Someone sending spam from my account

Hello,

Someone emailed me today and forwarded me some spam that supposedly came from my address, which he is reporting to the state attorney general. Is there any way I can prevent people from using my address to send spam?

Thanks in advance,
Midori

dont leave your email everywhere, and when you do just write something like myemail@yahoo.NOSPAMHERE.com
obviously, people will delete NOSPAMHERE when sending email to you.
P.S. reporting to the state attorney general ... yeah like they care

Thanks, Al! Unfortunately, my address is posted all over our company web site, so you confirmed my suspicions that there's nothing I can do.

Take care!
-Midori

>> Is there any way I can prevent people from using my address to send spam?

No.

>> which he is reporting to the state attorney general

You shouldn't be worrying at all. If he really is going to report that to state attorney, I bet they will send his email to /dev/null.
First, you need to know what envelope sender is. That is, one can specify any envelope sender (the from email). So that person obviously is technical illiterate and doesn't have a clue how SMTP works.