We use the WordPress wp_mail() function to trigger the emails, after that it's up to your mail server to handle them. You'll want to make sure you're receiving any emails from WordPress, then contact your host. They can run a traceroute to find out what's happening to them.
Welcome to the iThemes Help Center. The purpose of this center is to be a central repository for documentation and tutorials for our themes and plugins.
You can add the code below into the wp-config.php file anywhere as long as it is between the first line ( <?php ) and the line that says / That's all, stop editing. Happy Blogging / to temporarily disable all features so you can log in. If needed, you can see how to edit the wp-config.php file in this article.
Until you've resolved the email issue you should switch to the more reliable and secure app-based TOTP method, and generate backup codes in case service isn't available.