wp_mail_failed

// define the wp_mail_failed callback function action_wp_mail_failed($wp_error) { return error_log(print_r($wp_error, true)); } // add the action add_action(‘wp_mail_failed’, ‘action_wp_mail_failed’, 10, 1); I personally use slack’s webhooks and other methods for this notification. Reference: https://www.codeforest.net/debugging-wp-mail-like-a-boss-debugger