Mix and Match Namespace Styles

You can even mix and match between the inline style and the file-based style.

# settings.yml

development:
  smtp:
    username: my_development_username
    password: my_development_password`

test:
  smtp:
    username: my_test_username
    password: my_test_password`

staging:
  smtp:
    username: my_staging_username
    password: my_staging_password`

# settings-production.yml

smtp:
  username: my_production_username
  password: my_production_password`

The above will yield the results you would expect, but allows you to keep the production values in a separate file which can be secured separately. Although I would recommend keeping everything together and just encrpyting your sensitive info.