If you're interested in contributing to JavaMail, please see the Contributions page on the JavaMail web site.
GitHub Repositories
You can use the code from these repositories to experiment, test, build, create patches, issue pull requests, etc.
https://github.com/jakartaee/mail-api - Project repository hosted on GitHub.
https://github.com/jakartaee/mail-tck - Project repository hosted on GitHub.
https://github.com/jakartaee/mail-spec - Project repository hosted on GitHub.