Enabling HELO DNS lookup
Whenever a client opens an SMTP session with a server, the client sends a HELO command with the client domain name. When you enable HELO DNS lookup, your FortiGate unit will take the domain the client submits as part of the HELO greeting and send it to the configured DNS. If the domain does not exist, your FortiGate unit will treat all messages the client delivers as spam.
The HELO DNS lookup is available only for SMTP traffic.
To enable HELO DNS lookup
1. Go to Security Profiles > Email Filter > Profile.
2. The default email filter profile is presented. To edit another profile, select it from the drop down in the Edit Email Filter Profile title bar.
3. Select Enable Spam Detection and Filtering and select Apply
4. Under the heading Local Spam Filtering, select HELO DNS Lookup.
5. Select Apply.
Select the edited email filter profile in a security policy, and the traffic controlled by the security policy will be scanned according to the settings you configured. You may select the email filter profile in more than one security policy if required.