diff --git a/src/Controller/Mail/MailTestConnectionController.php b/src/Controller/Mail/MailTestConnectionController.php
index eedee6a..6d25518 100644
--- a/src/Controller/Mail/MailTestConnectionController.php
+++ b/src/Controller/Mail/MailTestConnectionController.php
@@ -23,21 +23,23 @@ class MailTestConnectionController extends AbstractController
     public function __invoke(): JsonResponse
     {
         try {
-            $folders = $this->mailProvider->listFolders();
+            $foldersCount = $this->mailProvider->testConnection();
 
             return $this->json([
                 'ok'           => true,
-                'foldersCount' => count($folders),
+                'foldersCount' => $foldersCount,
             ]);
-        } catch (MailProviderException) {
+        } catch (MailProviderException $e) {
             return $this->json([
-                'ok'    => false,
-                'error' => 'Connexion IMAP impossible. Vérifiez la configuration.',
+                'ok'     => false,
+                'error'  => 'Connexion IMAP impossible. Vérifiez la configuration.',
+                'detail' => $e->getMessage(),
             ]);
-        } catch (Throwable) {
+        } catch (Throwable $e) {
             return $this->json([
-                'ok'    => false,
-                'error' => 'Erreur inattendue lors du test de connexion.',
+                'ok'     => false,
+                'error'  => 'Erreur inattendue lors du test de connexion.',
+                'detail' => $e->getMessage(),
             ]);
         }
     }
diff --git a/src/Mail/ImapMailProvider.php b/src/Mail/ImapMailProvider.php
index 1354d1f..eac2021 100644
--- a/src/Mail/ImapMailProvider.php
+++ b/src/Mail/ImapMailProvider.php
@@ -26,6 +26,22 @@ final class ImapMailProvider implements MailProviderInterface
         private readonly LoggerInterface $logger,
     ) {}
 
+    public function testConnection(): int
+    {
+        $client = $this->getClient(requireEnabled: false);
+
+        try {
+            $folders = $client->getFolders(false);
+            $client->disconnect();
+
+            return count($folders);
+        } catch (Throwable $e) {
+            $this->logger->error('ImapMailProvider::testConnection failed: '.$e->getMessage());
+
+            throw MailProviderException::connectionFailed($e->getMessage());
+        }
+    }
+
     public function listFolders(): array
     {
         $client = $this->getClient();
@@ -269,12 +285,16 @@ final class ImapMailProvider implements MailProviderInterface
         }
     }
 
-    private function getClient(): Client
+    private function getClient(bool $requireEnabled = true): Client
     {
         $config = $this->configRepository->findSingleton();
 
-        if (null === $config || !$config->isEnabled()) {
-            throw MailProviderException::connectionFailed('Mail configuration is missing or disabled');
+        if (null === $config) {
+            throw MailProviderException::connectionFailed('Mail configuration is missing');
+        }
+
+        if ($requireEnabled && !$config->isEnabled()) {
+            throw MailProviderException::connectionFailed('Mail configuration is disabled');
         }
 
         if (null === $config->getEncryptedPassword()) {
diff --git a/src/Mail/MailProviderInterface.php b/src/Mail/MailProviderInterface.php
index 1de7da3..9392f85 100644
--- a/src/Mail/MailProviderInterface.php
+++ b/src/Mail/MailProviderInterface.php
@@ -11,6 +11,15 @@ use App\Mail\Exception\MailProviderException;
 
 interface MailProviderInterface
 {
+    /**
+     * Opens a connection using the stored configuration and returns the number
+     * of folders found. Used by the admin "test connection" endpoint, so it
+     * MUST work even when the configuration is not yet enabled.
+     *
+     * @throws MailProviderException
+     */
+    public function testConnection(): int;
+
     /**
      * Returns the full folder tree of the configured mailbox.
      *