When you sign up for a Google Apps acount, you agree not to use the account to send spam, distribute viruses, or otherwise abuse the service. All users on your domain are subject to these agreements, which are part of the Google Apps Acceptable Use Policy.
If Google identifies a Google Apps user who is violating these agreements, we reserve the right to immediately suspend the user. If the problem is domain-wide, we reserve the right to suspend the entire account and deny administrator access to all the Google Apps services. In such cases, we send a notification to the registered secondary email address for the domain administrator.
If you identify a Google Apps user who is violating these agreements, at your domain or another domain, you can report the abuse to Google by sending an email message to email@example.com or firstname.lastname@example.org, where domain.com is the domain where the abuse occurs. Google monitors these addresses for every domain registered with Google Apps.
Since abuse and postmaster are reserved aliases, you cannot to use them as user names or aliases. You can, however, subscribe to them and receive all mail sent to these addresses. (Learn more)