Sendgrid usage

configuration.rb

module Sendgrid
  module Configuration

    def self.included(klass)
      klass.extend ClassMethods
    end

    def mail(headers = {}, &block)
      headers['X-SMTPAPI'] = { category: calling_mailer_and_action.join("#") }.to_json
      super(headers, &block)
    end

  protected

    # Returns e.g. [ "FooMailer", "my_action" ]
    #
    # Thank you Joakim Kolsjö and Henrik Nyh! https://gist.github.com/2775581
    def calling_mailer_and_action
      # The caller method gives the call chain in the format
      #   [ "app_mailer.rb:2 in `my_method'", "sub_mailer.rb:5 in `my_method'", script/rails:6 in `<main>"' ]
      # Look for Mailer classes and pick the last one, at the bottom of the inheritance chain.
      if caller_string = caller.grep(%r{/app/mailers/.+_mailer\.rb}).last
        # Extract mailer name and action from that line.
        mailer, action = caller_string.scan(%r{/app/mailers/(.+_mailer)\.rb:\d+:in `(.+)'}).flatten
        [ mailer.camelize, action ]
      end
    end

    module ClassMethods
      # Makes it possible to use a different sendgrid account for a mailer
      def sendgrid_credentials(username, password)
        @sendgrid_username = username
        @sendgrid_password = password
      end

      def delivery_method
        use_sendgrid? ? :smtp : :test
      end

      def smtp_settings
        {
          :address => "smtp.sendgrid.net",
          :port => 587,
          :enable_starttls_auto => true,
          :user_name => @sendgrid_username,
          :password => @sendgrid_password
        }
      end

    protected

      def use_sendgrid?
        @sendgrid_username.present? && @sendgrid_password.present?
      end
    end

  end
end

payment_mailer.rb

require 'sendgrid/configuration'

class PaymentMailer < ActionMailer::Base
  include Sendgrid::Configuration
  sendgrid_credentials AppConfig.sendgrid.username, AppConfig.sendgrid.password

  default :from => '"Mynewsdesk" <[email protected]>'

  def payment_success(user, payment)
    @payment = payment
    I18n.with_locale(user.locale) do
      mail({
        :subject => I18n.t(:'mailer.payment_success.payment_success'),
        :to => user.email
      })
    end
  end
end