WP Mail force SMTP on send error

wp-mail-force-smtp.php

<?php
/**
 * Force WP_Mail with SMTP
 * Dependency : https://github.com/rohmann/global-smtp
 */
function WPMailOnSendFail($wp_error){
    $GlobalSMTP = false;

    if( file_exists( dirname(__FILE__).'/global-smtp.php' ) ){
        include_once( dirname(__FILE__).'/global-smtp.php' );
        Global_SMTP_Mailer::launch();

        // If Global SMTP is activated and configurated
        if((defined('GLOBAL_SMTP_HOST') || defined('GLOBAL_SMTP_USER') || defined('GLOBAL_SMTP_PASSWORD')) && GLOBAL_SMTP_DISABLE !== true){
            $GlobalSMTP = true;
        }
    }

    $mail_meta = $wp_error->get_error_data();

    $user_email = $mail_meta['to'];
    $subject = $mail_meta['subject'];
    $message = $mail_meta['message'];
    $message_headers = $mail_meta['headers'];
    $attachments = $mail_meta['attachments'];

    // Try a new send with wp_mail and Global SMTP
    if( $GlobalSMTP ){
        $wp_mail = wp_mail($user_email, $subject, $message, $message_headers);
    }
    
    // If wp_mail fail again or no Global SMTP installed, try to send with php mail()
    // Not the best way and can be SPAM 
    if(!$GlobalSMTP || !$wp_mail) {
        $user_email_string = '';
        for ($i=0; $i <= count($user_email) ; $i++) {
            $user_email_string .= $user_email[i].',';
        }
        mail($user_email_string, $subject, $message, $message_headers);
    }

}
add_action( 'wp_mail_failed', 'WPMailOnSendFail', 1, 10 );

?>