Every so often I receive junk mail from my own email address? How do they do this?

I know all about Phishing, so I don't think that's what is happening. And I've changed my password just to be safe. Has anyone had this problem?
Every so often I receive junk mail from my own email address? How do they do this?
E-mail messages are really just specially formatted text messages, but your e-mail program hides the formatting from you. The Sender e-mail address is nothing more than a line in what's called the header of the message that says who it's from. This is no guarantee it's actually from the person with that e-mail address.
Reply:i don't know how they do this but i'm guessing that it's yahoo selling a product or trying to sell you a product they're endorsing. you can always block you're own address.