JavaMail builds fine with Maven 2.2.1, but it needed to be updated to build with Maven 3, included with NetBeans.
If you want to build the source you have, tell NetBeans to use an external version of Maven, and use 2.2.1.
I've pushed out the updated version to the source repository, so if you update to the latest source it should
be buildable in NetBeans.
Let me know if you have any other problems with the build.