matrix-docker-ansible-deploy/roles/matrix-server/templates/env/env-mailer.j2

MAILNAME={{ hostname_matrix }}
{% if matrix_mailer_relay_use %}
RELAYHOST={{ matrix_mailer_relay_host_name }}:{{ matrix_mailer_relay_host_port }}
{% endif %}
{% if matrix_mailer_relay_auth %}
RELAYHOST_AUTH=yes
RELAYHOST_PASSWORDMAP={{ matrix_mailer_relay_host_name }}:{{ matrix_mailer_relay_auth_username }}:{{ matrix_mailer_relay_auth_password }}
{% endif %}