Java APIs

I have installed mail.jar and activation.jar in JAVA_HOME/jre/lib/ext which should automatically be on the classpath.

I have a file TransportSendExample.java that imports classes from these jar files.

If I run: javac TransportSendExample.java
It works no problem.

I then try: java TransportSendExample
And I get: Exception in thread "main" java.lang.NoClassDefFoundError: javax.mail.Address

So I try this to see if javap works:
javap javax.mail.Address
And I get everything I would expect:

public abstract class javax.mail.Address extends java.lang.Object
{
//all the methods
}
i.e. javap locates the class.

So what is happening. I cannot see how this could be a classpath problem since javap locates the class.

Any advice would be greatly appreciated.

Tim.