From your Yahoo mail account, you need to enable POP Access and Forwarding. Select Options in the left gutter, then POP Access & Forwarding under Mail Management. You need to have Web and POP Access enabled. You then MUST use your Yahoo address as the FROM address when sending the message. The basic mail sending program already included in the FAQ works with one minor change: you must POP authenticate yourself first before sending the message:

Store store = session.getStore("pop3");
store.connect("pop.mail.yahoo.com", username, password);

The authentication seems to last for about 30 minutes or so, so you don't have to authenticate yourself each time you send a message with JavaMail if you know you've authenticated yourself within the last half hour.

Hi,

I don't think you can send an email using their SMTP. I think only mail sent using the yahoo web mail is allowed to use it. It's a normal precaution for avoiding spam.