The 1.5.6 release contains 17 bug fixes but no significant enhancements.
The full list of changes is here:
https://javaee.github.io/javamail/docs/CHANGES.txt
Please note the potential compatibility issues in this release:
https://javaee.github.io/javamail/docs/COMPAT.txt
Please send feedback to javamail_ww@oracle.com.
Enjoy!
The JavaMail Team