When using Wordpress wp_mail()
function, there is no easy way to schedule retries, when the email fails to be sent.
There is probably a few plugins available that could handle this, but I didn't find any that would just do that.
And so, I decided to code it myself.
Of note: I added this code to a custom (unpublished) plugin I maintain. If you don't have your own plugin to add this to, either Google how to create your own Wordpress plugin, or use one of the numerous available plugins that allows you to inject (PHP) code in your Wordpress installation. As a last resort, you could add this code in your functions.php
How to catch failed emails