Delay all mails in application

queued_delivery.rb

# in config/application.rb
ActionMailer::Base.add_delivery_method :queued, Mail::QueuedDelivery

# in config/environment.rb
config.action_mailer.delivery_method = :queued

# in lib/mail/queued_delivery.rb
module Mail
  class QueuedDelivery

    def initialize(values = {})
      # (optional)
    end

    def deliver!(mail)
      email = Email.create!(:delivery_handler => mail.delivery_handler.name, :message => mail.to_s)
      Delayed::Job.enqueue Jobs::Email::DeliverEmail.new(email.id)
    end

  end
end