Fix integration between ma1sd and exim-relay

Regression since ba0a4e864a

group_vars/matrix_servers

@@ -2676,9 +2676,9 @@ matrix_ma1sd_dns_overwrite_homeserver_client_name: "{{ matrix_server_fqn_matrix
 # but may be inaccurate if matrix-corporal is enabled.
 matrix_ma1sd_dns_overwrite_homeserver_client_value: "{{ matrix_homeserver_container_url }}"
 
-# By default, we send mail through the `matrix-mailer` service.
+# By default, we send mail through the exim relay service.
 matrix_ma1sd_threepid_medium_email_identity_from: "{{ exim_relay_sender_address }}"
-matrix_ma1sd_threepid_medium_email_connectors_smtp_host: "matrix-mailer"
+matrix_ma1sd_threepid_medium_email_connectors_smtp_host: "{{ exim_relay_identifier }}"
 matrix_ma1sd_threepid_medium_email_connectors_smtp_port: 8025
 matrix_ma1sd_threepid_medium_email_connectors_smtp_tls: 0