What causes SPF authentication to fail? How can SPF Failure be fixed?

spf failure

In this digitally expanding world of emails, the battle against spam and phishing attacks has intensified significantly. To ensure the authenticity of email senders and prevent unauthorized use of domain names, Sender Policy Framework was introduced. 

SPF is an email authentication method that helps detect forged sender addresses and protect recipients from spam and phishing attempts. However, despite its effectiveness, SPF authentication failures can still occur. 
This blog will delve into the common causes behind SPF failures and provide valuable insights on fixing them.

How does SPF authentication work?

SPF authentication is an essential email protocol that ensures the sender’s domain’s legitimacy in an email’s “From” field. The sending MTA determines whether the sending IP is permitted to send emails for that domain by checking a preset list of SPF servers via DNS. However, incorrect SPF record setup can lead to SPF verification failures, impacting email marketing campaigns and customer interactions negatively. To avoid such issues, it is crucial to maintain accurate SPF records and minimize forwarding which further ensures secure and reliable email communications.

Why does SPF Failure Occur? 

SPF authentication failures can occur due to several reasons, including:

Missing SPF Record 

If the receiving Mail Transfer Agent (MTA) fails to find an SPF record published in your domain’s DNS, SPF authentication cannot be completed, leading to failure.

Multiple SPF Records 

Having multiple SPF records published for the same domain can create conflicts, confusing the receiving MTA and resulting in SPF failure.

Outdated SPF Records 

If your Email Service Providers (ESPs) have changed or added IP addresses that are not updated in your SPF record, SPF authentication will fail for those unlisted IPs.

Exceeding DNS Lookup Limit 

If your SPF record requires more than 10 DNS lookups to authenticate, the receiving MTA may stop processing, causing SPF failure.

Void Lookup Limit 

Exceeding the maximum void lookup limit of 2 can also lead to SPF authentication failures.

Exceeding SPF Characters Limit 

If your flattened SPF record length exceeds the allowed 255 characters limit, SPF authentication will fail.

To identify SPF authentication failures and gain valuable insights into your email deliverability, you can monitor your domains using a DMARC analyzer that provides detailed reports on SPF authentication failures. With DMARC reporting enabled, the receiving MTA returns specific SPF authentication failure results for each email, helping you pinpoint and address the issues effectively.

What are the Types of SPF Fail Qualifiers? 

  • “+” Pass: When the SPF record uses the “+all” mechanism, it means that if an email passes SPF authentication (the sender’s IP is authorized), the MTA should accept and deliver it. However, if the email fails SPF authentication, the MTA will not consider this qualifier, and the evaluation will proceed to the next SPF record or mechanism.
  • “-” Fail: The SPF record with the “-all” mechanism indicates that if an email fails SPF authentication, the MTA should reject or mark it as suspicious and not deliver it. This is the strictest approach and is often used when a domain wants to enforce SPF protection strictly.
  • “~” Softfail: With the “~all” mechanism, the SPF record indicates that if an email fails SPF authentication, the MTA should accept it but mark it as potentially suspicious. The email is not outright rejected but treated with caution. Softfail allows the sender to receive feedback about SPF authentication failures without causing immediate delivery issues.
  • “?” Neutral: When the SPF record uses the “?” SPF authentication results won’t impact email delivery because of the “all” technique. The MTA will neither accept nor reject the email based on SPF results. This qualifier is used when a domain does not want to enforce SPF authentication strictly but still wants to receive authentication feedback.

What are the different types of SPF Fail Scenarios?

Case 1: SPF None result is Returned

A “none” result is given if the DNS query performed by the receiving email server fails to locate the domain name in the DNS. The same “none” result is also returned when no SPF record is found in the sender’s DNS, indicating that the sender’s domain lacks SPF authentication configuration. 

Case 2: SPF Neutral Result is Returned

When configuring SPF for your domain, if you include the “?” which refers to a neutral SPF outcome. This means that regardless of the SPF authentication checks for your outbound emails, the receiving Mail Transfer Agent (MTA) returns a neutral result. 

Case 3: SPF Softfail Result

SPF Softfail is denoted by the “~” all mechanism, indicating that the receiving Mail Transfer Agent (MTA) will accept the email and deliver it to the recipient’s inbox. However, if the IP address is not listed in the SPF record found in the DNS, the email will be marked as potentially suspicious or spam. It can be one of the possible reasons for your frequent SPF authentication failures.

Case 4: SPF Hardfail Result

Receiving MTAs will delete emails sent from any sending source that is not listed in your SPF record, which is known as an SPF Hardfail or SPF Fail. To enhance protection against domain impersonation and email spoofing, we highly recommend configuring SPF Hardfail in your SPF record. By doing so, you ensure that only authorized sending sources listed in your SPF record can successfully send emails on behalf of your domain. 

Get more insights into SPF hardfail & softfail here! – SPF hard fail and SPF soft fail

Case 5: SPF TempError (SPF Temporary Error)

SPF TempError, is a frequent and usually innocuous reason behind SPF authentication failures. This error occurs when there is a DNS issue, such as a DNS timeout, while the receiving Mail Transfer Agent (MTA) performs an SPF authentication check. As the name suggests, SPF TempError results in a temporary SPF failure, returning a 4xx status code. However, when the check is retried later, it can yield an SPF pass result. 

Please read our blog on SPF temperror to know more!  What is SPF PermError and How to Fix It?

Summing Up! 

Understanding the common causes of SPF authentication failures and taking proactive steps to fix them is essential for maintaining the integrity of your email communications. By carefully configuring SPF records, minimizing forwarding, and staying vigilant with monitoring and updates, you can significantly reduce SPF failures and ensure that your legitimate emails reach their recipients’ inboxes while protecting them from malicious ones. 

GoDMARC can help secure your emails in no time. Check out our customized pricing plans and sign up for a free 10-day trial. 


Q1. How does SPF authentication failure impact email delivery?

  • SPF failures may result in emails being marked as spam or rejected
  • Failed SPF authentication can harm email deliverability rates
  • Recipients may not receive critical emails due to SPF issues

Q2. How can SPF failure be fixed for better email authentication?

  • Regularly review and update SPF records with accurate information
  • Minimize email forwarding and use DMARC for better control
  • Consolidate multiple SPF records into a single comprehensive one
  • Include all relevant IPs, especially dynamic and large-scale service IPs
  • Monitor SPF authentication results with DMARC to address issues proactively

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