What is SPF For Email?

SPF stands for Sender Policy Framework. It is an email authentication protocol designed to detect email spoofing and prevent unauthorized senders from sending messages on behalf of a particular domain. Every 39 seconds, a cyberattack occurs across the globe, most of which may be perpetrated through email. SPF helps authorize your senders so that your domain cannot be manhandled by an unauthorized third party email sender. SPF or Sender Policy Framework is an email authentication protocol that allows only specific IPs to send emails using a domain name. Any IP address outside the list will not reach the receiver’s mailbox as it leads to SPF failure. The SPF policy, defined in the DNS record, lists the mail servers authorized to send messages on behalf of your domain.

SPF email records help maintain a list of verified senders for your domain that can be publicly looked up and retrieved by receiving servers to authenticate emails and are mentioned under RFC 7208. It protects your email domains from hackers to steer clear of phishing, spamming, and email spoofing attacks. Email authentication techniques like SPF are ideal for keeping your email domain protected.

How does SPF work?

SPF works by allowing domain owners to publish a list of authorized email servers (IP addresses or hostnames) that are allowed to send emails on their behalf. Here is how SPF works step-by-step: 

1. Publishing your record for SPF

The domain owner publishes an SPF record in the DNS (Domain Name System) of their domain. DNS is a system that translates human-readable hostnames into machine-readable IP addresses. The SPF record is a DNS TXT record containing a list of servers authorized to send emails for that domain.

2. Your email is received

When an email is sent, it contains information about the sender’s domain, often found in the Return-Path address (also known as the envelope sender or MAIL FROM address), which specifies where bounced emails should go.

3. Extracting the Sender’s Domain

The recipient’s email server extracts the domain from the Return-Path email address in the email header.

4. DNS lookup is performed

The recipient’s email server performs a DNS lookup to retrieve the SPF TXT record of the sender’s domain identified in the previous step.

5. SPF authentication is performed

The SPF record contains a policy that defines which servers are allowed to send emails for the domain. The recipient’s email server compares the IP address of the server that sent the email against the list of authorized servers specified in the SPF record. The return path email address is cross-checked at the receiver’s end to verify whether or not the sending IP address is listed in the SPF records.

6. Final authentication result is determined

Based on the SPF check, the recipient’s email server determines whether the email came from an authorized server or not (Pass, Fail, SoftFail, Neutral, etc.).

7. Action is taken based on the results

The recipient’s email server takes action based on the SPF check result and the domain’s DMARC policy (if one exists). It could accept the email, mark it as spam, or reject it entirely. If the approval is positive, emails are typically sent to the inbox; otherwise, it may lead to SPF failure.

Set Up SPF with PowerDMARC!

How to use SPF With Your Email

To use the SPF email standard, you must make sure you have a proper understanding of how it works, and check your domain’s and email service provider’s SPF support. Following this, you can create a record for SPF, publish the record on your DNS, and ideally combine your SPF DNS implementation with DKIM and DMARC to prevent spoofing. It should be noted that SPF authenticates the sending server and does not necessarily validate the sender’s identity or message content. Using SPF with DKIM, DMARC, and potentially BIMI for more thorough email authentication can significantly improve your email security.

How to Enable SPF For Your Email

To create an SPF record, you need to follow these general steps:

Determine the authorized email servers

Identify the IP addresses or hostnames of all email servers that are authorized to send emails on behalf of your domain. This includes your own organization’s email servers, third-party email service providers (like Google Workspace, Microsoft 365, SendGrid, Mailchimp, etc.), and any other services that send email using your domain name. Collect a comprehensive list of all these IP addresses and sending domains.

Define your SPF policy

Determine the policy for SPF. This involves specifying which servers are allowed to send emails for your domain using SPF mechanisms. You also need to decide how strictly receiving servers should enforce the policy using qualifiers (e.g., `-all` for Fail, `~all` for SoftFail).

Determine SPF Format

SPF records are published as a TXT record in your domain’s DNS. The record should be in a specific format, starting with `v=spf1` followed by mechanisms, modifiers, and a final `all` mechanism with a qualifier.

Publish the SPF record

First, generate your SPF record. You can use our free SPF generator tool or manually construct the record based on your authorized senders and policy. Then, access your domain’s DNS management system, which is typically provided by your domain registrar or hosting provider. Locate the DNS settings for your domain and add a new TXT record. Specify the hostname (usually “@” or blank for the root domain itself) and paste the complete SPF record string into the value/data field.

SPF Record Example

An SPF record TXT in your DNS will look something like this:

This record defines a set of hosts as valid senders. For example, `v=spf1 ip4:192.168.0.0/16 include:spf.example.com -all` means:

• `v=spf1`: Specifies the SPF version being used.
• `ip4:192.168.0.0/16`: Authorizes emails sent from any IP address within this range.
• `include:spf.example.com`: Includes the SPF record from `spf.example.com`, effectively authorizing any senders listed there. This counts as one DNS lookup.
• `-all`: Indicates that any sender not matching the preceding mechanisms should fail the SPF check (be rejected).

The structure typically includes mechanisms, modifiers, and qualifiers:

Mechanisms:

These define the servers allowed to send email. Common mechanisms include: `a`, `mx`, `ip4`, `ip6`, `include`, `exists`, and `all`.

1. `ALL`: Matches always. Used for the end of the record (e.g., `-all`).
2. `A`: Matches if the sender’s IP matches the domain’s A or AAAA record.
3. `IP4`: Matches if the sender’s IP is within the specified IPv4 range.
4. `IP6`: Matches if the sender’s IP is within the specified IPv6 range.
5. `MX`: Matches if the sender’s IP matches one of the domain’s MX records’ IP addresses.
6. `PTR`: Matches if the PTR record for the sender’s IP points to a domain that resolves back to the sender’s IP. (Use discouraged due to inefficiency and unreliability).
7. `EXISTS`: Matches if the given domain name resolves.
8. `INCLUDE`: Includes the policy from another domain. Recursive processing occurs.

Modifiers:

These provide additional information or change how the record works. The main modifiers are `redirect` (points to another domain’s SPF record, replacing the current one) and `exp` (provides an explanation for SPF failures). Modifiers appear at the end, after mechanisms.

Qualifiers:

Prefixed to mechanisms to indicate how to treat a match:

• `+`: Pass (Default)
• `-`: Fail (Email should be rejected)
• `~`: SoftFail (Email should be accepted but marked/scrutinized)
• `?`: Neutral (No policy asserted; treat as None)

How to Check & Verify SPF?

Once you’ve set up your SPF record, it may take some time (up to 48 hours, though often much less) for the DNS changes to propagate across the internet. Use our SPF record check tool to validate and test your record. This helps verify the correctness of the syntax and ensures it is being recognized by DNS servers.

It’s important to note that SPF records can be complex, depending on the specific requirements of your email infrastructure. If you’re unsure about the syntax or need more advanced configurations, it’s recommended to consult your system administrator, IT support, or an email authentication expert for assistance in creating the SPF record correctly.

SPF for Third-Party Vendors

What is SPF for your third-party vendors? To authorize third parties (like marketing platforms, CRMs, helpdesks) to send email on your behalf, you need to include their specific IP addresses or their designated SPF-handling domains (using the `include:` mechanism) in your domain’s single SPF record. But beware, do not create multiple SPF records for the same domain, as this invalidates SPF entirely! All authorized senders must be listed in one consolidated record.

For example, if you use SuperEmails.net as your email sender, and their SPF-handling domain is spf.superemails.net, your SPF record might be:

v=spf1 include:spf.superemails.net -all

If you also use AnotherSender.com whose IPs are 1.2.3.4 and 5.6.7.8, you’d combine them:

v=spf1 ip4:1.2.3.4 ip4:5.6.7.8 include:spf.superemails.net -all

Why is Sender Policy Framework Important for Email?

SPF is important to ensure emails sent from your domain are genuine, and not fake lures created by cyberattackers to trick your customers, employees, or partners. With billions of spam emails sent daily, SPF is a foundational step in protecting your domain. Here are some key benefits of SPF: 

Reduced Email Spoofing and Averting Cyberattacks

SPF helps combat email spoofing by verifying the authenticity of the sending server. Malicious actors often use spoofed addresses for phishing, spamming, and other cyberattacks. A correctly configured SPF record makes it significantly harder for them to impersonate your domain successfully.

Improved Email Deliverability and Reduced Bounce Rate

Implementing SPF can enhance email deliverability rates. When recipient servers perform an SPF check and find that the sending server is authorized, they are more likely to accept the email rather than mark it as spam or reject it. Domains without proper SPF records may see higher bounce rates or have emails land in spam folders.

Reduced False Positives

By accurately identifying authorized email servers, SPF reduces the likelihood of legitimate emails being mistakenly marked as spam by receiving systems. This helps prevent false positives and ensures that important communications reach the intended recipients’ inboxes.

Enhanced Sender Reputation

SPF plays a role in building and maintaining a positive sender reputation with mailbox providers. By implementing SPF, domain owners demonstrate their commitment to email security and authentication best practices, which ISPs value.

Phishing and Spam Mitigation

SPF helps in reducing the effectiveness of phishing attempts and spam campaigns that rely on domain impersonation. SPF makes it more challenging for malicious actors to send fraudulent emails claiming to be from reputable domains.

Compliance with Email Standards and DMARC

Many email service providers and organizations encourage or require the use of SPF as part of their email policies. Furthermore, SPF is a foundational component of DMARC (Domain-based Message Authentication, Reporting, and Conformance). DMARC relies on SPF (and/or DKIM) alignment to determine how receiving servers should handle unauthenticated mail, making SPF essential for DMARC compliance.

What are the Limitations of SPF?

While SPF is a valuable tool, it has limitations:

• **Email Forwarding Issues:** SPF can encounter challenges with email forwarding. When an email is forwarded from one server to another, the original SPF authentication may fail because the forwarding server’s IP address is not listed in the SPF record of the original sender’s domain. DMARC helps mitigate this, but it remains a core SPF limitation.
• **Complexity and Management:** As the number of authorized email servers and third-party services increases, the complexity of managing and maintaining the single SPF record grows.
• **10 DNS Lookup Limit:** SPF records are limited to a maximum of 10 DNS lookups (mechanisms like `include`, `a`, `mx`, `ptr`, `exists`, and `redirect` count towards this limit). Exceeding this limit causes a permanent error (PermError), rendering the SPF record ineffective. Organizations using many third-party vendors often hit this limit. Tools like SPF flattening can help mitigate this by replacing lookups with static IP addresses, but require careful management.
• **255 Character String Limit:** A single TXT record string in DNS has a 255-character limit. While SPF records can span multiple strings within a single TXT record, overly complex records can become hard to manage and potentially exceed overall DNS record size limits. Exceeding the SPF string character limit within a single string will also invalidate the record.
• **Authenticates Sending Server, Not Content or ‘From’ Header:** SPF focuses solely on verifying the authenticity of the sending server based on the Return-Path domain. It does not provide encryption, verify the message content’s integrity (like DKIM does), nor does it directly authenticate the user-visible “From” address that recipients see. Attackers can sometimes bypass SPF by using an authorized server but spoofing the ‘From’ address.
• **No Reporting:** SPF itself does not provide visibility or feedback to the domain owner about authentication results or potential abuse. This is where DMARC becomes crucial, as it leverages SPF results and provides reporting.

Avoiding Common SPF Configuration Mistakes

Misconfigurations can render your SPF policy ineffective or even block legitimate email. Avoid these common pitfalls:

• **Using Multiple SPF Records:** A domain MUST have only one SPF TXT record. Multiple records will cause validation errors. Consolidate all authorized senders into a single record.
• **Incorrect Syntax:** SPF records have strict syntax requirements. Typos, incorrect mechanism usage (e.g., using `TXT` instead of `ip4` or `include`), or misplaced elements can invalidate the record. Always validate your record before publishing.
• **Not Including All Authorized Senders:** Forgetting to list a legitimate third-party service or internal mail server will cause emails sent from those sources to fail SPF checks, impacting deliverability. Maintain a complete inventory.
• **Exceeding the 10 DNS Lookup Limit:** As mentioned in limitations, adding too many `include`, `a`, `mx`, etc., mechanisms will break SPF. Monitor your lookups carefully, especially when adding new vendors.
• **Exceeding Character Limits:** Ensure your record adheres to the 255-character limit per string and overall DNS record size limits.
• **Using the Wrong Record Type:** SPF records must be published as TXT records in DNS. Some older systems used a dedicated SPF record type, but this is deprecated and should not be used.
• **Failing to Update:** If you change email providers, add new services, or decommission old servers, you MUST update your SPF record accordingly. Outdated records can block legitimate mail or leave gaps for abuse.

Make SPF Even Better With PowerDMARC

SPF by itself is effective but has limitations. Cybercriminals have found ways to bypass simple IP address checks, especially by targeting the user-visible ‘From’ address which SPF doesn’t directly protect. SPF technology is made significantly more powerful and relevant when incorporated into DMARC.

We pair SPF with DKIM and DMARC

DMARC requires alignment – meaning the domain used for SPF (in the Return-Path) and/or the domain used for DKIM signing must match the domain in the visible ‘From’ header. PowerDMARC helps you configure DMARC correctly, leveraging both SPF and DKIM results for robust authentication. We take this further with AI-based threat intelligence that helps identify spoofing attacks even when basic checks pass.

Reporting and Feedback

Neither SPF nor DKIM alone gives the domain owner feedback about emails that fail authentication or potential abuse patterns. DMARC enables receiving mail servers to send detailed aggregate (RUA) and forensic (RUF) DMARC reports back to the domain owner. The PowerDMARC platform processes these complex XML reports into easy-to-read charts, tables, and alerts, providing crucial visibility into your email ecosystem, sender compliance, and threats. Using this analytics data, you can refine your SPF/DKIM configurations and adjust your email strategy.

Control What Happens to Unauthenticated Email

DMARC lets you, the domain owner, specify a policy for how receivers should handle emails that fail both SPF and DKIM checks (or fail alignment). You can choose `p=none` (monitor only), `p=quarantine` (send to spam), or `p=reject` (block the email entirely). With PowerDMARC, managing and progressing your DMARC policy towards enforcement becomes much simpler, often achievable with clear guidance and easy interface controls.

• About
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Maitham Al Lawati

Cybersecurity Expert, CEO at PowerDMARC

Maitham is a tech entrepreneur, cybersecurity expert, CEO and Founder of PowerDMARC with 15+ years of industry experience. Maitham holds a Global MBA from the University of Manchester and various professional certifications including CISSP, CISM, CRISC, and ISC2 CCSP.

Latest posts by Maitham Al Lawati (see all)

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