SPF misconfigurations are a serious issue that can have far-reaching consequences, from damaging a brand’s reputation to causing financial losses and even legal complications. Despite being a relatively small technical detail, an incorrectly set up SPF record can create big problems.
One of the key best practices is using the -all mechanism in SPF records, yet the reality shows that most domains don’t follow it. According to spf-all.com, out of more than 140 million domains, only a little over 8 million actually use it.
In this guide, we’ll explore what SPF misconfigurations are, why they matter, and how you can avoid them to protect your domain and ensure your emails reach their intended recipients.
Table of Contents
An Introduction to SPF
SPF stands for Sender Policy Framework. It’s an email authentication protocol designed to detect and prevent certain types of fraud carried out through email. Proofpoint defines it as “an email authentication protocol designed to prevent email spoofing, a common technique used in phishing attacks and email spam.”
With SPF, domain owners can specify which email servers are authorized to send messages on behalf of their domain. This is done using a TXT record in the domain’s DNS server. When an email is received, the receiving mail server can check the SPF record of the sending domain to determine whether the message comes from a legitimate source or not.
While SPF alone can’t completely prevent phishing or spam, it’s a crucial part of a domain’s email security. Having a well-configured SPF record is essential if you want your emails to reach their destination. On the other hand, having SPF misconfigurations can cause all kinds of issues.
How SPF Works
Now that we have a basic understanding of SPF, let’s go over exactly how it works, because understanding this is the first step to ensuring you don’t fall victim to SPF misconfigurations.
SPF works by comparing the IP address of the server sending the email with the list of authorized IPs in the domain’s TXT record. When an email reaches a server, the recipient checks the SPF record for the sender’s domain. If the IP of the sending server is in the list of authorized addresses, the email is accepted. If it’s not authorized, the message may be rejected or marked as a “softfail,” depending on the SPF policy for that domain.
An SPF record uses mechanisms like ip4, ip6, include, a, and mx to define authorized senders. A typical SPF record might look like this:
v=spf1 ip4:192.0.2.0/24 include:spf.protection.example -all
In this example, the range of IPs 192.0.2.0/24 is authorized to send emails, as well as the IPs corresponding to the hostname spf.protection.example. The -all at the end means that all other senders should be rejected.
As mentioned earlier, understanding how an SPF record works is a must to avoid misconfigurations.
Common SPF Misconfigurations
Unfortunately, SPF misconfigurations are more common than you might think, and they can severely affect email delivery. They fall under the broader category of security misconfigurations, where small technical mistakes create opportunities for attackers. Some of the most frequent ones include:
- No SPF record at all: Not having an SPF record is a major mistake, as recipients have no way of knowing which servers are authorized to send email for your domain.
- Overly permissive rules: Using mechanisms like +all is one of the major SPF misconfigurations, and can lead to serious spam and phishing problems, since it allows any server to send email on your behalf.
- Syntax errors: If your SPF record’s syntax is incorrect, it won’t work properly and may cause delivery issues.
- Outdated IPs: When switching email providers, some organizations forget to update their SPF record or fail to remove IPs from the old provider. This is a security risk because those old servers would still be authorized to send emails. Similar risks come from MX misconfigurations, where incorrect or outdated mail exchange records can break delivery and weaken security controls.
All SPF misconfigurations come with risks: in some cases, it may cause legitimate emails to never reach their destination; in others, it may inadvertently authorize third parties to send malicious emails in your name. With SPF, even the smallest mistake can have serious consequences.
Consequences
Having incorrect SPF settings can cause all sorts of problems. To begin with, legitimate emails could be blocked or end up in the recipient’s spam folder, disrupting communication with clients and suppliers.
A bad configuration could also mean your domain may be used by spammers, damaging your reputation. Similarly, it could be exploited for phishing attacks, including the creation of phishing subdomains that mimic your brand.
Beyond brand damage, there’s also the issue of increased operational costs. Time and resources would need to be spent investigating and resolving the problems caused. In extreme cases, a company could even face lawsuits, resulting in serious legal complications.
On top of all that, SPF misconfigurations can also negatively impact other protocols like DKIM and DMARC, depending on how their policies are configured.
How to Search for SPF Misconfigurations
The easiest way to look for SPF misconfigurations on your domain is by using our online scanner, which allows you to check multiple aspects of your domain’s security, including any errors in your SPF record.
To scan your domain, start by opening our web misconfiguration scanner. Once there, enter your domain name in the text box and click the “Scan” button.
After a few seconds, you’ll see the results of the analysis, including detailed information on your website’s security and whether there’s anything wrong with your SPF configuration.
If you prefer to use another type of tool, the most recommended is the “dig” command. Thanks to it, it’s easy to check your SPF record. You can run a command like the following from your computer’s terminal tool or command line:
dig TXT yourdomain.com +short
Of course, replace yourdomain.com with your actual domain name. This command will return your domain’s TXT records, including the SPF record. What it won’t do is tell you whether your SPF is properly configured; that’s something you’ll have to check yourself. If you’re unsure, it’s better to use our online scanner as mentioned earlier.
Best Practices for Configuring SPF
An effective SPF record strikes the right balance between security and practicality. As a basic rule, never use the +all mechanism; instead, use -all, which is stricter.
If you change your email service provider, remember to remove from your SPF record any IPs and hostnames that belong to the old provider, ensuring only the ones from your new provider remain.
If you use multiple mechanisms like include, ip4, and mx, make sure they’re set up correctly and that the syntax is right. Review the syntax as many times as necessary before deploying the record in production to avoid SPF misconfigurations.
It’s always a good idea to document any changes you make, along with the date they were made. Keeping a version history of your records is even better.
Don’t forget to combine SPF with other important protocols like DKIM and DMARC, which are now considered essential for ensuring proper email functionality.
SPF and Other Email Authentication Protocols
As mentioned earlier, SPF isn’t the only email authentication protocol. In fact, SPF alone is not enough; you need two more.
One is DKIM (DomainKeys Identified Mail), which adds a cryptographic signature to your emails to verify their integrity. The other is DMARC (Domain-based Message Authentication, Reporting, and Conformance), which sets a policy for how to handle messages that fail authentication checks.
When SPF, DKIM, and DMARC are used together, they provide not only strong authentication but also a powerful defense against spoofing, phishing, and spam. This approach also reduces the risk of phishing subdomains being used to impersonate your organization.
However, if SPF is misconfigured, the ecosystem created by these three records can be disrupted, potentially causing delivery failures depending on your DMARC policies.
Wrapping Up
SPF misconfigurations can block legitimate emails, allow spoofing, and damage your brand’s reputation. They often result from missing records, overly permissive rules, syntax errors, or outdated IPs. Regular checks, proper syntax, and combining SPF with DKIM and DMARC are essential to keeping email secure and ensuring messages are delivered reliably.