For example you NEED to excempt New Signups and Lost Password requests/emails from the queue. Any queue.

And you can't do that with that plugin you suggest, while GD Mail Queue offers all that with a snippet.

GD Mail Queue is much much more advanced.

The snippet i mentioned:

add_filter('gdmaq_mailer_add_to_queue', 'custom__gdmaq_mailer_add_to_queue', 10, 3);
function custom__gdmaq_mailer_add_to_queue($add, $email, $type) {
  $dont_add = array('wp_password_change_notification', 'wp_new_user_notification_admin', 'wp_email_change_confirmation', 'wp_new_user_notification', 'wp_recovery_mode_email', 'wp_retrieve_password_message');
  if (in_array($type, $dont_add)) {
    $add = false;
  }
  return $add;
}

Also it depends on how you send your email? Directly from Wordpress? Queued to your provider email server? How many emails per queue? Lot of thing to tune.

And why a plugin for wpForo could work better? Why discover the wheel again?

With your logic, wpForo should make a plugin also for Firewall, for spam, for login protection. Not possible.

If you have a so big forum and site, invest to a better hosting plan and use some third party email service.

Email out (smtp) is handled by Wordpress not wpForo.

Use this:

https://wordpress.org/plugins/gd-mail-queue/

https://wpforo.com/community/postid/57850/ has some info on queueing mail, and I'm hoping this is going to be rolled out soon.