smtp_address: ":1025"
submission_address: ":1587"
submission_over_tls_address: ":1465"
mail_delivery_agent_bin: "test-mda"
mail_delivery_agent_args: "%to%"
data_dir: "../.data"
# This is expected to be invalid, and impossible to mkdir.
mail_log_path: "/sys/bad-dir/mail_log"