Using previous_changes after after_save, in after_commit. Taken from http://logicalfriday.com/2012/08/21/rails-callbacks-workers-and-the-race-you-never-expected-to-lose/: Available on every object is a method called previous_changes which contains a hash of attributes that changed the last time the object was saved. Sadly, with this we don’t get…

previous_changes.rb

class User < ActiveRecord::Base

  after_commit :update_external_email, :if => :email_previously_changed?

  private

  def update_external_email
    # do whatever you need to do
  end

  def email_previously_changed?
    previous_changes[:keys].include?('email')
  end
end