Urgh.  I just spent a few hours trying to figure out why JNDI JavaMail session stopped working.  Previously, I had Tomcat 5.0.26 beta installed and it was working just fine.  In an attempt to debug another problem, I peddled back to 5.0.25, which is the latest version without any beta tag, and found that I couldn't send e-mail out from an webapp.  Error message was rather bland so it took me a while to find the relevant bug report.  Guess what?  5.0.25 build left out some key classes related to JNDI JavaMail session support.  Heck, I think I'll go back to the beta version and keep my fingers crossed.