I am concerned that someone knew my email password and was reading my messages. (I've changed the password) Does Yahoo log all login sessions for an account, and possibly the IP address for the person that logged in? Yahoo, Hotmail etc I would think require a court order to give such information.
Is there another way to trace who logged into my Yahoo account?
BTW, when you change a password for an account you should also change the security questions and answers. It's OK to make up fake answers for the questions that people you know (or don't) can't research the correct answers. Here are some additional tips for creating new passwords :