DKIM and ARC signing headers are duplicate

[dmagyar]

I had to override the arc.conf and dkim_signing.conf inside of /etc/rspamd/local.d/ because with the default settings it duplicated headers in the h= value upon signature.

I've added this line: sign_headers = "From:To:Cc:Reply-To:Subject:Date:Message-ID:Content-Type:MIME-Version";

Before fix:

Thu, 7 Aug 2025 18:02:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=magyar.cc; s=mail;
t=1754589735;
h=from:from:reply-to:subject:subject:date:date:message-id:message-id:to:to:cc:mime-version:mime-version:content-type:content-type:content-transfer-encoding:content-transfer-encoding;bh=3g7dCsSnBa/3DzRzTpCh0KHYt2q+S7U/Pqk0vBBbOxc=;
...

After the fix:

Thu, 7 Aug 2025 18:24:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=magyar.cc; s=mail;t=1754591090; h=From:To:Subject:Date:Message-ID:Content-Type:MIME-Version;bh=QiaZNjwFn4oYKodBLPIakUzYeLdRWb2pzG63ib7+968=;

Without this fix DKIM checks at gmail fail. Recommend incorporating this into the default conf files.

[AndrewSav]

Thank you for the report @dmagyar, could you please link to any discussion about the defaults of rspamd being inadequate, and suggesting this corrected line. If you came up with this line on your own, could you please provide the default value and explain the difference.

Thanks!