Understanding Gmail and Yahoo DMARC Requirements
Concluding the Experiment: SPF Flattening
SPF Best Practices: Avoiding SPF Record Flattening
SPF-Identified Servers—What is this Source?
Why SPF Is So Funky in Today’s Modern World
SPF Pitfalls: Clutter Clouds Your Security Footprint
SPF Problems with MailChimp
What is the difference between SPF ~all and -all?
SPF Management Challenges