class ActionMailer::MessageDelivery

def deliver_later(options={})

* :queue - Enqueue the email on the specified queue
* :wait_until - Enqueue the email to be delivered at (after) a specific date / time
* :wait - Enqueue the email to be delivered with a delay

Options:

Notifier.welcome(User.first).deliver_later(wait_until: 10.hours.from_now)
Notifier.welcome(User.first).deliver_later(wait: 1.hour)
Notifier.welcome(User.first).deliver_later

job runs it will send the email using +deliver_now+.
Enqueues the email to be delivered through Active Job. When the 
def deliver_later(options={})
  enqueue_delivery :deliver_now, options
end