Importance of SPF Flattening in Email Authentication

Sender Policy Framework (SPF) is an email authentication protocol that lets you specify which IP addresses are authorized to send emails from your domain. The receiving email servers check the SPF record of all the incoming messages. An email sent from your domain is only authenticated if its IP address is listed in your SPF record. This helps in improving email authentication and preventing spoofing and phishing attacks. However, SPF also has certain limitations that can make it a little difficult to implement correctly.

There are several common SPF errors people make while creating an SPF record. One of the major and most frequent SPF errors is exceeding the SPF 10-lookup limit. You can make sure that this doesn’t become a problem with SPF flattening. So, before we dive into what SPF flattening is, let’s find out why we need it. 

What is SPF Lookup Failure?

To validate SPF for an email, the receiving mail servers often have to make multiple DNS lookups. However, making too many DNS lookups can make the receiving mail servers vulnerable to denial of service attacks. To prevent this, these servers are not allowed to make more than 10 domain lookups while checking the SPF record for an incoming email. 

As a single email delivery service can use more than one DNS lookup, combining these services can quickly result in the limit being exceeded. For instance, outlook.com uses 8/10 records, gmail.com uses 4/10, Office 365 uses 2/10 and other web hosting providers keep adding additional records, quickly exceeding the imposed limit. 

Exceeding your DNS lookup limit may break the domain validation or authentication, enabling malicious actors to spoof or misuse your domain. This means that once the limit has been exceeded, every email that requires a DNS lookup won’t achieve the complete result. This can also prevent many legitimate emails from delivering successfully without giving you any warning. SPF lookup failure can adversely affect your domain’s reputation as well as deliverability.

How Does SPF Flattening Help?

Now that we have established that exceeding the SPF 10-lookup limit is one of the most serious mistakes you can make while creating an SPF record, let’s talk about what you can do to prevent it. 

SPF flattening offers the most effective solution to the problems caused by the SPF lookup limit. It significantly helps in preventing SPF lookup failure. It reduces the risk of your legitimate emails getting flagged as spam by making it easier for the receiving mail servers to validate SPF.

SPF flattening refers to the replacement of all the domains in your SPF record with their respective IP addresses. It causes SPF compression by eliminating various SPF mechanisms and creating a single SPF record, which contains all IP addresses related to multiple domains. Doing this eliminates the need for DNS lookups. 

Why Opt for TDMARC’s Automatic SPF Flattening?

While SPF flattening can considerably help in avoiding the problems caused by SPF lookup failure, “manual” flattening can be quite complex and has several shortcomings. Email service providers may modify their IP addresses without notifying you, making your SPF record inaccurate. This can lead to various email delivery problems. To rectify this issue, you will have to monitor your service providers constantly and keep an eye out for these changes. 

This is where SPF automatic flattening comes into the picture. TDMARC’s Automatic SPF Flattening feature automatically flattens your SPF record, eliminating any effort on your part. You can simply opt for the Automatic Flattening on the TDMARC dashboard for always returning public DNS queries with a flattened SPF record. It also keeps it updated with modified IPs periodically.

With so much depending on your domain’s reputation and email deliverability, it has become essential to ensure the accuracy of your SPF record. So, make sure your domain’s SPF record is flattened and updated periodically to avoid SPF lookup failure and ensure proper email authentication.