This mailbox implementation stores messages in a Java Persistence API store (think data bases, but not limited to that).
Default JPA provider is Apache OpenJPA, but you can roll your own by extending JPAMailboxManager and JPAMessageManager in the same way as OpenJPAMailboxManager and OpenJPAMessageManager do.
It only supports the Basic capability.
The JPA implementation uses Java Persistence API Annotations to map Java objects to data base tables. The current implementation also supports features such as storing messages in an encrypted database and provide on the fly encryption/decryption.