How to stop people from using my domain to send spam?

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http://serverfault.com – I receive Mailer Daemon messages saying certain emails fail. My domain is itaccess.org which is administered by google apps. Is there any way I can identify who is sending emails from my domain, and how they are doing it without me creating an account for them? Delivered-To: [email protected] Received: by with SMTP id z34csp12042wfd; Wed, 8 Aug 2012 07:12:46 -0700 (PDT) Received: by with SMTP id in2mr18229790lab.6.1344435165782; Wed, 08 Aug 2012 07:12:45 -0700 (PDT) Return-Path: <[email protected]> Received: from smtp-gw.fsdata.se (smtp- (HowTos)