Here are some links to sites with lots of good information on Internet mail and some articles on the Jakarta Mail API. If you know of other good sources of such information, please let us know at mail-dev@eclipse.org.
JavaMail Client on the NetBeans Platform by Geertjan Wielenga (first of a multi-part series)
Test email components in your software by Jason Kitchen
JavaMail Quick Start by Tony Loton
Java Tip 115: Secure JavaMail with JSSE by Eugen Kuleshov and Dmitry I. Platonoff
How Internet Mail Works by Dave Sill
SMTP Inside Out by Heinz Tschabitscher
E-mail in Wikipedia
How E-mail Works by Marshall Brain and Tim Crosby
Deciphering Internet E-mail in Webopedia
JavaMail, by Ian Moraes, in Java Developer’s Journal, October 1999 (Registration required.)
What Is JavaMail?, by Rachel Gollub, in Java Developer’s Journal, October 1999 (Registration required.)
Managing e-zines with JavaMail and XSLT, Part 1 by Benoît Marchal
Managing e-zines with JavaMail and XSLT, Part 2 by Benoît Marchal
Introduction to the Java Mail API by Tony Nemil and Anil Hemrajani