Auto-bcc'ing emails sent from Devise.

While digging through the Devise source some time back, I found a little known and undocumented feature that offers some great flexibility: you can define the parent class for the DeviseController and DeviseMailer. Devise uses sane defaults and so these classes inherit from ApplicationController and ActionMailer::Base respectively. These are defined as module accessors, on the Devise module. Devise uses this configuration when defining the DeviseMailer:

class Devise::Mailer < Devise.parent_mailer.constantize
  include Devise::Mailers::Helpers

  # there's more stuff in here, you should read the source!

Why is this useful? There are times when it’s convenient to be able to change this class. For instance, let’s suppose we want to automatically bcc an email address on new emails delivered from Devise. I needed to do this recently and found it to be quite easy using the parent_mailer configuration.

First, create a new mailer class that inherits from ActionMailer::Base and put it in app/mailers, let’s call it BaseMailer. The simplest example would be an empty class:

class BaseMailer < ActionMailer::Base

Then, in the initializer (typically config/initializers/devise.rb), instruct Devise to use this class as the parent_mailer:

Devise.setup do |config|
  config.parent_mailer = 'BaseMailer'

For the sake of brevity, I’ve omitted the rest of the Devise configuration, but you’ll want to add the parent_mailer alongside any other configuration items. Now DeviseMailer will inherit from our mailer class. Now, it’s just a matter of hooking in our auto-bcc logic:

class BaseMailer < ActionMailer::Base


  def mail_with_bcc(headers={}, &block)
    headers.merge!(:bcc => '')
    mail_without_bcc(headers, &block)
  alias_method_chain :mail, :bcc

As you can tell, I really enjoy reading other people’s code. Especially when you are pleasantly surprised by a feature that solves a problem you are trying to solve!