One of my users received a spam message from his internal exchange server on an SBS 2003 machine. The message apparently orginated from an unknown user from his own domain. (i.e. Chris@abc.com received a spam message from John@abc.com) However, john@abc.com does not exist and there is no mailbox for him. I checked and there are no open relays. What do I need to do to figure out how this happened and how to stop it? The message did show up in the message tracking center. With the following info:
9546270937.20111128072226@abc.com
SMTP:Message Submitted to Advanced Queuing
SMTP:Started Message Submission to Advanced Queue
SMTP:Message submitted to Categorizer
SMTP:Message Categorized and Queued for Routing
SMTP:Message Queued for Local Delivery
SMTP:Message delivered locally to chris@abc.com
SMTP:Store Driver: Message Delivered Locally to Store to chris@abc.com