If you see that spam has been sent from your own email address, there is no need to panic. The email is not really sent from your own account. It is sent from another, but the email's header has been changed to your email address or another from your domain. This is a common spammer technique called email spoofing or domain spoofing. This is done in order to bypass the server's and your email software's spam filters. We use a counter technique called SPF, which basically prevents spammers from using your email address or your domain to spoof other recipients. Though it is not a perfect solution, it does work pretty well. If you continue to receive spam of this kind, please try creating your own spam filter as per this article.