Legal Question in Technology Law in California

Not enough facts given. If by "my" computer you mean one assigned to you at work, it is not illegal for the boss to look at what's on the machine. If you are under 18, your parents can read your e-mail quite legally. Beyond that, it probably depends upon whether you had a reasonable expectation of privacy. If you left the computer on with an e-mail on-screen, probably not illegal for someone to read it. Beyond that, possibly to probably an illegal invasion of privacy. I suggest you use a password to limit access to your computer.