Setting SendGrid category to ActionMailer mailer and action in Rails 3.

application_mailer.rb

# By Joakim Kolsjö and Henrik Nyh of Barsoom AB. MIT license.

class ApplicationMailer < ActionMailer::Base

  def custom_mail(options)
    text = options.delete(:text)

    add_sendgrid_headers

    mail(options) do |format|
      format.text { render(text: text) }
    end
  end

  # Set headers for SendGrid statistics: http://sendgrid.com/
  def add_sendgrid_headers
    mailer, action = calling_mailer_and_action
    headers "X-SMTPAPI" => "{ \"category\": \"#{mailer}##{action}\" }"
  end

  # Returns e.g. [ "FooMailer", "my_action" ]
  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

end

example_mailer.rb

class ExampleMailer < ApplicationMailer

  def bar(customer)
    custom_mail(
      to:      customer.email,
      subject: t(:'mailers.example.bar.subject'),
      text:    t(:'mailers.example.bar.body')
    )
  end

end

See this blog post for a nicer implementation.

Updated URL http://thepugautomatic.com/2012/08/sendgrid-metadata-and-rails/