diff --git a/nixbld-etc-nixos/configuration.nix b/nixbld-etc-nixos/configuration.nix
index 758665d..45c267e 100644
--- a/nixbld-etc-nixos/configuration.nix
+++ b/nixbld-etc-nixos/configuration.nix
@@ -1260,14 +1260,14 @@ in
     };
   };
 
-  services.postfix.mapFiles.sender_relay = pkgs.writeText "sender_relay" ''
-      m-labs-intl.com smtptun:
+  services.postfix.mapFiles.sender_transport = pkgs.writeText "sender_transport" ''
+      @m-labs-intl.com smtptun:
       * :
   '';
   systemd.services.postfix-rebuild-sender-relay = {
-      description = "Postfix Rebuild Sender Dependent Relayhost Maps";
+      description = "Postfix Rebuild Sender Dependent Transport Maps";
       serviceConfig = {
-        ExecStart = "${pkgs.postfix}/sbin/postmap /var/lib/postfix/conf/sender_relay";
+        ExecStart = "${pkgs.postfix}/sbin/postmap /var/lib/postfix/conf/sender_transport";
       };
       wantedBy = [ "multi-user.target" ];
   };
@@ -1283,12 +1283,16 @@ in
   } // (import /etc/nixos/secret/email_settings.nix);
   services.postfix = {
     config = {
-      sender_dependent_relayhost_maps = "hash:/var/lib/postfix/conf/sender_relay";
+      sender_dependent_default_transport_maps = "hash:/var/lib/postfix/conf/sender_transport";
     };
     masterConfig."smtptun" = {
       type = "unix";
       command = "smtp";
-      args = [ "-o" "smtp_bind_address=10.47.3.2" ];
+      args = [
+        "-o" "smtp_bind_address=10.47.3.2"
+        "-o" "inet_interfaces=10.47.3.2"
+        "-o" "inet_protocols=ipv4"
+       ];
     };
   };