Add DKIM to sending via smarthost.

No idea why Debian doesn't have this enabled.

states/email/exim4/conf.d/transport/30_exim4-config_remote_smtp_smarthost

@@ -0,0 +1,78 @@
+
+### transport/30_exim4-config_remote_smtp_smarthost
+#################################
+
+# This transport is used for delivering messages over SMTP connections
+# to a smarthost. The local host tries to authenticate.
+# This transport is used for smarthost and satellite configurations.
+# Refuse to send any messsage with over-long lines, which could have
+# been received other than via SMTP. The use of message_size_limit to
+# enforce this is a red herring.
+
+remote_smtp_smarthost:
+  debug_print = "T: remote_smtp_smarthost for $local_part@$domain"
+  driver = smtp
+  multi_domain
+.ifndef IGNORE_SMTP_LINE_LENGTH_LIMIT
+  message_size_limit = ${if > {$max_received_linelength}{998} {1}{0}}
+.endif
+  hosts_try_auth = <; ${if exists{CONFDIR/passwd.client} \
+        {\
+        ${lookup{$host}nwildlsearch{CONFDIR/passwd.client}{$host_address}}\
+        }\
+        {} \
+      }
+.ifdef REMOTE_SMTP_SMARTHOST_HOSTS_AVOID_TLS
+  hosts_avoid_tls = REMOTE_SMTP_SMARTHOST_HOSTS_AVOID_TLS
+.endif
+.ifdef REMOTE_SMTP_SMARTHOST_HOSTS_REQUIRE_TLS
+  hosts_require_tls = REMOTE_SMTP_SMARTHOST_HOSTS_REQUIRE_TLS
+.endif
+.ifdef REMOTE_SMTP_SMARTHOST_TLS_VERIFY_CERTIFICATES
+  tls_verify_certificates = REMOTE_SMTP_SMARTHOST_TLS_VERIFY_CERTIFICATES
+.endif
+.ifdef REMOTE_SMTP_SMARTHOST_TLS_VERIFY_HOSTS
+  tls_verify_hosts = REMOTE_SMTP_SMARTHOST_TLS_VERIFY_HOSTS
+.endif
+.ifdef REMOTE_SMTP_HEADERS_REWRITE
+  headers_rewrite = REMOTE_SMTP_HEADERS_REWRITE
+.endif
+.ifdef REMOTE_SMTP_RETURN_PATH
+  return_path = REMOTE_SMTP_RETURN_PATH
+.endif
+.ifdef REMOTE_SMTP_HELO_DATA
+  helo_data=REMOTE_SMTP_HELO_DATA
+.endif
+.ifdef DKIM_DOMAIN
+dkim_domain = DKIM_DOMAIN
+.endif
+.ifdef DKIM_SELECTOR
+dkim_selector = DKIM_SELECTOR
+.endif
+.ifdef DKIM_PRIVATE_KEY
+dkim_private_key = DKIM_PRIVATE_KEY
+.endif
+.ifdef DKIM_CANON
+dkim_canon = DKIM_CANON
+.endif
+.ifdef DKIM_STRICT
+dkim_strict = DKIM_STRICT
+.endif
+.ifdef DKIM_SIGN_HEADERS
+dkim_sign_headers = DKIM_SIGN_HEADERS
+.endif
+.ifdef DKIM_TIMESTAMPS
+dkim_timestamps = DKIM_TIMESTAMPS
+.endif
+.ifdef TLS_DH_MIN_BITS
+tls_dh_min_bits = TLS_DH_MIN_BITS
+.endif
+.ifdef REMOTE_SMTP_SMARTHOST_TLS_CERTIFICATE
+tls_certificate = REMOTE_SMTP_SMARTHOST_TLS_CERTIFICATE
+.endif
+.ifdef REMOTE_SMTP_SMARTHOST_PRIVATEKEY
+tls_privatekey = REMOTE_SMTP_SMARTHOST_PRIVATEKEY
+.endif
+.ifdef REMOTE_SMTP_TRANSPORTS_HEADERS_REMOVE
+  headers_remove = REMOTE_SMTP_TRANSPORTS_HEADERS_REMOVE
+.endif