Simply make Mailer.deliver_xxx_email(args) dispatch to delayed job to send, but still generate the mail content locally.

ActionMailer mail with DelayedJob.rb

class DelayedJobMailer

  def self.apply!
    
    ActionMailer::Base.class_eval do
      
      class << self  
        
        def method_missing_with_delayed_job_mailer(name, *args)   
                   
          # If we are calling the Mailer.deliver_(mail_name) method, we want to catch that and
          # convert it to a create_(mail) to create the email content. Then we call the deliver component
          # via DelayedJob:  Mailer.deliver(email)   
          
          if name.to_s =~ /^deliver_/   
            email = self.send(name.to_s.sub("deliver", "create"), *args)         
            self.send_later(:deliver, email)
          else
            method_missing_without_delayed_job_mailer(name, *args)
          end
        end    
        
        alias_method_chain :method_missing, :delayed_job_mailer       
                                                                       
      end
    end    
    
  end   

end