The Sender Policy Framework (SPF) is a security protocol that checks an email sender’s legitimacy. It works like a passport for your emails, verifying the sender’s identity and that the email comes from an authorized source.
An SPF contributes to the security and confidentiality of email communications by confirming that all emails are not from imposters. However, an email can fail SPF validation.
When an SPF fails for IP, the email is not from an authorized source. It’s likened to someone attempting to enter a country with a fake passport.
It also means a red flag email, either a malicious email or a phishing attack.
So, why do emails fail SPF validation? What are its consequences? Read this article to learn more about the SPF, SPF Failures, basic and advanced troubleshooting, and how to avoid them.
What is the SPF or Sender Policy Framework?
An SPF is one of the trio of email security protocols (SPF, DKIM and DMARC) that address a somewhat different aspect of the email puzzle to prevent spam and email phishing.
The three work together via encryption tools and standard authentication to authenticate emails from a domain.
The SPF, in particular, is an email authentication protocol used by recipient mail servers to verify an email’s authenticity by checking if the sender matches their domain name in the “From” field. To do so, SPF lists applications and servers that can send emails from a domain.
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How SPF Works
Let’s assume:
– Your business domain is onlinesportshop.com, and you email your customers and employees from support@onlinesportshop.com;
– Your email delivery server – a software that sends and receives email and a computer system equivalent of your neighborhood mailman – uses an IP address of 192.168.0.1;
– A spammer uses a scam server with an IP address of 1.2.3.4 to send spam or spoofed emails. These emails may contain false information, malicious links, subtle untruths, or outright lies meant to make the sender appear compromised by malware or insecure.
These emails can negatively impact your reputation as the supposed sender and hurt your social prospects and business as a whole.
– Your email delivery server connects to that of your recipients. That email server serving the recipient’s mailbox will extract your domain name (onlinesportshop.com) as the sender.
– The recipient’s email server will also check if the connecting host’s IP address is listed in onlinesportshop.com’s SPF record. That record lists all domains and IP addresses authorized to send emails from that domain.
– The SPF check passes if the IP address is in the list.
– Your SPF record may look like this: v=spf1 ip4:192.168.0.1 -all
– It signifies that only emails from 192.168.0.1 pass the SPF check, and all other IP addresses will fail.
DKIM and SPF complement each other and are interrelated because of their protective features in email security. You might be interested in reading DKIM vs SPF – What’s The Difference?
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What Is an SPF Failure and Why Is This Issue Important?
An “SPF Authentication Fail” error means the sending host is not authorized to use the domain. It’s informally referred to as “hard fail.”
An SPF failure could be caused by inconsistencies in the SPF records’ setup or exceeding the ten lookup limit.
Other reasons that lead to an SPF failure include:
- There are multiple SPF records in your DNS record for the same domain.
- The IP addresses are not listed on the SPF record or have not been updated.
- The receiving Mail Transfer Agent (MTA) cannot find the SPF record published in the DNS.
- The flattened SPF record exceeds the 255 SPF characters limit.
- The SPF void lookup exceeds two (permitted limit).
- The record is syntactically incorrect.
When any of these reasons for SPF failure occur, the SPF authentication results will be passed along to the Domain-based Message Authentication, Reporting & Conformance (DMARC) protocol. DMARC is an email authentication protocol that specifies how to authenticate emails using DKIM or SPF.
After passing through DMARC, the authentication will result in an SPF None, Neutral, Soft Fail, Hard Fail, Temperror (temporary error), or Permerror (permanent error). We will explain each of them in depth below.
Use InboxAlly’s free spam tester to prevent SPF failures. It will show elements of your email that a spam filter could interpret as spam and validate your campaigns before sending them.
Variation of SPF Fail Error: The Difference Between SPF Soft Fail and Hard Fail
An SPF hard fail occurs when a receiving MTA discards or blocks an email from the sending source not listed in your SPF record.
SPF hard fail example
v=spf1 ip4 132.45.55.65 -all
The hyphen sign in front of “all” in this example indicates that any senders not listed in this SPF record are treated as hard fail or unapproved. Thus, emails from those unapproved senders should be deleted.
An SPF soft fail, on the other hand, occurs when the MTA does not accept unauthorized mail. However, emails with IP addresses not included in the SPF record will not be automatically blocked but marked as spam or suspicious.
SPF soft fail example
v=spf1 include:spf.protection.outlook.com ~all
In this valid SPF record, the hyphen in front of “all” indicates that servers not listed in the SPF record are handled as “soft fail.”
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Other Cases When SPF Authentication Fails
SPF None
This qualifier means that the SPF authentication check failed and is also treated as a failure in DMARC. It usually signifies that a domain does not contain an SPF record.
SPF Neutral
The SPF record does not indicate whether the IP address is authorized. Depending on how DMARC is set up on the server, it can be interpreted as pass or fail.
SPF Temporary Error
Also known as the SPF temperror, this qualifier in SPF authentication failure means a transient error, such as a DNS timeout during the check. It causes the email server to temporarily fail.
SPF Permanent Error
Most SPF authentication fails because of the SPF Permerror. It occurs when the receiving MTA renders the SPF record invalid during DNS lookups.
The SPF permanent error typically happens because the lookup limit exceeds ten or the SPF record is syntactically incorrect. Read SPF Limit: It’s Not as Difficult as You Think to learn more.
SPF Record Failures and Its Impact
An SPF failure can affect your email marketing efforts.
It could mean to the recipient servers that your emails are from an unauthorized source and could be malicious or a phishing attack.
Basic Troubleshooting for SPF
Take the following basic troubleshooting to remediate the SPF failure:
- Verify that the SPF is set up correctly and that the outgoing messages pass the SPF authentication check.
- Create a list of email servers authorized to send emails on your behalf, or update your SPF record with a proper email authorization list. Then, use the hard fail flag “-all.”
- Have a defensive SPF record, even for a domain in your organization that does not send emails. Malicious parties may mimic a domain to send malicious or spoofed emails.
- Enable a DMARC policy and set it to reject or quarantine for emails if they’re from unauthorized sources.
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Advanced Troubleshooting for SPF
If the basic troubleshooting steps did not solve the issue, try these steps:
- Check the SPF authentication results in your message headers. You’ll typically find such part of the message as it starts with Authentication-Results text. The note next to it is the entry SPF.
- The message header content may indicate no SPF entry; it includes the best guess record, the result is temp error or perm error, or the SPF result is neutral, softfail, or hardfail.
- You may also check if your SPF text record supports up to 10 lookups.
- Get detailed information about the authentication and email delivery for your domain. You can use Google Workspace reporting tools:
- Authentication report
- Postmaster tools
- Security investigation tools and
- Email log search
How to Avoid SPF Failures
Ensure your SPF record lists all the applications and tools you use to send emails from your domain.
If you receive an SPF failure notification, find out the source of the email and resolve the issue. Moreover, you can use tools to monitor your SPF and other email authentication protocols.
You can also use InboxAlly, a unique deliverability tool, to audit and test the deliverability of your emails. This tool teaches inbox providers, like Yahoo Mail and Gmail, to understand that emails coming from your domains are important and should land in the primary inbox from the start.