The SPFBL service is a combination of the concepts of SPF and DNSBL. The purpose of this service is to improve SPF processing and reduce the amount of external queries from an e-mail server, which uses SPF and at least some DNSBL service.
Once the service is started, queries can be made by client programs, such as the “spfbl.sh” script. Attention! The “spfbl.sh” script requires the “netcat” (command “nc”) package installed to work correctly.
The listing is made through the SPFBL ticket, which is sent together with the query’s SPF qualifier: