JavaBeans Activation Framework
Regardless of which JavaMail API version you use, they all require the JavaBeans Activation Framework (JAF) standard extension, which is now included in WebLogic Server 8.1 (javax.activation). The JAF gives your email applications the capability to recognize, display, and/or manipulate various types of MIME data, such as HTML pages and JPEG files. You don't really need to know how the API works because it's auto-enabled by the JavaMail API, but here are a few of the high-level details.
The framework provides classes that add MIME-type support to your applications. This is done by determining the type of an arbitrary piece of data, encapsulating access to it, discovering the operations available on it, and instantiating the appropriate bean to perform operations on it. For example, if an email application receives a message containing a JPEG image, the JAF enables the email application to identify that stream of data as an JPEG image, and from that type, the application can locate and instantiate an object that can manipulate or view that image.