摘录自：http://stackoverflow.com/questions/1630002/java-lang-noclassdeffounderror-javax-mail-authenticator-whats-wrong

You need to add two jars into the WEB-INF/lib directory or your webapp (or lib directory of the server):

• mail.jar - contains the actual smtp implmentation
• activation.jar - needed by mail.jar

java.lang.NoClassDefFoundError: javax/mail/Authenticator