Add email-sending support

roles/matrix-server/templates/systemd/matrix-mailer.service.j2

@@ -0,0 +1,20 @@
+[Unit]
+Description=Matrix mailer
+After=docker.service
+Requires=docker.service
+
+[Service]
+Type=simple
+ExecStartPre=-/usr/bin/docker kill matrix-mailer
+ExecStartPre=-/usr/bin/docker rm matrix-mailer
+ExecStart=/usr/bin/docker run --rm --name matrix-mailer \
+			--network={{ matrix_docker_network }} \
+			--env-file={{ matrix_environment_variables_data_path }}/env-mailer \
+			{{ matrix_docker_image_mailer }}
+ExecStop=-/usr/bin/docker kill matrix-mailer
+ExecStop=-/usr/bin/docker rm matrix-mailer
+Restart=always
+RestartSec=30
+
+[Install]
+WantedBy=multi-user.target

roles/matrix-server/templates/systemd/matrix-synapse.service.j2

@@ -10,6 +10,9 @@ After=matrix-postgres.service
 After=matrix-goofys.service
 Requires=matrix-goofys.service
 {% endif %}
+{% if matrix_mailer_enabled %}
+Wants=matrix-mailer.service
+{% endif %}
 Wants=matrix-coturn.service
 
 [Service]