Review your Relaylist
Do you trust all IPs in the Relaylist?
Make Sure Antispam is enabled outbound
Navigate to GUI > Mail Policies > Outbound Mail Policies
Look for Default Policy
Click on Ironport Anti-Spam under the antispam column
Under Anti-Spam Settings click "Use IronPort Anti-Spam Service"
Specify an action like Spam Quarantine or Drop.
Submit and Commit changes
Proactive Measures
Finding a Spammer is all about finding the source IP address.
Please review the suggestions outlined in the article below for some pro-active steps and let me know if you have any questions.
