application.rb

    if ENV['SMTP_HOST'].present?
      config.action_mailer.delivery_method = :smtp
      config.action_mailer.smtp_settings = {
        :address        => ENV['SMTP_HOST'],
        :port           => ENV['SMTP_PORT'],
        :authentication => ENV['SMTP_AUTH'].to_sym,
        :user_name      => ENV['SMTP_USERNAME'],
        :password       => ENV['SMTP_PASSWORD'],
        :domain         => ENV['SMTP_DOMAIN'],
        :enable_starttls_auto => (ENV['SMTP_TLS'] == 'true')
      }
    elsif !Rails.env.development?
      config.action_mailer.delivery_method = :sendmail
    end