diff --git a/config/hosts/mail-1/simple-nixos-mailserver.nix b/config/hosts/mail-1/simple-nixos-mailserver.nix
index 0f8d76f..9bcbe46 100644
--- a/config/hosts/mail-1/simple-nixos-mailserver.nix
+++ b/config/hosts/mail-1/simple-nixos-mailserver.nix
@@ -75,8 +75,8 @@
 
   services.postfix = {
     transport = "relay:[mail-2.grzb.de]";
-    extraConfig = ''
-      proxy_interfaces = 212.53.203.19
-    '';
+    settings.main = {
+      proxy_interfaces = "212.53.203.19";
+    };
   };
 }