The Postwhite script can be used to generate whitelists and/or blacklists of IP addresses and CIDR subnets based on the SPF records of selected domains. These whitelists/blacklists can then be used by the Postscreen Postfix service to automatically allow or deny connections to specific SMTP clients. This is useful for accepting messages from big mail providers like Google and Outlook which may resend mail messages from different IP addresses, which in turn interferes with Postscreen SMTP client greylisting.

The debops.postwhite Ansible role will install Postwhite script and configure Postfix automatically using the debops.postfix Ansible role, as long as the Postscreen configuration is enabled by the debops.postscreen role. See the documentation of the mentioned roles for more details.