Firewall configuration / TEST TOOL
To prevent spam and viruses from bypassing the Spam-Filter, it's recommended (but not mandatory) to lock down the firewall of your mailserver. This means limiting SMTP (PORT:25) traffic at the firewall level to only allow connections from Spam-Filter.com IP addresses.
Spam-Filter.com utilizes three (3) data centers:
After making the restrictions to port:25, you can use this tool to test your configuration. If successful, you should receive three (3) emails, one from each data center.