diff --git a/mail-server/rmilter.nix b/mail-server/rmilter.nix
index 2372318..ed2d019 100644
--- a/mail-server/rmilter.nix
+++ b/mail-server/rmilter.nix
@@ -40,6 +40,7 @@ let
               };
               sign_alg = sha256;
               auth_only = yes;
+              header_canon = relaxed;
             }
          ''
          else "";