What is SPF?

What is SPF?

SPF (Sender Policy Framework) is an email authentication standard that helps protect domains from unauthorised email use.

It allows a domain owner to specify which mail servers and services are authorised to send email on behalf of their domain.

When an email is received, the recipient's email system can check the domain's SPF policy to determine whether the sending server is authorised. This helps identify potentially fraudulent messages and reduces the risk of email impersonation.

Why is SPF Important?

Email remains one of the most common attack methods used by cybercriminals. Without proper controls, it is relatively easy for attackers to send messages that appear to come from a legitimate organisation.

These messages may be used to:

• Impersonate trusted businesses
• Steal usernames and passwords
• Deliver malware
• Conduct invoice fraud
• Damage a company's reputation

SPF helps reduce these risks by providing a way for organisations to declare which systems are permitted to send email using their domain.

How SPF Works

Every organisation uses one or more systems to send email.

These may include:

• Microsoft 365
• Google Workspace
• Marketing platforms
• CRM systems
• Helpdesk solutions
• Accounting software
• Website contact forms
• Third-party suppliers

SPF acts as an authorised sender list. When a message is received, the recipient can compare the sending server against the domain's published SPF policy to determine whether the sender is recognised.

If the sender is not authorised, the message may be flagged as suspicious or handled according to the recipient's security policies.

SPF Helps Build Trust

A correctly configured SPF policy helps receiving email systems distinguish between legitimate email and potentially fraudulent messages.

Benefits include:

• Reduced risk of domain spoofing
• Improved email deliverability
• Better reputation with receiving email providers
• Increased confidence in legitimate email communications
• Stronger overall email security posture

SPF is one of the foundational technologies used to secure business email.

SPF Can Become Complex

Many organisations start with a simple email environment but gradually add more systems that send email on their behalf.

Over time, domains may send email from:

• Multiple cloud platforms
• Marketing services
• Automated applications
• Business software integrations
• External suppliers

As these systems are added, removed, or changed, SPF policies often become increasingly complex.

An incomplete or inaccurate SPF configuration can lead to:

• Legitimate emails being rejected
• Important messages being delivered to spam folders
• Security gaps that attackers may exploit
• Difficulty identifying authorised senders

SPF is Only Part of the Picture

While SPF is an important security control, it is not designed to work alone.

Modern email security relies on multiple technologies working together, including SPF, DKIM, and DMARC.

Each technology plays a different role in verifying the authenticity of email and protecting organisations from impersonation attacks.

Why Ongoing Monitoring Matters

Email environments change constantly. New services are introduced, suppliers change, and applications are retired.

As a result, SPF policies should not be treated as a one-time configuration task.

Regular monitoring helps organisations:

• Identify unauthorised sending sources
• Detect configuration issues
• Maintain email deliverability
• Reduce security risks
• Ensure email authentication remains effective

Without visibility into how a domain is being used, problems can remain hidden until legitimate email starts failing or a security incident occurs.

Why Organisations Implement SPF

Organisations typically use SPF to:

• Protect their domains from unauthorised use
• Improve email deliverability
• Reduce spoofing and phishing risks
• Support cyber security best practices
• Build trust in their email communications
• Form part of a broader email authentication strategy

SPF is a key component of modern email security and remains one of the most widely adopted email authentication standards.