From Lunarpages Web Hosting Wiki
What is JavaMail?
JavaMail is a collection of .jar files that can be used to provide mail functionality to Java applications and servlets.
To use JavaMail with your web application or scripts, you must upload the activation.jar and mail.jar into your WEB-INF/lib directory. The "mail.jar" file can be obtained from JavaMail API archive available for download at http://java.sun.com/products/javamail/downloads/index.html. The "activation.jar" is a part of the Java Activation Framework that can be downloaded from http://java.sun.com/products/javabeans/jaf/downloads/index.html
Set the SMTP host to "localhost" so you won't need to authenticate. Please also read the readme file included with the war on what settings need to be changed.