title: Difference between Action Job/Mailer's `deliver_now` and `deliver_later`
body: <p>The common pattern for interfacing with <code>ActiveJob</code> in Rails is to set up a Job with a <code>perform()</code> method that gets called asynchronously via <code>perform_now</code> or <code>perform_later</code></p>
  <p>In the special case of Mailers, you can directly call <code>deliver_now</code> or <code>deliver_later</code> since <code>ActiveJob</code> is well integrated with <code>ActionMailer</code>.</p>
  <p>The <a href="http://edgeguides.rubyonrails.org/active_job_basics.html#action-mailer" rel="nofollow noreferrer">rails documentation</a> has the following comments -</p>
  <pre><code># If you want to send the email now use #deliver_now
  UserMailer.welcome(@user).deliver_now
   
  # If you want to send the email through Active Job use #deliver_later
  UserMailer.welcome(@user).deliver_later
  </code></pre>
  <p>The wording makes it seem like <code>deliver_now</code> will <em>not</em> use <code>ActiveJob</code> to send the mail. Is that correct, and if so what's the true difference between <code>deliver_now</code> and <code>deliver_later</code>? Is one not asynchronous?</p>
  <p>Similarly, does the same difference apply to <code>perform_now</code> and <code>perform_later</code> ?</p>
  <p>Thanks!</p>