jDKIM is a DKIM implementation library written in Java. It provides both verification and signing and also provides Mailets for the Apache JAMES project.
The 0.1 release is the first release. It requires Java 1.4 at runtime but for full compliance with the DKIM specification the JVM running the library must support SHA256withRSA cypher suite. The default Sun Java 1.4 does not support this suite, so either you move to Java 1.5+ or you install a third party cryptography provider like BouncyCastle and configure it appropriately in your JVM.
The product currently include a generic library module called "main" and a module providing mailets for DKIM signing