diff --git a/services/mailu/helmrelease.yaml b/services/mailu/helmrelease.yaml
index a40f047..339884b 100644
--- a/services/mailu/helmrelease.yaml
+++ b/services/mailu/helmrelease.yaml
@@ -220,6 +220,7 @@ spec:
         smtp_use_tls: "yes"
         smtp_tls_security_level: "encrypt"
         smtp_sasl_security_options: "noanonymous"
+        smtpd_relay_restrictions: "permit_sasl_authenticated, reject_unauth_destination"
     redis:
       enabled: true
       architecture: standalone