Anti-Spoof Settings
Go to Filter Rules > Anti-Spoofing Settings to access SpamTitan anti-spoof functionality. The Anti-Spoof Domains window shows a list of your domains:
Check the box 
to the left of the domain you want to edit and click the edit 
icon or Edit button. Check multiple boxes to edit multiple domains at once.
The Anti-Spoof Settings window displays for your selected domain(s):
Follow the steps below to enable and modify your anti-spoof settings.
By default, anti-spoof settings are not enabled. Click Enable and the display expands:
Use SPF Record for IP Validation: Enable this option to use your SPF record to determine if a sender is valid instead of specifying IPs in the IP List. By default, this option is not enabled.
IP List: If you have not enabled Use SPF Record for IP Validation, you can add a list of CIDR notation ranges here that are allowed to send email using your domain. Click Add... to add an entry. Once added, click the edit
icon to edit an IP, or the delete 
icon to delete an IP from the list.Using IP List is more secure than using Hostname List. Generally, try to use Hostname List only if you are not using SPF and a service you are using has too many IPs to list.
Hostname List: Click Add... to enter hostnames that are allowed to send email using your domain, e.g. www.example.com.
Enter example.com to include any sub-domains such as support.example.com, mail.example.com, docs.example.com, etc.
Regular expression patterns can be used here, but are not necessary. If using regular expression, note that the more generic the expression, the easier it is to bypass spoofing.
Click Save to save changes to all domains and return to the Anti-Spoof Domains window.
Warning
If you do not click Save when editing multiple domains, only changes to the first domain checked will be saved.