+## DKIM headers list.
+## Surprise! Internal whitespace isn't allowed here.
+DEFCONF(dkim_headers,m4_dnl
+References:In-Reply-To:Subject:To:Date:Message-ID:m4_dnl
+From:Sender:Reply-To:Cc:m4_dnl
+Content-Transfer-Encoding:Content-Type:MIME-Version:m4_dnl
+Content-ID:Content-Description)
+
+## TLS certificate list.
+DEFCONF(certlist,
+<:m4_ifelse(t, m4_ifelse(MODE, hub, nil, MODE, srv, nil, t),
+<:CONF_sysconf_dir/server.certlist:>,
+<:CONF_sysconf_dir/${if ={$received_port}{CONF_submission_port}{server}\
+ {${if match_ip{$sender_host_address}{+trusted} \
+ {server}{letsencrypt}}}}.certlist:>):>)
+