PS This, from the Javamail FAQ, may also help...
Q: I'm having trouble logging into my Microsoft Exchange server, even though I'm sure I'm using the correct username and password, what could I be doing wrong?
A: When logging in to Exchange you need to use a username that's more than your simple login name. For example, if your email address is "J.User@server.com", your Windows NT login name is "juser", your NT domain name is "dom", and your Exchange mailbox name is "Joe User", then you would need to use a username of "dom\juser\J.User" when logging in using JavaMail.
Howard
http://www.avoka.com