+DEFCONF(relay_clients, <m4_dnl
+; +trusted m4_dnl
+; 172.31.80.8 m4_dnl chiark (VPN)
+; 172.29.198.161 ; 2001:8b0:c92:a000::1:1 m4_dnl national
+)
+
+## DKIM headers list.
+DEFCONF(dkim_headers, m4_dnl
+References : In-Reply-To : Subject : To : Date : Message-ID : m4_dnl
+From : Sender : Reply-To : Cc : m4_dnl
+Resent-Date : Resent-From : Resent-Sender : Resent-To : Resent-Cc : m4_dnl
+Resent-Message-ID : m4_dnl
+Content-Transfer-Encoding : Content-Type : MIME-Version : m4_dnl
+Content-ID : Content-Description : m4_dnl
+List-Id : List-Help : List-Unsubscribe : List-Subscribe : m4_dnl
+List-Post : List-Owner : List-Archive m4_dnl
+)
+
+## 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:>):>)