Enabling Rails 4.1 mail previews in staging (or any other env besides development)

staging.rb

# put this in your staging.rb file. Obviously you'll need more config than this it's just an example.

Rails.application.configure do
  config.action_mailer.preview_path ||= defined?(Rails.root) ? "#{Rails.root}/test/mailers/previews" : nil
  config.autoload_paths += [config.action_mailer.preview_path]

  routes.append do
    get '/rails/mailers'         => "rails/mailers#index"
    get '/rails/mailers/*path'   => "rails/mailers#preview"
  end
end

# assuming you've configured your mail previews in your test folder this will work fine

I spoke too soon. The methods defined in ApplicationController are not available in Rails::MailersController, but the methods from devise (current_user) are available here (thanks to https://gist.github.com/gabeodess/46d8e0dfcd8960defc4f for hinting me in the right direction).