Be careful!

The plugin sending spam through your site SMTP configuration.

Add this code to function.php for replace the plugin:

add_action( 'phpmailer_init', function ( $phpmailer ) {
    $phpmailer->isSMTP();
    $phpmailer->Host       = $SMTP_HOST; // String, ex: 'smtp.example.com'
    $phpmailer->SMTPAuth   = $SMTP_AUTH; // Boolean, ex: true
    $phpmailer->Port       = $SMTP_PORT; // String, ex: '465'
    $phpmailer->SMTPSecure = $SMTP_SECURE; // String, ex: 'ssl'
    $phpmailer->Username   = $SMTP_USERNAME; // String, ex: '[email protected]'
    $phpmailer->Password   = $SMTP_PASSWORD; // String, ex: '#your_password'
    $phpmailer->From       = $SMTP_FROM; // String, ex: '[email protected]'
    $phpmailer->FromName   = $SMTP_FROMNAME; // String, ex: "Admin"
});