I regularly have emails in my Junk folder that when i try to block the email address of the sender, the sender address is mine.
dave
If anyone in your address book gets junk mail like that from your email addy, change your password. Its not as big a problem with ISP based email servers as the more common web based ones, but there are bots that can hack email accounts and send emails out to everyone in your addy book. A password change will stop it. A strong password will end it.