PowerDMARC

SPF Fail: Common Causes and How to Fix Them

Maitham Al Lawati
SPF fail
Reading Time: 6 min

Have you ever seen your email fail SPF? If you have, I will tell you exactly why SPF authentication fails. Sender Policy Framework, or SPF, is one of the email authentication protocols organizations have used in their email systems for years to reduce spam and authorize sending sources. However, due to unfavorable circumstances, if your SPF fails, this may lead to potential email deliverability issues. 

Here are some common reasons leading to SPF failures: 

SPF Authentication Explained

SPF (Sender Policy Framework) is an email authentication protocol used to verify that the email sender’s IP address is authorized to send emails on behalf of the domain specified in the “From:” field of the message. When an email is sent, the receiving mail server queries the DNS for the SPF record associated with the domain to check if the sending IP address is listed in the record. If the IP address is not authorized, the email may fail SPF verification. 

Understanding the proper setup of SPF records is critical to ensuring that your emails pass authentication checks. This is necessary for successful email marketing efforts or when you’re sending marketing emails to win over customers.

Why Does SPF Fail? 

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 to get reports on SPF authentication failures. 

When you have DMARC reporting enabled, the receiving MTA may return any one of the following SPF failure results for SPF failed emails. Let’s get to know them better:

Types of SPF Failures

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

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

How do these matter? Well in a situation where your email does fail SPF, you can choose how stringently you want receivers to handle it. You may specify a qualifier to “pass” messages that fail SPF check (deliver them), “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.

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 a ?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, also known as SPF fail is when receiving MTAs would 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. Given below is an example of SPF hardfail:

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

5. SPF Temperror (SPF Temporary Error)

One of the very common and often harmless reasons why SPF authentication fails is SPF Temperror (temporary error) which is caused by a DNS error such as a DNS timeout while the receiving MTA is performing an SPF authentication check. It is, therefore, just as the name suggests, usually an interim error returning a 4xx status code that can cause temporary SPF failure, yielding an SPF pass result when tried again later.

6. SPF Permerror (SPF Permanent Error)

Another common result that domain errors are faced with is SPF Permerror. This is when SPF fails 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 SPF Authentication Fail for Emails?

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

1. Stay within SPF Limits

If your SPF fails because of DNS lookups exceeding RFC-specified limits, try to stay within the limit to prevent SPF fail. PowerDMARC helps customers optimize their SPF records to stay under these hard limits through Macros. Several times more effective than SPF flattening, 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 SPF fail. To ensure you are using the right syntax for SPF, generate your record with the help of an automated SPF record generator tool. These free online tools generate instant and error-free DNS records. 

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 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 fail. In such cases, it is better to combine the records into a single record by using the “include” mechanism. 

Following SPF Best Practices to Avoid SPF Failures

Domain owners abiding by the above-mentioned SPF best practices can significantly reduce the chances of unwarranted SPF fail. Here are some additional good practices that businesses can exercise in general to further strengthen their email security: 

Email authentication failures are never good news for your domain’s reputation and credibility. To ensure your deliverability isn’t affected, you need to take action now to prevent your SPF from failing. Want to test if you have SPF configured correctly for your domain? Try out our free SPF checker tool today!

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