/ˈɛs-pi-ɛf/
n. “Verify the sender before you open the mail.”
SPF, short for Sender Policy Framework, is an email authentication method designed to detect and prevent email spoofing by verifying that incoming mail from a domain comes from an authorized IP address. It allows domain owners to publish a list of IP addresses or servers permitted to send email on their behalf in their DNS records.
When an email arrives, the receiving server checks the SPF record of the sender's domain. If the sending IP matches an authorized entry, the email passes the SPF check. If it does not match, the server can mark the message as suspicious, flag it as spam, or reject it entirely. This simple verification step helps reduce phishing, spam, and forgery.
For example, if example.com authorizes only its mail server at 192.0.2.1 to send messages, any email claiming to be from example.com but sent from another server will fail SPF validation. This protects recipients from fake emails that attempt to impersonate the domain.
SPF works best in combination with DKIM and DMARC. While SPF ensures the sending server is authorized, DKIM verifies message integrity, and DMARC provides enforcement and reporting. Together, these three form a layered defense against email-based attacks.
Implementing SPF involves creating a TXT record in the DNS zone of the domain. The record lists IP addresses, hostnames, or mechanisms that define authorized senders. Regular review and updates are essential to account for new servers, third-party email services, or cloud providers used to send email on behalf of the domain.
Beyond security, SPF also improves email deliverability. Legitimate messages that pass SPF checks are less likely to be flagged as spam, helping maintain trust with recipients and email providers. Misconfigured SPF records, however, can lead to legitimate mail being rejected, so careful setup is critical.
In summary, SPF is a frontline mechanism to verify senders, reduce impersonation, and improve email trust. It’s straightforward to implement, widely supported, and a key part of modern email authentication alongside DKIM and DMARC.