CComponent | --YiiMailMessage
Located in File: /YiiMailMessage.php
This means you need to look at the Swift Mailer documentation to see what methods are availiable for this class. There are a lot of methods, more than I wish to document. Any methods availiable in Swift_Mime_Message are availiable here.
Documentation for the most important methods can be found at http://swiftmailer.org/docs/messages
The YiiMailMessage component also allows using a shorthand for methods in Swift_Mime_Message that start with set* or get* For instance, instead of calling $message->setFrom('...') you can use $message->from = '...'.
Here are a few methods to get you started: