The 0.4 release brought a number of significant improvements in terms of supported capabilities, flexibility and performance.
The 0.5 release addressed a number of important issues discovered since the 0.4 release. In particular it improved Mime4j ability to deal with malformed data streams including those intentionally crafted to cause excessive CPU and memory utilization that can lead to DoS conditions.
The 0.6 release brought another round of API enhancements and performance optimizations. As of this release Mime4j requires a Java 1.5 compatible runtime.
The 0.7 release brings another round of API enhancements, bug fixes and performance optimizations. A major effort has been put in code reorganization, separating parsing code from DOM manipulation code. Mime4J has been restructured into three separate modules: 'core', 'dom' and 'storage'. The 'core' package provides an event-driven SAX style parser that relies on a callback mechanism to report parsing events such as the start of an entity header the start of a body, etc. The 'dom' package contains base/abstract classes and interfaces for MIME-DOM manipulation aiming to provide the base for a full featured traversable DOM. Per default the Mime4J DOM builder stores content of individual body parts in memory. The 'storage' package provides support for more complex storage backends such on-disk storage systems, overflow on max limit, or encrypted storage through JSSE API.
The next release will be version 0.8. As of this release Mime4j requires a Java 1.6 compatible runtime.