My rails mail initializer file.

mail.rb

ActionMailer::Base.smtp_settings = {
  :address              => ENV['SMTP_ADDRESS'],
  :port                 => ENV['SMTP_PORT'],
  :domain               => ENV['SMTP_DOMAIN'],    
  :user_name            => ENV['SMTP_USERNAME'],  #username@domain.com for google apps accounts
  :password             => ENV['SMTP_PASSWORD'],
  :authentication       => "plain",
  :enable_starttls_auto =>  true
}