You might try to encode using PGP first, then transmit. I've done that in Perl. If you then taking the result and store it in a file, you should be able to grab the contents and call it a message. Worth a try.
Why not use the Java Cryptography Extension (JCE) to encode the text of the email and then send it using the standard java mail classes? If you dont want to use Sun's JCE, you can have a look at www.cryptix.com ciao miki