Apostle provides a nifty facility for sending app-generated, transactional emails from your application including Wordpress-like mail formatting and full tracking (delivery, opening, clicking etc.) of all emails sent. No need to set up email facilities on your app server!
This tutorial describes how to connect to a remote service via tunnel when only most basic software is available on the remote server. It is not directly related to Yii. It could be hovewer useful for web developers working with shared hosting sites with limited access.