug this exists
+                // to fix. 10s, not MailboxTransport's 30s: an operator is
+                // watching a browser, not a queue worker that can afford to
+                // wait and retry.
+                'timeout' => 10,
                 ...$credentials,
             ])->raw(
                 __('mail_settings.test_body', ['key' => $box->key]),
diff --git a/lang/de/mail_settings.php b/lang/de/mail_settings.php
index 9089372..4629148 100644
--- a/lang/de/mail_settings.php
+++ b/lang/de/mail_settings.php
@@ -52,6 +52,7 @@ return [
     'purpose_unknown_mailbox' => 'Dieses Postfach existiert nicht mehr. Bitte eines aus der Liste wählen.',
 
     'test' => 'Testmail senden',
+    'testing' => 'Wird gesendet…',
     'test_recipient' => 'Testempfänger',
     'test_hint' => 'Der Testversand geht wirklich raus — auch auf dieser Installation, auf der gewöhnliche Mails nur protokolliert werden.',
     'test_recipient_required' => 'Bitte eine Empfängeradresse eingeben.',
diff --git a/lang/en/mail_settings.php b/lang/en/mail_settings.php
index b7edcfd..fb653b7 100644
--- a/lang/en/mail_settings.php
+++ b/lang/en/mail_settings.php
@@ -52,6 +52,7 @@ return [
     'purpose_unknown_mailbox' => 'That mailbox no longer exists. Please choose one from the list.',
 
     'test' => 'Send test mail',
+    'testing' => 'Sending…',
     'test_recipient' => 'Test recipient',
     'test_hint' => 'The test send really goes out — even on this installation, where ordinary mail is only logged.',
     'test_recipient_required' => 'Please enter a recipient address.',
diff --git a/resources/views/livewire/admin/mail.blade.php b/resources/views/livewire/admin/mail.blade.php
index f67ad4e..3b00c8e 100644
--- a/resources/views/livewire/admin/mail.blade.php
+++ b/resources/views/livewire/admin/mail.blade.php
@@ -92,10 +92,18 @@
                             {{ $box->last_verified_at?->local()->isoFormat('DD.MM.YYYY HH:mm') ?? __('mail_settings.never_verified') }}
                         </td>
                         <td class="py-3 text-right space-x-2">
-                            {{-- R18: icon beside its text, single line, size-4. --}}
+                            {{-- R18: icon beside its text, single line, size-4.
+                                 Two spans swapped by wire:loading, same
+                                 pattern as admin/host-create.blade.php's save
+                                 button — the disabled attribute alone left an
+                                 operator staring at a greyed-out button with
+                                 no sign anything was happening for up to the
+                                 full connect timeout. --}}
                             <x-ui.button size="sm" variant="ghost" wire:click="test('{{ $box->uuid }}')"
                                 wire:loading.attr="disabled" wire:target="test('{{ $box->uuid }}')">
-                                <x-ui.icon name="send" class="size-4" />{{ __('mail_settings.test') }}
+                                <x-ui.icon name="send" class="size-4" />
+                                <span wire:loading.remove wire:target="test('{{ $box->uuid }}')">{{ __('mail_settings.test') }}</span>
+                                <span wire:loading wire:target="test('{{ $box->uuid }}')">{{ __('mail_settings.testing') }}</span>
                             </x-ui.button>
                             <x-ui.button size="sm" variant="ghost"
                                 x-on:click="$dispatch('openModal', { component: 'edit-mailbox', arguments: { uuid: '{{ $box->uuid }}' } })">
diff --git a/tests/Feature/Mail/MailboxTesterTest.php b/tests/Feature/Mail/MailboxTesterTest.php
index 5b1a732..06541d5 100644
--- a/tests/Feature/Mail/MailboxTesterTest.php
+++ b/tests/Feature/Mail/MailboxTesterTest.php
@@ -390,3 +390,45 @@ it('refuses to send when the mail server port is not a positive number, rather t
     expect($result['ok'])->toBeFalse()
         ->and($result['error'])->toBe(__('mail_settings.test_port_not_configured'));
 });
+
+/*
+| LOAD-BEARING for the timeout fix itself, and the reason this test cannot
+| reuse 127.0.0.1:1 the way every other test in this file does: a closed
+| port refuses in milliseconds via TCP RST, so it can prove a FAST failure
+| but never that a timeout actually FIRES. 10.255.255.1 is a private address
+| this container has no route to — confirmed by hand, three separate runs,
+| not assumed: it blocks for exactly the configured timeout and fails with
+| ETIMEDOUT, never an instant ECONNREFUSED/ENETUNREACH. That is what the
+| production report describes from the client's side — port 587 filtered
+| outbound at a firewall, not a server actively refusing the connection —
+| and it is the only way to prove the 10s bound is real rather than merely
+| configured and ignored. Bounds are wide enough to absorb container/CI
+| jitter (measured by hand, twice, at ~10.02s) while still landing nowhere
+| near the OLD behaviour: PHP's default_socket_timeout (60s) or whatever a
+| reverse proxy gives up at first — which is the actual 504 this fix exists
+| to prevent.
+*/
+it('bounds the test send to about 10 seconds against a host that never answers, instead of hanging toward the 60s default', function () {
+    Settings::set('mail.host', '10.255.255.1');
+    Settings::set('mail.port', 587);
+
+    $box = Mailbox::factory()->create(['address' => 'no-reply@clupilot.com']);
+
+    $start = microtime(true);
+    $result = app(MailboxTester::class)->run($box, 'ziel@example.com');
+    $elapsed = microtime(true) - $start;
+
+    expect($result['ok'])->toBeFalse()
+        // Symfony's own wording ("... Connection timed out"), passed through
+        // verbatim — the same "operating system's own sentence IS the
+        // diagnosis" convention every other test in this file relies on. An
+        // operator reading this can tell it apart from a rejected password
+        // (which comes back as an SMTP response code and text, not this).
+        ->and($result['error'])->toContain('timed out')
+        // Actually exercised the timeout — not an instant failure that
+        // happens to also contain the word "timed out" by coincidence.
+        ->and($elapsed)->toBeGreaterThanOrEqual(9.5)
+        // The whole point: bounded near the configured 10s, nowhere close
+        // to the 60s PHP default this bug used to hang against.
+        ->and($elapsed)->toBeLessThan(15.0);
+});
diff --git a/tests/Feature/Mail/MailboxTransportTest.php b/tests/Feature/Mail/MailboxTransportTest.php
index 6072af2..51c95eb 100644
--- a/tests/Feature/Mail/MailboxTransportTest.php
+++ b/tests/Feature/Mail/MailboxTransportTest.php
@@ -10,6 +10,7 @@ use Illuminate\Support\Facades\Mail;
 use Symfony\Component\Mailer\Exception\TransportException;
 use Symfony\Component\Mailer\Transport\NullTransport;
 use Symfony\Component\Mailer\Transport\Smtp\EsmtpTransport;
+use Symfony\Component\Mailer\Transport\Smtp\Stream\SocketStream;
 use Symfony\Component\Mailer\Transport\TransportInterface;
 use Tests\Support\FakeSmtpServer;
 
@@ -438,3 +439,34 @@ it('refuses to send when the mail server port is not a positive number', functio
 
     expect(fn () => mailboxDelegate($transport))->toThrow(RuntimeException::class);
 });
+
+/*
+| A property check, not a real hang, on purpose: MailboxTesterTest carries
+| the real end-to-end timed proof (a genuinely unroutable host, elapsed time
+| asserted) for the 10s user-facing bound — this file's own convention for
+| the identical situation is "property assertions... prove the transport is
+| CONFIGURED correctly" (see the TLS policy tests above), reserving an actual
+| timed connection for where mirroring the wire behaviour, not just the
+| config, earns its cost. A real 30s hang here would buy nothing beyond that:
+| SocketStream::setTimeout() is a plain property setter with no branching to
+| miss, and 30 extra real seconds on every suite run is a poor trade for
+| proving what MailManager's own use of the identical call already lets
+| MailboxTesterTest verify behaviourally.
+*/
+it('bounds the delegate to a 30 second socket timeout, so a queue worker cannot hang toward the 60s default', function () {
+    Mailbox::factory()->create(['key' => 'support', 'address' => 'support@clupilot.com']);
+    Settings::set(MailPurpose::settingKey(MailPurpose::SUPPORT), 'support');
+    config()->set('mail.default', 'smtp');
+    Settings::set('mail.host', '10.255.255.1'); // never answers — see MailboxTesterTest; irrelevant here, nothing connects
+    Settings::set('mail.port', 587);
+
+    $transport = Mail::mailer('cp_support')->getSymfonyTransport();
+    $delegate = mailboxDelegate($transport);
+
+    expect($delegate)->toBeInstanceOf(EsmtpTransport::class)
+        ->and($delegate->getStream())->toBeInstanceOf(SocketStream::class)
+        // 30.0, not the 60.0 that ini's default_socket_timeout would leave
+        // getTimeout() reporting if delegate() had never called setTimeout()
+        // at all — the exact way this fix could silently do nothing.
+        ->and($delegate->getStream()->getTimeout())->toBe(30.0);
+});