SPF (Sender Policy Framework)

SPF is a DNS-based authentication mechanism that helps prevent email spoofing by allowing domain owners to publish a list of authorized sending IP addresses and mail servers.

Why it matters

• Prevents spammers and attackers from sending emails that appear to come from your domain.
• First line of defense against email spoofing and domain impersonation.
• Required by most email providers for optimal deliverability.
• Works together with DKIM and DMARC for comprehensive email security.
• Protects your domain reputation and prevents blacklisting.

How it works

• Published as a TXT record in your domain's DNS: v=spf1 include:_spf.google.com ~all
• Receiving servers check if the sending IP is listed in your SPF record.
• SPF result (pass, fail, softfail, neutral) is used by DMARC for policy enforcement.
• Supports mechanisms: ip4, ip6, a, mx, include, and all.
• Allows up to 10 DNS lookups to prevent abuse and performance issues.

How to implement

• Identify all legitimate email sources (mail servers, marketing platforms, CRM systems).
• Create SPF record starting with v=spf1 and listing authorized sources.
• Use "include:" for third-party services (Google Workspace, Microsoft 365, SendGrid).
• End with ~all (softfail) for testing or -all (fail) for strict enforcement.
• Monitor for SPF lookup limit (10 maximum) and use SPF flattening if needed.
• Test with email authentication tools before deploying.