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.