Failed sending Security Digest notification

Hi all,

I’m getting a notification error when iThemes Security tries sending a notification e-mail:

Invalid address: (From): SMTP_FROM (wp_mail_failed)
Module - Notification Center
Description - Sending Security Digest Failed

Instead of using a plugin like WP Mail SMTP, I’m using my own code in functions.php for SMTP settings:

function smtp($phpmailer) {
    if(!is_object($phpmailer))
        $phpmailer = (object) $phpmailer;

    $phpmailer->isSMTP();
    $phpmailer->Host = SMTP_SERVER;
    $phpmailer->Port = SMTP_PORT; 
    $phpmailer->Username = SMTP_USERNAME;
    $phpmailer->Password = SMTP_PASSWORD;
    $phpmailer->SMTPAuth = SMTP_AUTH;
    $phpmailer->SMTPSecure = SMTP_SECURE;
    $phpmailer->From = SMTP_FROM;
    $phpmailer->FromName = SMTP_NAME;
}
add_action('phpmailer_init', 'smtp');

SMTP_FROM comes from wp-config.php file with e.g. define('SMTP_FROM', '[email protected]');. Everything else mail-wise is working on my site, seems like iThemes Security isn’t, for some reason, fetching the variable.

Any clues?