The JavaMail page on the Oracle website describes it as follows
The JavaMail API provides a platform-independent and protocol-independent framework to build mail and messaging applications. The JavaMail API is available as an optional package for use with the Java SE platform and is also included in the Java EE platform.
The primary site for the JavaMail project is now on java.net. From there you can find the javadocs for many versions of the APIs, links to the source code repositories, links for downloads, examples and hints for using JavaMail with some popular Email service providers.