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

nigro.simone

Speed Up – Optimize CSS Delivery

This plugin load the stylesheets asynchronously and improve page load times.

dmikam

Async JS and CSS

Converts render-blocking CSS and JS files into NON-render-blocking, improving performance of web page.

Paris Holley

Asynchronous Javascript

Improve page load performance by asynchronously loading javascript using head.js

da.futt

Asynchronous Widgets

Asynchronous Widgets allows you to have any registered widget on your WordPress.org-powered
site be loaded asynchronously via an AJAX call.

Mahesh Thorat

AJAX Loading

This plugin improves your users page experience without reloading pages using AJAX.

kylereicks

Head.WP

Head.js is a script to asynchronously load and manage dependencies of javascript and CSS assets.

Thoog_10

Async Vid List

Lets the user create lists of video embeds that load and play asynchronously in one div

wilmveel

WP Angular

This plugin allows you to build your templates in a AngularJS way.

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.

Alternatives to LH Email Queue and Log

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