man qmail-smtpd modified excerpt:
You can add a single line with SPF rules (also known as SPF mechanisms) that will be checked before other SPF rules would fail. This can be used to always allow certain machines to send certain emails.
As an example, an spfrules file that contains the line ip4:192.0.0.1/24 would allow the local qmail-toaster to receive Email from one of its supported domains from any host with the ip addresses 192.0.0.1 through 220.127.116.11.
A more complete description of the SPF mechanism syntax can be found here .