Proper exception handling in Rails 3

gistfile1.rb

# coding: utf-8
class ApplicationController < ActionController::Base
  protect_from_forgery
  rescue_from Exception, :with => :handle_exceptions

private

  def handle_exceptions(e)
    case e
    when CanCan::AccessDenied
      authenticate_user!
    when ActiveRecord::RecordNotFound
      not_found
    else
      internal_error(e)
    end
  end

  def not_found
    # Just render view
    render 'application/not_found', :status => 404
  end

  def internal_error(exception)
    if RAILS_ENV == 'production'
      # Send message to admin email via exception_notification
      request.env['exception_notifier.options'] = {
        :sender_address       => "sender@example.com",
        :exception_recipients => "recipient@example.com"
      }

      ExceptionNotifier::Notifier.exception_notification(request.env, exception).deliver

      # And just render view
      render :layout   => 'layouts/internal_error',
              :template => 'application/internal_error',
              :status   => 500
    else
      throw exception
    end
  end
end

great explanation!