title: Setting a default queue for ActionMailer deliver_later?
body: <p>You can specify which queue to use when calling deliver_later in an ActionMailer by adding :queue as optional argument, e.g.:</p>
  
  <p><code>Notifier.welcome(User.first.id).deliver_later(queue: "low")</code></p>
  
  <p>Is there a way to do this in a general way, for all ActionMailers? To set the default ActionMailer queue?</p>