What is a Sender Policy Framework?

A Sender Policy Framework (SPF) is an email authentication method. It helps to fight email spoofing and ensure that emails are sent from authorized mail servers. It works by verifying sender IP addresses against a published list of authorized sending hosts and IP addresses for a domain. In doing so, SPF helps maintain the integrity and trustworthiness of email communications.



Development of Sender Policy Framework

The Sender Policy Framework was developed to respond to the increasing problems of email spoofing. This is a cyber attack whereby the attackers impersonate a legitimate email sender to send phishing emails or spread malware.


The Sender Policy Framework protocol was first introduced in 2003 and has since become a standard practice for email authentication, as described in RFC 7280. Its implementation is part of a broader suite of technologies, including DKIM and DMARC, which collectively upgraded email security.



The Core Functionality of SPF

The primary job of SPF is to authenticate email senders by verifying if incoming mail from a domain comes from a host authorized by that domain’s administrators. It achieves this through several key components:


  1. Sender policy framework record:

    An SPF record is a TXT record in the domain’s DNS settings that lists the servers allowed to send emails on behalf of the domain. This record specifies IP addresses or a range of IP addresses and may include mechanisms and modifiers to refine the policy.

  2. Email Verification:

    When an email is sent, the receiving server retrieves the SPF record from the sender’s domain DNS. It then checks if the IP address of the mail server sending the email is listed in the SPF record.

  3. Policy enforcement:

    The SPF protocol specifies how receiving servers should handle emails that fail Sender Policy Framework checks. Actions can range from accepting the email but marking it to rejecting it outright, depending on the domain’s specified policy.



How does SPF work?

Implementing a Sender Policy Framework for your email domain involves several straightforward steps:

  • Sender policy framework record creation:

    The domain added an SPF record in their DNS records. This record outlines which mail servers are permitted to send emails from the domain.

  • Email sending:

    When an email is sent from the domain, it passes through the designated email domain server (MX Records).

  • SPF verification by the receiver:

    The receiving mail server checks the SPF record of the sender’s email domain DNS to verify that the email comes from an authorized server.

  • Action based on SPF result:

    Depending on the results of the SPF check, the receiver can accept, reject, or flag the email as spam.



SPF’s Role in Email Security in 2024

Sender Policy Framework is important in preventing email spoofing and phishing, key components of many cyber attacks. By providing a method to authenticate sender identity, SPF helps to:

  • Reduce spam and phishing:

    By verifying sender identities, the Sender Policy Framework makes it harder for attackers to spoof emails, thereby reducing the effectiveness of spam and phishing attacks.

  • Improve email deliverability:

    Legitimate emails are less likely to be mistaken for spam if they pass Sender Policy Framework checks, improving deliverability.

  • Increase trust in email:

    Organizations that implement SPF contribute to a broader trust in their email communications, reassuring recipients about the authenticity of their messages.

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