There is an Android-friendly port of javamail which you should be using. There are three libraries that you need to include in your app: mail.jar, activation.jar, and additionnal.jar(sic). It looks like you are missing something that the activation library depends on, and this could be because you are not using the Android port of this library.
I have used the Android-friendly version of javamail successfully in a project, and it works really well.