SPF
Sender Policy Framework
An email authentication method that specifies which servers can send email for a domain.
Definition
Sender Policy Framework (SPF) is an email authentication standard that allows domain owners to specify which mail servers are authorized to send email on behalf of their domain. Receiving mail servers check SPF records (published as DNS TXT records) to verify that incoming mail claiming to be from a domain comes from an authorized server, helping prevent email spoofing.
Examples
SPF Record Example
A typical SPF DNS record with common mechanisms.
; SPF DNS Record (TXT)
example.com. IN TXT "v=spf1 ip4:192.0.2.0/24 include:_spf.google.com include:sendgrid.net -all"
; Mechanisms:
; v=spf1 - SPF version
; ip4: - Authorized IPv4 addresses
; include: - Include another domain's SPF
; a - Domain's A records are authorized
; mx - Domain's MX records are authorized
; -all - Reject all others (hard fail)
; ~all - Soft fail (accept but mark)
; ?all - Neutral (no policy)Use Cases
Best Practices
- List all legitimate sending sources
- Use include: for third-party services
- End with -all for strict enforcement
- Keep SPF records under 10 DNS lookups
- Monitor for SPF failures in DMARC reports
FAQ
Related Terms
DMARC
An email authentication protocol that protects against phishing and spoofing.
SPF is part of DMARC authentication
DKIM
An email authentication method that uses cryptographic signatures to verify message integrity.
Complementary email authentication
DNS
Domain Name System - translates human-readable domain names to IP addresses.
SPF records are DNS TXT records
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