为什么此Java Mail调用在JDK 1.5中失败，但在1.6中成功？

Question

When I run the following code with JDK 1.5, the last line fails, but when I run it with JDK 1.6 it succeeds. Why is this?

Code:

Session session;
session = Session.getDefaultInstance(properties,
new javax.mail.Authenticator() {
    protected PasswordAuthentication getPasswordAuthentication() {
            return new PasswordAuthentication(username, password);
    }
});

// Create a default MimeMessage object.
MimeMessage message = new MimeMessage(session);

Answer 1

通过询问有关缺少激活JAR的评论来得出结论。