How to send multiple emails in Total.js at once?

function newsletter(callback, page) {

    // Example uses PostgreSQL/MySQL/SQLServer/MongoDB database with SQL Agent module
    var sql = DB();

    if (!page)
        page = 1;

    sql.select('users', 'tbl_user').make(function(filter) {
        // Reads 100 users per page
        filter.page(page, 100);
        filter.where('newsletter', true);
        filter.fields('firstname', 'email');
    });

    sql.exec(function(err, response) {

        // No users === end
        if (!response.users.length)
            return callback();

        // Sends 15 emails together
        response.users.limit(15, function(users, next) {

            var messages = [];

            for (var i = 0, length = users.length; i < length; i++) {
                var user = users[i];
                var message = Mail.create('Our new newsletter', F.view('mails/newsletter', user));
                message.to(user.email);
                message.from('info@totaljs.com', 'Total.js framework');

                // Adds the message to pending list
                messages.push(message);
            }

            // The method below sends multiple email messages in the single connection
            Mail.send2(messages, function(err, count) {
                // Next 15 emails
                next();
            });

        }, () => newsletter(callback, page + 1)); // processes next page

    });
}

// Creates a scheduler
F.schedule('09:00', '1 week', () => newsletter(NOOP));