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

It seems we need to include url_helpers manually.

class ::Rails::MailersController
+  include Rails.application.routes.url_helpers
  def local_request?
    true
  end
end

It seems we need to include url_helpers manually. Otherwise, the mailer preview index throws arguments passed to url_for can't be handled. Please require routes or provide your own implementation.

class ::Rails::MailersController
  include Rails.application.routes.url_helpers

  def local_request?
    true
  end
end

As of Rails 4.2 you can do all of this with a config option, obviating the need for this workaround.

Just add this to config/<environment_name).rb

  config.action_mailer.preview_path  = "#{Rails.root}/whatever"
  config.action_mailer.show_previews = true

@armchairdj Thank you!

How do you make it so it is only accessible to admin users? The authorization methods that would normally be available (from Devise in my case) are not available since Rails::MailersController is not a subclass of ApplicationController.

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).