diff --git a/share/wildduck/zonemta.tf b/share/wildduck/zonemta.tf
index 9323c1a..d355774 100644
--- a/share/wildduck/zonemta.tf
+++ b/share/wildduck/zonemta.tf
@@ -168,7 +168,7 @@ resource "kubernetes_config_map_v1" "zonemta_config" {
             cipher="aes192"
             secret="${local.secrets.dkim}"
             useOpenSSL=true
-            signTransportDomain=false
+            signTransportDomain=true
             hashAlgo="sha256"
   EOF
   )