SPF (Sender Policy Framework)

What Is SPF?

SPF (Sender Policy Framework) is an email authentication protocol that helps mail servers verify whether a message was sent from an authorized source.

It works by checking the sending mail server’s IP address against a list of approved servers published in the sender’s DNS record. If the IP address is not on the list, the message may be flagged as suspicious or rejected.

SPF is one of the three core components of modern email authentication, alongside DKIM and DMARC.

How Does SPF Work?

Every domain that sends email can publish an SPF record in its DNS configuration. This record, stored as a TXT entry, lists which servers or IP addresses are allowed to send messages on behalf of that domain.

A typical SPF record looks like this:

When a recipient’s mail server receives an email, it performs an SPF check:

1. It extracts the envelope-from domain from the message header.
2. It looks up that domain’s SPF record.
3. It checks whether the sender’s IP address matches an authorized entry.
4. Based on the result (pass, fail, softfail, or neutral), the mail server decides how to treat the message.

SPF focuses on verifying the sender’s mail infrastructure, not the content of the message itself.

Strengthening Email Authentication with SPF

SPF provides an important layer of defense against spoofing and phishing, but it is most effective when combined with DKIM and DMARC.

Because SPF only validates the sending IP, attackers can still forge the visible “From” address. That’s where DMARC adds value by enforcing alignment between the SPF-authenticated domain and the domain that users actually see.

To maintain reliability, organizations should:

• Keep SPF records simple and within the DNS lookup limit (10).
• Regularly update records when new sending services are added.
• Monitor SPF performance and results through DMARC reporting tools.

SPF and DMARCeye

DMARCeye helps organizations monitor how SPF authentication performs across all sending sources.

By analyzing DMARC aggregate reports, DMARCeye identifies which servers pass or fail SPF checks and whether those results align with your DMARC policy.

This insight helps teams detect unauthorized senders, fix misconfigurations, and maintain strong domain reputation while progressing toward full DMARC enforcement.