diff --git a/rmilter/rmilter.conf b/rmilter/rmilter.conf
index 8bba80f2..991adf9b 100644
--- a/rmilter/rmilter.conf
+++ b/rmilter/rmilter.conf
@@ -124,7 +124,8 @@ dkim {
   header_canon = relaxed;
   body_canon = relaxed;
   sign_alg = sha256;
-  auth_only = no;
+  auth_only = yes;
+  sign_networks = 127.0.0.1, 192.168.0.0/16, 172.16.0.0/12, 10.0.0.0/8, [::1]/128;
 };
 
 # .try_include /overrides/rmilter.conf