PowerDMARC

SPF Fail: What It Means and How to Fix It

Maitham Al Lawati
SPF fail

Key Takeaways

  1. SPF errors can arise from issues like incorrect syntax, exceeding DNS lookup limits, and multiple SPF records for the same domain.
  2. The SPF mechanism can return different results, including Pass, Fail, Softfail, Neutral, and Temporary Error, each indicating a different level of authentication success.
  3. Combining multiple SPF records into a single one using the “include” mechanism is essential to avoid invalidation of SPF implementation.
  4. Regular monitoring of DMARC reports can help identify the causes of SPF failures and facilitate timely resolutions.
  5. Implementing SPF best practices is critical for safeguarding email deliverability and reducing the likelihood of authentication failures.

Sender Policy Framework (SPF) is an email authentication protocol designed to prevent email spoofing by verifying that messages are sent from authorized mail servers. When properly configured, SPF helps reduce spam and phishing attempts by allowing receiving mail servers to check whether an email comes from a legitimate source. 

However, if something goes wrong in the setup or during the verification process, you may run into an SPF fail. An SPF failure means the recipient’s server could not confirm the sender’s authorization, which often leads to emails being flagged as spam or rejected altogether.

In this post, we’ll look at the most common causes of SPF failures and how to fix them.

What Is SPF in Email Authentication?

Sender Policy Framework (SPF) is an email authentication method that helps verify whether an email is sent from an authorized mail server. Think of it as a list of “approved senders” published in a domain’s DNS records.

The primary role of SPF is to prevent email spoofing, where malicious actors forge the “From” address to trick recipients into believing the email is legitimate. By checking SPF records, receiving mail servers can confirm whether a message truly comes from the domain it claims to represent.

Here’s how SPF works during the email delivery process:

In short, SPF acts as a checkpoint to keep fraudulent emails out of inboxes.

What Does “SPF Fail” Mean?

An SPF fail occurs when the recipient’s mail server determines that the sending server is not authorized to send email on behalf of the domain. This happens if the IP address of the sending server doesn’t match the sources listed in the domain’s SPF record.

Email servers interpret SPF results using mechanisms defined by the SPF policy. The main outcomes include:

When SPF fails, many email providers will either reject the email outright or route it to the spam folder, significantly reducing deliverability.

Stop SPF Failures with PowerDMARC!

Why Do SPF Failures Happen? 

SPF failures can occur due to the following reasons:

When SPF fails for your email, your next steps should be to identify the reason behind it so you can resolve it. This is possible through regular monitoring of DMARC reports. PowerDMARC helps you read reports on SPF authentication failures easily with our DMARC analyzer.

Types of SPF Failures

The following are types of SPF fail qualifiers each of which is added as a prefix before the SPF mechanism:

“+” “Pass”
“-” “Fail”
“~” “Softfail”
“?” “Neutral”

How do these matter? Well in a situation where your email is rejected, you can choose how stringently you want receivers to handle it. You may specify a qualifier to “pass” messages that have received an SPF “Fail” delivery, or take a “Neutral” standpoint (do nothing).

1. SPF None Result Returned

In the first case scenario, if the receiving email server performs a DNS lookup and is unable to find the domain name in the DNS, a none result is returned. None is also returned in case no SPF record is found in the sender’s DNS, which implies that the sender doesn’t have SPF authentication configured for this domain. In this case, SPF authentication for your emails fails, which is denoted by “-all”.

Generate your error-free SPF record now with our free SPF record generator tool to avoid this.

2. SPF Neutral Result Returned

While configuring SPF for your domain, if you have affixed an “?all” mechanism to your SPF record, this means that no matter what the SPF authentication checks for your outbound emails conclude, the receiving MTA returns a neutral result. This happens because when you have your SPF in neutral mode, you are not specifying the IP addresses that are authorized to send emails on your behalf and allowing unauthorized IP addresses to send them as well.

3. SPF Softfail Result Returned

Similar to SPF neutral, SPF softfail is identified by ~all mechanism which implies that the receiving MTA would accept the mail and deliver it into the inbox of the recipient, but it would be marked as spam, in case the IP address is not listed in the SPF record found in the DNS, which can be a reason why SPF authentication fails for your email. Given below is an example of SPF softfail:

 v=spf1 include:spf.google.com ~all

4. SPF Hardfail Result Returned

SPF hardfail is when receiving MTAs discard emails originating from any sending source that is not listed within your SPF record. We recommend you to configure SPF hardfail in your SPF record if you want to gain protection against domain impersonation and email spoofing. 

Example: v=spf1 include:spf.google.com -all

Learn the specific difference of  SPF softfail vs hardfail

5. SPF Temperror (SPF Temporary Error)

One common and often harmless reasons why SPF authentication fails is SPF Temperror (temporary error). This is caused by a DNS error such as a DNS timeout. It is, therefore, just as the name suggests, an interim error returning a 4xx status code that can cause a temporary SPF failure. It will yield an SPF pass result when tried again later.

6. SPF Permerror (SPF Permanent Error)

Another common error that domains face is an SPF Permerror. This is when there is a failure with a permanent error. This happens when your SPF record gets invalidated by the receiving MTA. There are many reasons why SPF might break and be rendered invalid by the MTA while performing DNS lookups:

Note: When an MTA performs an SPF check on an email, it queries the DNS or conducts a DNS lookup to check for the authenticity of the email source. Ideally, in SPF you are allowed a maximum of 10 DNS lookups, exceeding which will cause SPF to break and return a Permerror result. This is a very common issue leading to SPF fail. 

How to Fix An SPF Fail for Emails

For smooth deliverability, it is important to ensure SPF doesn’t fail for your emails. To fix SPF fails, you can follow these best practices: 

1. Stay within SPF Limits

If your authentication fails because of DNS lookups exceeding RFC-specified limits, try to stay within the limit to prevent the failure. PowerDMARC helps customers optimize their SPF records to stay under these hard limits through Macros. Often, they are several times more effective than SPF flattening. However, if you choose to use SPF flattening, SPF flattening tools can simplify the process, though they still require manual updates whenever your email service provider modifies its infrastructure. Macros in your SPF DNS record help you avoid exceeding DNS void and lookup limits at all times.

2. Avoid Syntax and Configuration Errors

Manually implementing SPF records often leads to syntax errors and causes them to fail. To ensure you are using the right syntax for SPF, generate your record with the help of an automated SPF record generator tool.

When configuring SPF in your DNS, always use the resource type “TXT”. If you configure the wrong resource type like “CNAME” or even “SPF”, it will lead to configuration errors and an SPF failure. 

3. Authorize All Sending Sources

Make sure you are properly authorizing all your sending sources including your third-party vendors, in your SPF record. Your vendors often change or add to their list of sending IPs. You must make sure you are on top of such changes and implement them in your own SPF record. Missing out on authorized sending sources often leads to unwarranted SPF failures. 

4. Combine Multiple SPF Records 

More than one SPF record for the same domain can invalidate your SPF implementation and lead to SPF failure. In such cases, it is better to combine multiple records into a single record by using the “include” mechanism. 

Best Practices to Prevent SPF Fail

Domain owners abiding by the above-mentioned SPF best practices can significantly reduce the chances of unwarranted SPF fail. 

In addition, here are some recommended practices businesses should follow to strengthen their overall email security posture:

Email authentication failures are never good news for your domain’s reputation and credibility. Following these practices helps minimize the risk of SPF failures and ensures better email deliverability.

Conclusion

Fixing SPF fails is critical for maintaining trust, protecting your brand reputation, and ensuring reliable email delivery. Without proper SPF configurations, your emails are more likely to be flagged as spam, rejected, or exploited by attackers for spoofing.

The best approach is proactive: regularly monitor your domain, keep SPF records updated, and use multiple email authentication protocols like SPF, DKIM, and DMARC together. This layered defense greatly improves your chances of passing authentication checks and securing your email channel.

Want to make sure your SPF is configured correctly and avoid costly failures? Try out PowerDMARC’s features today to strengthen your email security and protect your domain from abuse.

Frequently Asked Questions

How do I know if my emails are failing SPF?

You can check email headers for SPF results or use tools like DMARC reports and SPF checkers. These will show whether your messages are passing or failing SPF validation.

Can SPF fail cause emails to bounce?

Yes. When SPF fails with a “hard fail” result, receiving servers often reject the message completely, leading to bounces. In other cases, they may accept the message but route it to the spam folder.

Do I need DKIM and DMARC if I have SPF?

Absolutely. SPF alone cannot protect forwarded emails or provide domain-level reporting. DKIM ensures email integrity, and DMARC ties SPF and DKIM together, giving you visibility and stronger protection against spoofing.

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