Sample Rails ActionMailer config/initializer

smtp.rb

# this file should be config/initializers/smtp.rb

config_file = File.join(Rails.root.to_s, '/config/smtp.yml')

if File.exists? config_file
  if smtp_config = YAML.load_file(File.expand_path(config_file))[Rails.env]
    MyApp::Application.config.action_mailer.delivery_method = :smtp
    MyApp::Application.config.action_mailer.smtp_settings = smtp_config
  end
end

smtp.yml

---
development:
  :address: localhost
  :port: 1025
  :domain: foobar.dev

test:
  :address: localhost
  :port: 1025
  :domain: foobar.dev

production:
  :address: localhost
  :port: 25
  :domain: mail.example.com
  :user_name: username
  :password: password