diff --git a/app/Http/Controllers/SetupController.php b/app/Http/Controllers/SetupController.php
index 6a789c83..6c978e79 100644
--- a/app/Http/Controllers/SetupController.php
+++ b/app/Http/Controllers/SetupController.php
@@ -198,6 +198,10 @@ class SetupController extends Controller
             return !in_array($input->env['mail_driver'], ['log', 'smtp']);
         });
 
+        $v->sometimes(['env.mail_username'], 'required', function($input) {
+            return !in_array($input->env['mail_username'], ['sendmail']);
+        });
+
         if ($v->passes()) {
             return Response::json(['status' => 1]);
         }