This plugin enhances the security and stability of your WordPress installation by delaying and controlling wp_mail() email submissions through a managed queue.
If your site exhibits unusual behavior, such as a spam bot repeatedly submitting forms, you will be alerted immediately and can optionally pause delivery automatically while you investigate.
<ul>
<li>Intercepts wp_mail() and places outgoing messages in a queue</li>
<li>Configure how many emails are sent and at what interval</li>
<li>Pause the queue without disabling the plugin completely</li>
<li>Log queued emails, sent emails, alerts, and queue events</li>
<li>Receive alerts when the queue grows unexpectedly</li>
<li>Optionally auto-pause the queue when an alert is triggered</li>
<li>Send selected queued emails immediately from the backend</li>
<li>Automatically prioritize WordPress password reset emails</li>
<li>Receive alerts when WordPress is unable to send emails</li>
</ul>

Mail Queue

Gain full control over your WordPress emails. Queue outgoing emails and get alerts when your site tries to send unusually high volumes.

shawfactor

If you are sending large volumes of emails this is the plugin you need.
Generally wordpress emails are best sent by a third party, like gmauil or Sendgrid. But connecting and sending a large number of emails to third parties will slow your visitor experience down.
Unless those emails are sent in the background. This plugin does that.

LH Email Queue and Log

LH Email enables you to queu your emails so they are sent asynchronously.

Mail Queue vs LH Email Queue and Log