diff --git a/core/admin/mailu/internal/nginx.py b/core/admin/mailu/internal/nginx.py
index 420fe252..1a62f795 100644
--- a/core/admin/mailu/internal/nginx.py
+++ b/core/admin/mailu/internal/nginx.py
@@ -25,6 +25,7 @@ STATUSES = {
         "smtp": "451 4.3.2",
         "submission": "451 4.3.2",
         "pop3": "-ERR [LOGIN-DELAY] Retry later"
+        "sieve": "AuthFailed"
     }),
 }