Definition
Sender Policy Framework (SPF) is an email authentication standard published as a DNS TXT record at the sender's domain. The record lists IP ranges and include directives authorized to send mail for the domain. Receivers query the SPF record on inbound mail and verify the sending IP against it; failures contribute to spam scoring and DMARC alignment. SPF has a hard 10-DNS-lookup limit; complex sender ecosystems often hit it and require SPF flattening (replacing include directives with literal IP ranges). SPF is one of the three legs of email authentication (SPF, DKIM, DMARC) and is necessary but not sufficient - forwarding breaks SPF alignment, which is why DKIM matters too.
Related terms
- DMARC (Domain-based Message Authentication, Reporting and Conformance) - Email authentication standard that lets domain owners specify how receivers should treat mail that fails SPF or DKIM.
- DKIM (DomainKeys Identified Mail) - Email authentication using cryptographic signatures placed in headers by the sending mail server.
- BEC (Business Email Compromise) - Email fraud where attackers impersonate executives or trusted partners to authorize fraudulent wire transfers or data disclosure.