The most important thing to respect is probably this statement:
  You acknowledge that Software is not designed, licensed or intended for use in the design, construction, operation or maintenance of any nuclear facility
Seriously, here is what can be found in the FAQ:
  Q: Is the JavaMail API implementation
  completely free? Can I ship it along
  with my product?
  
  A: Yes. The current
  release of the JavaMail API
  implementation, is completely free and
  you can include it in your product.
  This release includes IMAP, POP3, and
  SMTP providers as well. Please do read
  the license and ensure that you
  understand it. (The license is
  available after clicking the Download
  button on the download page.) The
  JavaBeans Activation Framework is also
  free for use under a similar license.