transports: tweak dkim-signed headers for mailing lists

1 files changed, 10 insertions, 9 deletions

diff --git a/conf.d/040_transports.conf b/conf.d/040_transports.conf
index 543671f..01de429 100644
--- a/conf.d/040_transports.conf
+++ b/conf.d/040_transports.conf
@@ -22,16 +22,17 @@ remote_smtp:
 
 
 # Sign outgoing mail with DKIM.
-# Only mail sent by authenticated users is signed, leaving forwarded mail untouched.
-# The "Sender" header is excluded from the signature process, allowing mailing list
-# servers to forward messages without invalidating the signature.
+# Only mail sent by authenticated users is signed, leaving forwarded mail
+# untouched.
+# The "Sender" and "List-*" headers are excluded from the signature process
+# if they are not already present, allowing mailing list servers to forward
+# messages without invalidating the signature.
+# Default _DKIM_SIGN_HEADERS:
+# https://github.com/Exim/exim/blob/042e558/src/src/pdkim/pdkim.h#L29-L36
 # ref: https://www.spinics.net/lists/linux-media/msg138870.html
+# ref: https://lists.gt.net/exim/users/110610#110610
 
-.ifdef _DKIM_SIGN_HEADERS
-DKIM_SIGN_HEADERS = _DKIM_SIGN_HEADERS
-.else
-DKIM_SIGN_HEADERS = In-Reply-To:Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID:Subject:To:From:Date:Sender:Reply-To:Cc:Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive
-.endif
+DKIM_SIGN_HEADERS = From:=Sender:Reply-To:Subject:Date:Message-ID:To:Cc:MIME-Version:Content-Type:Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:=List-Id:=List-Help:=List-Unsubscribe:=List-Subscribe:=List-Post:=List-Owner:=List-Archive
 
 DKIM_PRIVATE_KEY_FILE = DKIMDIR/$dkim_selector._domainkey.$dkim_domain.pem
 
@@ -43,7 +44,7 @@ signed_smtp:
   dkim_private_key   = ${if exists{DKIM_PRIVATE_KEY_FILE}{DKIM_PRIVATE_KEY_FILE}{0}}
   dkim_canon         = relaxed
   dkim_strict        = yes
-  dkim_sign_headers  = ${filter{DKIM_SIGN_HEADERS}{!eq{$item}{Sender}}}
+  dkim_sign_headers  = DKIM_SIGN_HEADERS
 
 
 # This transport is used for local delivery to user mailboxes in traditional