Error: too many emails per second on Heroku
<p>I have rails 4 app on Heroku sending emails via <code>deliver_later</code>. Sidekiq is running and working and I have <code>config.active_job.queue_adapter = :sidekiq</code> in my config.</p>

<p>I also see this in the logs <code>[ActiveJob] [ActionMailer::DeliveryJob]</code> which makes me believe emails are being sent as background jobs.</p>

<p><strong>So why do I still get errors about too many emails per second?</strong>  </p>

<blockquote>
  <p>Net::SMTPUnknownError: could not get 3xx (550: 550 5.7.0 Requested action not taken: too many emails per second</p>
</blockquote>

<p>I just noticed I have sidekiq concurrency set to 3. Maybe that's the problem?</p>