diff --git a/nixos/modules/services/mail/postfix.nix b/nixos/modules/services/mail/postfix.nix
index d01734d61e87..852340c05aa7 100644
--- a/nixos/modules/services/mail/postfix.nix
+++ b/nixos/modules/services/mail/postfix.nix
@@ -809,7 +809,7 @@ in
       // optionalAttrs (cfg.relayHost != "") { relayhost = if cfg.lookupMX
                                                            then "${cfg.relayHost}:${toString cfg.relayPort}"
                                                            else "[${cfg.relayHost}]:${toString cfg.relayPort}"; }
-      // optionalAttrs config.networking.enableIPv6 { inet_protocols = mkDefault "all"; }
+      // optionalAttrs (!config.networking.enableIPv6) { inet_protocols = mkDefault "ipv4"; }
       // optionalAttrs (cfg.networks != null) { mynetworks = cfg.networks; }
       // optionalAttrs (cfg.networksStyle != "") { mynetworks_style = cfg.networksStyle; }
       // optionalAttrs (cfg.hostname != "") { myhostname = cfg.hostname; }