How can I send mail when I don't have the JavaMail libraries installed?
Assuming you have access to an SMTP server that will accept your request, you can either open up a socket connection to port 25 and send the raw SMTP commands, or use the non-standard sun.net.smtp.SmtpClient class that is provided with Sun's development environments.
Keep in mind that both the JavaMail library and JavaBeans Activation Framework are in javax.* packages and thus downloadable to an applet.
In the case of an untrusted applet, the web server and SMTP server must be the same machine.