This will turn on deferred transactional emails in WooCommerce. This may help if you are experiencing slow checkouts or checkout timeouts.

woocommerce_defer_transactional_emails.php

<?php // Do not copy this line

/**
 * This will turn on deferred transactional emails in WooCommerce. This may help if you 
 * are experiencing slow checkouts or checkout timeouts. 
 */
add_filter( 'woocommerce_defer_transactional_emails', '__return_true' );

May i know this code will defer the email to how many seconds? Minutes?

@dzulhelmi it will depend on the site itself, but it shouldn't be more than a couple minutes. What this does is instead of sending emails during the checkout process, it puts them into a queue. The queue is scheduled to send in 10 seconds, but it's based on WP Cron, which depends on traffic to the site. If there's active traffic, it should only be a few seconds, but it could take a few minutes. It also depends on the hosting, if emails are slow to send on the host, it could take longer, which is why someone would use this filter in the first place.

It is not based on WP Cron, it uses an async queue, this one: https://github.com/deliciousbrains/wp-background-processing

What it does is basically just before PHP would shut down, it fires a remote request to the site itself without waiting for the response. The request triggers another PHP process in which the queued actions are performed. So the emails deferred this way are sent almost instantly, but they are sent in a different request, independent of the actual one, therefore any issues or waiting for SMTP server, etc cannot slow down the response to the main request.