Kerio Mail Server Spam Filtering
Kerio Mail Server has several configuration options to protect against spam email. For maximum protection, you should investigate and set all appropriate items.
Under the Security Options tab for the SMTP server are several limits and controls you can set.
*Maximum number of messages per hour from one IP address.
* Maximum number of concurrent SMTP connections from one IP address.
*Block if sender's mail domain was not found in DNS.