How to set up mailer in Rails app for production environment on Heroku

I need to use a mailer for sending out emails to users to set their passwords to the "recoverable" function of Devise and active admin. On the development environment I have done this by adding the following to these files:

config/environments/development

#Added per active admin install instructions
config.action_mailer.default_url_options = { :host => 'localhost:3000' }


#These settings are for the sending out email for active admin and consequently the   devise mailer
ActionMailer::Base.delivery_method = :smtp
ActionMailer::Base.perform_deliveries = true
ActionMailer::Base.raise_delivery_errors = true
ActionMailer::Base.smtp_settings = 
{

  :address            => 'smtp.gmail.com',
  :port               => 587,
  :domain             => 'gmail.com', #you can also use google.com
  :authentication     => :plain,
  :user_name          => 'XXXXX@gmail.com',
  :password           => 'XXXXXXX'
}

How do I get the same functionality for the production environment? I want to deploy my app to Heroku. What files and code would I need to add?