What is SPF? Sender Policy Framework (SPF) explained

Sendmarc makes managing SPF easy, with tools to create, deploy, monitor, and optimize SPF records, helping your domain stay secure and compliant without the technical hassle. 

Many businesses start by asking “What is SPF in email?” and why it matters for email security. The answer is simple: SPF protects your domain from spoofing and unauthorized senders. 

For anyone still wondering ”What is SPF?” it’s the backbone of domain-level email protection that ensures only trusted servers can send on your behalf. 

What Is Spf

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What is SPF: What is an SPF record?

What is SPF in email? Sender Policy Framework (SPF) is an email authentication method created to prevent email spoofing. It does this by allowing domain owners to specify which email servers are authorized to send email on behalf of their domain. This is achieved by publishing a special TXT record – known as an SPF record – in the DNS. Understanding “What is SPF in email” often comes down to looking at real record examples. 

A record will typically have the following structure:

HostTypeValue
@TXTv=spf1 [mechanisms] [qualifiers]

Here is an example of what a record might look like:

HostTypeValue
@TXTv=spf1 mx include:spf.protection.outlook.com ~all

Grasping “What is SPF in email means understanding that every mechanism and qualifier inside the TXT record plays a role in protecting your domain.

Mechanisms in SPF records

To fully answer the question “What is SPF in email?”, you also need to know about the mechanisms that define authorized servers.  

SPF records use a set of mechanisms to define which email servers are authorized to send email on behalf of a domain. These mechanisms decide how the receiving email server validates the sender’s IP address.

The most commonly used mechanisms include:

  • ip4 & ip6: Specifies authorized IPv4 and IPv6 addresses.
  • a: Authorizes any IP address associated with the domain’s A or AAAA DNS records.
  • mx: Authorizes IP addresses of the domain’s Mail Exchange (MX) servers.
  • include: References the SPF record of another domain. This is commonly used when third-party providers are authorized to send emails on behalf of the domain.

Qualifiers in SPF records

Another important part of understanding “What is SPF in email involves qualifiersQualifiers determine how the receiving server should handle emails that don’t match the specified mechanisms:

  • +all: Pass (the email is accepted even if it doesn’t match any mechanism)
  • -all: Fail (the email is rejected if it doesn’t match any mechanism)
  • ~all: Softfail (the email is accepted but marked as suspicious if it doesn’t match any mechanism)
  • ?all: Neutral (the email isn’t accepted or rejected – this qualifier treats the message as if there’s no SPF policy)

Modifiers in SPF records

Modifiers in SPF records provide extra functionality. They help enhance the flexibility and clarity of SPF policies.

The two commonly used modifiers are:

  1. redirect: Redirects the SPF check to another domain’s policy. This is useful when a domain’s email policy is fully managed by another domain.
  2. exp: Defines a custom message that can be shown when an SPF check fails, helping explain why the email was rejected.

What is SPF: Process

When explaining “What is SPF in email,” its usually broken into four stages: 

  1. SPF record creation: The domain owner creates an SPF record that lists all servers authorized to send email on behalf of the domain. This record is then published in the domain’s DNS.
  2. Email sending: When an email is sent, the receiving server performs a DNS lookup to find the domain’s SPF record.
  3. SPF check: The receiving server compares the sender’s IP address against the authorized sources listed in the SPF record.
  4. Action based on qualifier: Based on the result of the SPF check and the qualifier in the record, the receiving server will accept, reject, or flag the email as suspicious.

This step-by-step flow shows “What is SPF” in action, turning policy settings into real-time protection against spoofing. 

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What is SPF: Integrations

Those researching “What is SPF in email” often realize it works best when combined with DomainKeys Identified Mail (DKIM) and Domain-based Message Authentication, Reporting, and Conformance (DMARC) 

SPF works alongside these email authentication protocols to provide a more comprehensive approach to email security. When implemented together, these protocols help protect domains from spoofing, phishing, and other types of email-based attacks.  

  • DKIM: DKIM adds a digital signature to each outgoing email, allowing the receiving server to verify that the message wasn’t altered.
  • DMARC: DMARC builds on both SPF and DKIM by allowing domain owners to define a policy for how receiving servers should handle emails that fail authentication checks.

By learning “What is SPF in email” and how it integrates with DKIM and DMARC, you gain a full picture of modern email authentication.

Ready to safeguard your domain? Contact us today to get started! 

What is SPF: FAQs

What is SPF in email?

What is SPF in email? Sender Policy Framework (SPF) is an email authentication protocol that enables domain owners to specify which IP addresses are authorized to send emails on behalf of their domain. This helps prevent email spoofing and improves the trustworthiness of outgoing messages.

SPF works by using a DNS TXT record to list the servers that are allowed to send emails from a domain. When an email is received, the recipient’s email server performs a DNS lookup and checks the sender’s IP address against the SPF record to verify whether the email is legitimate.

When organizations ask, “What is SPF best for? the answer is preventing spoofing, phishing, and improving deliverability. It also helps ISPs and email platforms validate incoming emails and filter out unauthorized messages.

The limitations of SPF include its inability to handle email forwarding, which can cause legitimate emails to fail SPF checks. SPF records must be updated regularly to remain accurate, which can be time-consuming. SPF is also subject to a 10 DNS lookup limit, which may require SPF flattening to manage complex records.

No, you can’t have multiple SPF records for a single domain. Instead, all authorized IP addresses and mechanisms must be included within one SPF record. Having multiple records will cause SPF validation to fail.

SPF integrates with DomainKeys Identified Mail (DKIM) and Domain-based Message Authentication, Reporting, and Conformance (DMARC) to provide layered email authentication. DKIM uses cryptographic signatures to confirm email content integrity, while DMARC combines the results of SPF and DKIM checks and allows domain owners to set policies for handling authentication failures.

It is important to keep SPF records updated to ensure that all authorized email-sending servers are correctly listed. One of the key lessons from learning “What is SPF” is that records must stay updated; otherwise, legitimate messages risk being rejected.   

In summary, understanding “What is SPF” is essential for anyone who wants to secure their email domain and build trust with recipients.